TY  - JOUR
A1  - Zöller, Gert
A1  - Hainzl, Sebastian
A1  - Tilmann, Frederik
A1  - Woith, Heiko
A1  - Dahm, Torsten
T1  - Comment on: Wikelski, Martin; Müller, Uschi; Scocco, Paola; Catorci, Andrea; Desinov, Lev V.; Belyaev, Mikhail Y.; Keim, Daniel A.; Pohlmeier, Winfried; Fechteler, Gerhard; Mai, Martin P. : Potential short-term earthquake forecasting by farm animal monitoring. - Ethology. - 126 (2020), 9. - S. 931 - 941. -ISSN 0179-1613. - eISSN 1439-0310. - doi 10.1111/eth.13078
JF  - Ethology
N2  - Based on an analysis of continuous monitoring of farm animal behavior in the region of the 2016 M6.6 Norcia earthquake in Italy, Wikelski et al., 2020; (Seismol Res Lett, 89, 2020, 1238) conclude that animal activity can be anticipated with subsequent seismic activity and that this finding might help to design a "short-term earthquake forecasting method." We show that this result is based on an incomplete analysis and misleading interpretations. Applying state-of-the-art methods of statistics, we demonstrate that the proposed anticipatory patterns cannot be distinguished from random patterns, and consequently, the observed anomalies in animal activity do not have any forecasting power.
KW  - animal behavior
KW  - earthquake precursor
KW  - error diagram
KW  - prediction
KW  - randomness
KW  - statistics
Y1  - 2020
U6  - https://doi.org/10.1111/eth.13105
SN  - 0179-1613
SN  - 1439-0310
VL  - 127
IS  - 3
SP  - 302
EP  - 306
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Ziegler, Moritz O.
A1  - Reiter, Karsten
A1  - Heidbach, Oliver
A1  - Zang, Arno
A1  - Kwiatek, Grzegorz
A1  - Stromeyer, Dietrich
A1  - Dahm, Torsten
A1  - Dresen, Georg
A1  - Hofmann, Gerhard
T1  - Mining-Induced Stress Transfer and Its Relation to a 1.9 Seismic Event in an Ultra-deep South African Gold Mine
JF  - Pure and applied geophysics
N2  - On 27 December 2007, a 1.9 seismic event occurred within a dyke in the deep-level Mponeng Gold Mine, South Africa. From the seismological network of the mine and the one from the Japanese-German Underground Acoustic Emission Research in South Africa (JAGUARS) group, the hypocentral depth (3,509 m), focal mechanism and aftershock location were estimated. Since no mining activity took place in the days before the event, dynamic triggering due to blasting can be ruled out as the cause. To investigate the hypothesis that stress transfer, due to excavation of the gold reef, induced the event, we set up a small-scale high-resolution three-dimensional (3D) geomechanical numerical model. The model consisted of the four different rock units present in the mine: quartzite (footwall), hard lava (hanging wall), conglomerate (gold reef) and diorite (dykes). The numerical solution was computed using a finite-element method with a discretised mesh of approximately elements. The initial stress state of the model is in agreement with in situ data from a neighbouring mine, and the step-wise excavation was simulated by mass removal from the gold reef. The resulting 3D stress tensor and its changes due to mining were analysed based on the Coulomb failure stress changes on the fault plane of the event. The results show that the seismic event was induced regardless of how the Coulomb failure stress changes were calculated and of the uncertainties in the fault plane solution. We also used the model to assess the seismic hazard due to the excavation towards the dyke. The resulting curve of stress changes shows a significant increase in the last in front of the dyke, indicating that small changes in the mining progress towards the dyke have a substantial impact on the stress transfer.
KW  - Induced seismicity
KW  - static stress change
KW  - deep-level mining
KW  - tabular mining
KW  - Coulomb failure stress
KW  - 3D geomechanical numerical model
Y1  - 2015
U6  - https://doi.org/10.1007/s00024-015-1033-x
SN  - 0033-4553
SN  - 1420-9136
VL  - 172
IS  - 10
SP  - 2557
EP  - 2570
PB  - Springer
CY  - Basel
ER  - 
TY  - JOUR
A1  - Zang, Arno
A1  - Stephansson, Ove
A1  - Stenberg, Leif
A1  - Plenkers, Katrin
A1  - von Specht, Sebastian
A1  - Milkereit, Claus
A1  - Schill, Eva
A1  - Kwiatek, Grzegorz
A1  - Dresen, Georg
A1  - Zimmermann, Günter
A1  - Dahm, Torsten
A1  - Weber, Michael
T1  - Hydraulic fracture monitoring in hard rock at 410 m depth with an advanced fluid-injection protocol and extensive sensor array
JF  - Geophysical journal international
N2  - In this paper, an underground experiment at the Aspo Hard Rock Laboratory (HRL) is described. Main goal is optimizing geothermal heat exchange in crystalline rock mass at depth by multistage hydraulic fracturing with minimal impact on the environment, that is, seismic events. For this, three arrays with acoustic emission, microseismicity and electromagnetic sensors are installed mapping hydraulic fracture initiation and growth. Fractures are driven by three different water injection schemes (continuous, progressive and pulse pressurization). After a brief review of hydraulic fracture operations in crystalline rock mass at mine scale, the site geology and the stress conditions at Aspo HRL are described. Then, the continuous, single-flow rate and alternative, multiple-flow rate fracture breakdown tests in a horizontal borehole at depth level 410 m are described together with the monitoring networks and sensitivity. Monitoring results include the primary catalogue of acoustic emission hypocentres obtained from four hydraulic fractures with the in situ trigger and localizing network. The continuous versus alternative water injection schemes are discussed in terms of the fracture breakdown pressure, the fracture pattern from impression packer result and the monitoring at the arrays. An example of multistage hydraulic fracturing with several phases of opening and closing of fracture walls is evaluated using data from acoustic emissions, seismic broad-band recordings and electromagnetic signal response. Based on our limited amount of in situ tests (six) and evaluation of three tests in Avro granodiorite, in the multiple-flow rate test with progressively increasing target pressure, the acoustic emission activity starts at a later stage in the fracturing process compared to the conventional fracturing case with continuous water injection. In tendency, also the total number and magnitude of acoustic events are found to be smaller in the progressive treatment with frequent phases of depressurization.
KW  - Geomechanics
KW  - Fracture and flow
KW  - Broad-band seismometers
Y1  - 2016
SN  - 0956-540X
SN  - 1365-246X
VL  - 208
SP  - 790
EP  - 813
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Woith, Heiko
A1  - Petersen, Gesa Maria
A1  - Hainzl, Sebastian
A1  - Dahm, Torsten
T1  - Review: Can Animals Predict Earthquakes?
JF  - Bulletin of the Seismological Society of America
N2  - In public perception, abnormal animal behavior is widely assumed to be a potential earthquake precursor, in strong contrast to the viewpoint in natural sciences. Proponents of earthquake prediction via animals claim that animals feel and react abnormally to small changes in environmental and physico-chemical parameters related to the earthquake preparation process. In seismology, however, observational evidence for changes of physical parameters before earthquakes is very weak. In this study, we reviewed 180 publications regarding abnormal animal behavior before earthquakes and analyze and discuss them with respect to (1) magnitude-distance relations, (2) foreshock activity, and (3) the quality and length of the published observations. More than 700 records of claimed animal precursors related to 160 earthquakes are reviewed with unusual behavior of more than 130 species. The precursor time ranges from months to seconds prior to the earthquakes, and the distances from a few to hundreds of kilometers. However, only 14 time series were published, whereas all other records are single observations. The time series are often short (the longest is 1 yr), or only small excerpts of the full data set are shown. The probability density of foreshocks and the occurrence of animal precursors are strikingly similar, suggesting that at least parts of the reported animal precursors are in fact related to foreshocks. Another major difficulty for a systematic and statistical analysis is the high diversity of data, which are often only anecdotal and retrospective. The study clearly demonstrates strong weaknesses or even deficits in many of the published reports on possible abnormal animal behavior. To improve the research on precursors, we suggest a scheme of yes and no questions to be assessed to ensure the quality of such claims.
Y1  - 2018
U6  - https://doi.org/10.1785/0120170313
SN  - 0037-1106
SN  - 1943-3573
VL  - 108
IS  - 3A
SP  - 1031
EP  - 1045
PB  - Seismological Society of America
CY  - Albany
ER  - 
TY  - JOUR
A1  - Valenzuela-Malebran, Carla
A1  - Cesca, Simone
A1  - Lopez-Comino, José Ángel
A1  - Zeckra, Martin
A1  - Krüger, F.
A1  - Dahm, Torsten
T1  - Source mechanisms and rupture processes of the Jujuy seismic nest, Chile-Argentina border
JF  - Journal of South American earth sciences
N2  - The Altiplano-Puna plateau, in Central Andes, is the second-largest continental plateau on Earth, extending between 22 degrees and 27 degrees S at an average altitude of 4400 m. The Puna plateau has been formed in consequence of the subduction of the oceanic Nazca Plate beneath the continental South American plate, which has an average crustal thickness of 50 km at this location. A large seismicity cluster, the Jujuy cluster, is observed at depth of 150-250 km beneath the central region of the Puna plateau. The cluster is seismically very active, with hundreds of earthquakes reported and a peak magnitude MW 6.6 on 25th August 2006. The cluster is situated in one of three band of intermediate-depth focus seismicity, which extend parallel to the trench roughly North to South. It has been hypothesized that the Jujuy cluster could be a seismic nest, a compact seismogenic region characterized by a high stationary activity relative to its surroundings. In this study, we collected more than 40 years of data from different catalogs and proof that the cluster meets the three conditions of a seismic nest. Compared to other known intermediate depth nests at Hindu Kush (Afganisthan) or Bucaramanga (Colombia), the Jujuy nest presents an outstanding seismicity rate, with more than 100 M4+ earthquakes per year. We additionally performed a detailed analysis of the rupture process of some of the largest earthquakes in the nest, by means of moment tensor inversion and directivity analysis. We focused on the time period 2017-2018, where the seismic monitoring was the most extended. Our results show that earthquakes in the nest take place within the eastward subducting oceanic plate, but rupture along sub-horizontal planes dipping westward. We suggest that seismicity at Jujuy nest is controlled by dehydration processes, which are also responsible for the generation of fluids ascending to the crust beneath the Puna volcanic region. We use the rupture plane and nest geometry to provide a constraint to maximal expected magnitude, which we estimate as MW -6.7.
KW  - Seismic nest
KW  - Intermediate-deep earthquakes
KW  - Cluster analysis moment
KW  - tensor inversion
KW  - directivity analysis
Y1  - 2022
U6  - https://doi.org/10.1016/j.jsames.2022.103887
SN  - 0895-9811
SN  - 1873-0647
VL  - 117
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Tilmann, F.
A1  - Zhang, Y.
A1  - Moreno, M.
A1  - Saul, J.
A1  - Eckelmann, F.
A1  - Palo, M.
A1  - Deng, Z.
A1  - Babeyko, Andrey
A1  - Chen, K.
A1  - Báez, Juan Carlos
A1  - Schurr, B.
A1  - Wang, R.
A1  - Dahm, Torsten
T1  - The 2015 Illapel earthquake, central Chile: A type case for a characteristic earthquake?
JF  - Geophysical research letters
N2  - On 16 September 2015, the M-W = 8.2 Illapel megathrust earthquake ruptured the Central Chilean margin. Combining inversions of displacement measurements and seismic waveforms with high frequency (HF) teleseismic backprojection, we derive a comprehensive description of the rupture, which also predicts deep ocean tsunami wave heights. We further determine moment tensors and obtain accurate depth estimates for the aftershock sequence. The earthquake nucleated near the coast but then propagated to the north and updip, attaining a peak slip of 5-6 m. In contrast, HF seismic radiation is mostly emitted downdip of the region of intense slip and arrests earlier than the long period rupture, indicating smooth slip along the shallow plate interface in the final phase. A superficially similar earthquake in 1943 with a similar aftershock zone had a much shorter source time function, which matches the duration of HF seismic radiation in the recent event, indicating that the 1943 event lacked the shallow slip.
Y1  - 2016
U6  - https://doi.org/10.1002/2015GL066963
SN  - 0094-8276
SN  - 1944-8007
VL  - 43
SP  - 574
EP  - 583
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Sen, Ali Tolga
A1  - Cesca, Simone
A1  - Bischoff, Monika
A1  - Meier, Thomas
A1  - Dahm, Torsten
T1  - Automated full moment tensor inversion of coal mining-induced seismicity
JF  - Geophysical journal international
N2  - Seismicity induced by coal mining in the Ruhr region, Germany, has been monitored continuously over the last 25 yr. In 2006, a dense temporary network (HAMNET) was deployed to locally monitor seismicity induced by longwall mining close to the town of Hamm. Between 2006 July and 2007 July, more than 7000 events with magnitudes M-L from -1.7 to 2.0 were detected. The spatiotemporal distribution of seismicity shows high correlation with the mining activity. In order to monitor rupture processes, we set up an automated source inversion routine and successfully perform double couple and full moment tensor (MT) inversions for more than 1000 events with magnitudes above M-L -0.5. The source inversion is based on a full waveform approach, both in the frequency and in the time domain, providing information about the centroid location, focal mechanism, scalar moment and full MT. Inversion results indicate a strong dominance of normal faulting focal mechanisms, with a steeper plane and a subhorizontal one. Fault planes are oriented parallel to the mining stopes. We classify the focal mechanisms based on their orientation and observe different frequency-magnitude distributions for families of events with different focal mechanisms; the overall frequency-magnitude distribution is not fitting the Gutenberg-Richter relation. Full MTs indicate that non-negligible opening tensile components accompanied normal faulting source mechanisms. Finally, extended source models are investigated for largest events. Results suggest that the rupture processes mostly occurred along the subvertical planes.
KW  - Geomechanics
KW  - Fracture and flow
KW  - Earthquake source observations
KW  - Seismicity and tectonics
Y1  - 2013
U6  - https://doi.org/10.1093/gji/ggt300
SN  - 0956-540X
SN  - 1365-246X
VL  - 195
IS  - 2
SP  - 1267
EP  - 1281
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Richter, Gudrun
A1  - Hainzl, Sebastian
A1  - Dahm, Torsten
A1  - Zöller, Gert
T1  - Stress-based, statistical modeling of the induced seismicity at the Groningen gas field
BT  - the Netherlands
JF  - Environmental earth sciences
N2  - Groningen is the largest onshore gas field under production in Europe. The pressure depletion of the gas field started in 1963. In 1991, the first induced micro-earthquakes have been located at reservoir level with increasing rates in the following decades. Most of these events are of magnitude less than 2.0 and cannot be felt. However, maximum observed magnitudes continuously increased over the years until the largest, significant event with ML=3.6 was recorded in 2014, which finally led to the decision to reduce the production. This causal sequence displays the crucial role of understanding and modeling the relation between production and induced seismicity for economic planing and hazard assessment. Here we test whether the induced seismicity related to gas exploration can be modeled by the statistical response of fault networks with rate-and-state-dependent frictional behavior. We use the long and complete local seismic catalog and additionally detailed information on production-induced changes at the reservoir level to test different seismicity models. Both the changes of the fluid pressure and of the reservoir compaction are tested as input to approximate the Coulomb stress changes. We find that the rate-and-state model with a constant tectonic background seismicity rate can reproduce the observed long delay of the seismicity onset. In contrast, so-called Coulomb failure models with instantaneous earthquake nucleation need to assume that all faults are initially far from a critical state of stress to explain the delay. Our rate-and-state model based on the fluid pore pressure fits the spatiotemporal pattern of the seismicity best, where the fit further improves by taking the fault density and orientation into account. Despite its simplicity with only three free parameters, the rate-and-state model can reproduce the main statistical features of the observed activity.
KW  - induced seismicity
KW  - modeling
KW  - statistical seismology
KW  - forecast
Y1  - 2020
U6  - https://doi.org/10.1007/s12665-020-08941-4
SN  - 1866-6280
SN  - 1866-6299
VL  - 79
IS  - 11
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Polom, Ulrich
A1  - Alrshdan, Hussam
A1  - Al-Halbouni, Djamil
A1  - Holohan, Eoghan P.
A1  - Dahm, Torsten
A1  - Sawarieh, Ali
A1  - Atallah, Mohamad Y.
A1  - Krawczyk, Charlotte M.
T1  - Shear wave reflection seismic yields subsurface dissolution and subrosion patterns
BT  - application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan
JF  - Solid earth
N2  - Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development. For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area. The most surprising result of the survey is the absence of evidence of a thick (>2-10 m) compacted salt layer formerly suggested to lie at ca. 35-40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.
Y1  - 2018
U6  - https://doi.org/10.5194/se-9-1079-2018
SN  - 1869-9510
SN  - 1869-9529
VL  - 9
IS  - 5
SP  - 1079
EP  - 1098
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - GEN
A1  - Polom, Ulrich
A1  - Alrshdan, Hussam
A1  - Al-Halbouni, Djamil
A1  - Holohan, Eoghan P.
A1  - Dahm, Torsten
A1  - Sawarieh, Ali
A1  - Atallah, Mohamad Y.
A1  - Krawczyk, Charlotte M.
T1  - Shear wave reflection seismic yields subsurface dissolution and subrosion patterns
BT  - application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan
T2  - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe
N2  - Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development.

For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area.

The most surprising result of the survey is the absence of evidence of a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 979 
KW  - salt dissolution
KW  - hazard
KW  - coast
KW  - area
KW  - subsidence
KW  - shoreline
KW  - karst
KW  - lake
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459134
SN  - 1866-8372
IS  - 979
SP  - 1079
EP  - 1098
ER  - 
TY  - JOUR
A1  - Pirli, Myrto
A1  - Hainzl, Sebastian
A1  - Schweitzer, Johannes
A1  - Köhler, Andreas
A1  - Dahm, Torsten
T1  - Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity
JF  - Earth & planetary science letters
N2  - We observe remarkably periodic patterns of seismicity rates and magnitudes at the Fimbul Ice Shelf, East Antarctica, correlating with the cycles of the ocean tide. Our analysis covers 19 years of continuous seismic recordings from Antarctic broadband stations. Seismicity commences abruptly during austral summer 2011 at a location near the ocean front in a shallow water region. Dozens of highly repetitive events occur in semi-diurnal cycles, with magnitudes and rates fluctuating steadily with the tide. In contrast to the common unpredictability of earthquake magnitudes, the event magnitudes show deterministic trends within single cycles and strong correlations with spring tides and tide height. The events occur quasi-periodically and the highly constrained event sources migrate landwards during rising tide. We show that a simple, mechanical model can explain most of the observations. Our model assumes stick-slip motion on a patch of grounded ice shelf, which is forced by the variations of the ocean-tide height and ice flow. The well fitted observations give new insights into the general process of frictional triggering of earthquakes, while providing independent evidence of variations in ice shelf thickness and grounding.
KW  - tidally modulated cryogenic seismicity
KW  - stick-slip motion
KW  - event recurrence predictability
KW  - ice-shelf thickness
KW  - ice-shelf grounding
KW  - East Antarctica
Y1  - 2018
U6  - https://doi.org/10.1016/j.epsl.2018.09.024
SN  - 0012-821X
SN  - 1385-013X
VL  - 503
SP  - 78
EP  - 87
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Passarelli, Luigi
A1  - Hainzl, Sebastian
A1  - Cesca, Simone
A1  - Maccaferri, Francesco
A1  - Mucciarelli, Marco
A1  - Rößler, Dirk
A1  - Corbi, Fabio
A1  - Dahm, Torsten
A1  - Rivalta, Eleonora
T1  - Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy
JF  - Geophysical journal international
N2  - Tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency-magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg-Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M-w = 4.2 and M-w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M-l > 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been 'passive' features, with small fault patches failing on largely locked faults, or may have been accompanied by an 'active', largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area.
KW  - Seismicity and tectonics
KW  - Statistical seismology
KW  - Dynamics: seismotectonics
Y1  - 2015
U6  - https://doi.org/10.1093/gji/ggv111
SN  - 0956-540X
SN  - 1365-246X
VL  - 201
IS  - 3
SP  - 1553
EP  - 1567
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - GEN
A1  - Passarelli, Luigi
A1  - Hainzl, Sebastian
A1  - Cesca, Simone
A1  - Maccaferri, Francesco
A1  - Mucciarelli, Marco
A1  - Roessler, Dirk
A1  - Corbi, Fabio
A1  - Dahm, Torsten
A1  - Rivalta, Eleonora
T1  - Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy (vol 201, pg 1553, 2015)
T2  - Geophysical journal international
KW  - Seismicity and tectonics
KW  - Statistical seismology
KW  - Dynamics: seismotectonics
Y1  - 2016
U6  - https://doi.org/10.1093/gji/ggv425
SN  - 0956-540X
SN  - 1365-246X
VL  - 204
SP  - 365
EP  - 365
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Nooshiri, Nima
A1  - Saul, Joachim
A1  - Heimann, Sebastian
A1  - Tilmann, Frederik
A1  - Dahm, Torsten
T1  - Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms
JF  - Geophysical journal international
N2  - Global earthquake locations are often associated with very large systematic travel-time residuals even for clear arrivals, especially for regional and near-regional stations in subduction zones because of their strongly heterogeneous velocity structure. Travel-time corrections can drastically reduce travel-time residuals at regional stations and, in consequence, improve the relative location accuracy. We have extended the shrinking-box source-specific station terms technique to regional and teleseismic distances and adopted the algorithm for probabilistic, nonlinear, global-search location. We evaluated the potential of the method to compute precise relative hypocentre locations on a global scale. The method has been applied to two specific test regions using existing P- and pP-phase picks. The first data set consists of 3103 events along the Chilean margin and the second one comprises 1680 earthquakes in the Tonga-Fiji subduction zone. Pick data were obtained from the GEOFON earthquake bulletin, produced using data from all available, global station networks. A set of timing corrections varying as a function of source position was calculated for each seismic station. In this way, we could correct the systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure without explicitly solving for a velocity model. Residual statistics show that the median absolute deviation of the travel-time residuals is reduced by 40-60 per cent at regional distances, where the velocity anomalies are strong. Moreover, the spread of the travel-time residuals decreased by similar to 20 per cent at teleseismic distances (>28 degrees). Furthermore, strong variations in initial residuals as a function of recording distance are smoothed out in the final residuals. The relocated catalogues exhibit less scattered locations in depth and sharper images of the seismicity associated with the subducting slabs. Comparison with a high-resolution local catalogue reveals that our relocation process significantly improves the hypocentre locations compared to standard locations.
KW  - Seismicity and tectonics
KW  - Computational seismology
KW  - Subduction zone processes
KW  - Pacific Ocean
KW  - South America
Y1  - 2016
U6  - https://doi.org/10.1093/gji/ggw405
SN  - 0956-540X
SN  - 1365-246X
VL  - 208
IS  - 2
SP  - 589
EP  - 602
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Nooshiri, Nima
A1  - Bean, Christopher J.
A1  - Dahm, Torsten
A1  - Grigoli, Francesco
A1  - Kristjansdottir, Sigriour
A1  - Obermann, Anne
A1  - Wiemer, Stefan
T1  - A multibranch, multitarget neural network for rapid point-source inversion in a microseismic environment
BT  - examples from the Hengill Geothermal Field, Iceland
JF  - Geophysical journal international
N2  - Despite advanced seismological techniques, automatic source characterization for microseismic earthquakes remains difficult and challenging since current inversion and modelling of high-frequency signals are complex and time consuming. For real-time applications such as induced seismicity monitoring, the application of standard methods is often not fast enough for true complete real-time information on seismic sources. In this paper, we present an alternative approach based on recent advances in deep learning for rapid source-parameter estimation of microseismic earthquakes. The seismic inversion is represented in compact form by two convolutional neural networks, with individual feature extraction, and a fully connected neural network, for feature aggregation, to simultaneously obtain full moment tensor and spatial location of microseismic sources. Specifically, a multibranch neural network algorithm is trained to encapsulate the information about the relationship between seismic waveforms and underlying point-source mechanisms and locations. The learning-based model allows rapid inversion (within a fraction of second) once input data are available. A key advantage of the algorithm is that it can be trained using synthetic seismic data only, so it is directly applicable to scenarios where there are insufficient real data for training. Moreover, we find that the method is robust with respect to perturbations such as observational noise and data incompleteness (missing stations). We apply the new approach on synthesized and example recorded small magnitude (M <= 1.6) earthquakes at the Hellisheioi geothermal field in the Hengill area, Iceland. For the examined events, the model achieves excellent performance and shows very good agreement with the inverted solutions determined through standard methodology. In this study, we seek to demonstrate that this approach is viable for microseismicity real-time estimation of source parameters and can be integrated into advanced decision-support tools for controlling induced seismicity.
KW  - Neural networks
KW  - fuzzy logic
KW  - Computational seismology
KW  - Induced seismicity
KW  - Earthquake source observations
Y1  - 2021
U6  - https://doi.org/10.1093/gji/ggab511
SN  - 0956-540X
SN  - 1365-246X
VL  - 229
IS  - 2
SP  - 999
EP  - 1016
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Niemz, Peter
A1  - Dahm, Torsten
A1  - Milkereit, Claus
A1  - Cesca, Simone
A1  - Petersen, Gesa Maria
A1  - Zang, Arno
T1  - Insights into hydraulic fracture growth gained from a joint analysis of seismometer-derived tilt signals and scoustic emissions
JF  - Journal of geophysical research : Solid earth
N2  - Hydraulic fracturing is performed to enhance rock permeability, for example, in the frame of geothermal energy production or shale gas exploitation, and can potentially trigger induced seismicity. The tracking of increased permeabilities and the fracturing extent is often based on the microseismic event distribution within the stimulated rock volume, but it is debated whether the microseismic activity adequately depicts the fracture formation. We are able to record tilt signals that appear as long-period transients (<180 s) on two broadband seismometers installed close (17-72 m) to newly formed, meter-scale hydraulic fractures. With this observation, we can overcome the limitations of the microseismic monitoring alone and verify the fracture mapping. Our analysis for the first time combines a catalog of previously analyzed acoustic emissions ([AEs] durations of 20 ms), indirectly mapping the fractures, with unique tilt signals, that provide independent, direct insights into the deformation of the rock. The analysis allows to identify different phases of the fracturing process including the (re)opening, growth, and aftergrowth of fractures. Further, it helps to differentiate between the formation of complex fracture networks and single macrofractures, and it validates the AE fracture mapping. Our findings contribute to a better understanding of the fracturing processes, which may help to reduce fluid-injection-induced seismicity and validate efficient fracture formation. <br /> Plain Language Summary Hydraulic fracturing (HF) describes the opening of fractures in rocks by injecting fluids under high pressure. The new fractures not only can facilitate the extraction of shale gas but can also be used to heat up water in the subsurface in enhanced geothermal systems, a corner stone of renewable energy production. The fracture formation is inherently accompanied by small, nonfelt earthquakes (microseismic events). Occasionally, larger events felt by the population can be induced by the subsurface operations. Avoiding such events is important for the acceptance of HF operations and requires a detailed knowledge about the fracture formation. We jointly analyze two very different data sets recorded during mine-scale HF experiments: (a) the tilting of the ground caused by the opening of the fractures, as recorded by broadband seismometers-usually deployed for earthquake monitoring-installed close to the experiments and (b) a catalog of acoustic emissions, seismic signals of few milliseconds emitted by tiny cracks around the forming hydraulic fracture. The novel joint analysis allows to characterize the fracturing processes in greater detail, contributing to the understanding of the physical processes, which may help to understand fluid-injection-induced seismicity and validate the formation of hydraulic fractures.
KW  - hydraulic fracturing
KW  - fracture growth
KW  - tilt
KW  - acoustic emissions
KW  - injections
KW  - broadband seismometer
Y1  - 2021
U6  - https://doi.org/10.1029/2021JB023057
SN  - 2169-9313
SN  - 2169-9356
VL  - 126
IS  - 12
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Niemz, Peter
A1  - Cesca, Simone
A1  - Heimann, Sebastian
A1  - Grigoli, Francesco
A1  - von Specht, Sebastian
A1  - Hammer, Conny
A1  - Zang, Arno
A1  - Dahm, Torsten
T1  - Full-waveform-based characterization of acoustic emission activity in a mine-scale experiment
BT  - a comparison of conventional and advanced hydraulic fracturing schemes
JF  - Geophysical journal international / the Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society
N2  - Understanding fracturing processes and the hydromechanical relation to induced seismicity is a key question for enhanced geothermal systems (EGS). Commonly massive fluid injection, predominately causing hydroshearing, are used in large-scale EGS but also hydraulic fracturing approaches were discussed. To evaluate the applicability of hydraulic fracturing techniques in EGS, six in situ, multistage hydraulic fracturing experiments with three different injection schemes were performed under controlled conditions in crystalline rock at the Aspo Hard Rock Laboratory (Sweden). During the experiments the near-field ground motion was continuously recorded by 11 piezoelectric borehole sensors with a sampling rate of 1 MHz. The sensor network covered a volume of 30x30x30 m around a horizontal, 28-m-long injection borehole at a depth of 410 m. To extract and characterize massive, induced, high-frequency acoustic emission (AE) activity from continuous recordings, a semi-automated workflow was developed relying on full waveform based detection, classification and location procedures. The approach extended the AE catalogue from 196 triggered events in previous studies to more than 19600 located AEs. The enhanced catalogue, for the first time, allows a detailed analysis of induced seismicity during single hydraulic fracturing experiments, including the individual fracturing stages and the comparison between injection schemes. Beside the detailed study of the spatio-temporal patterns, event clusters and the growth of seismic clouds, we estimate relative magnitudes and b-values of AEs for conventional, cyclic progressive and dynamic pulse injection schemes, the latter two being fatigue hydraulic fracturing techniques. While the conventional fracturing leads to AE patterns clustered in planar regions, indicating the generation of a single main fracture plane, the cyclic progressive injection scheme results in a more diffuse, cloud-like AE distribution, indicating the activation of a more complex fracture network. For a given amount of hydraulic energy (pressure multiplied by injected volume) pumped into the system, the cyclic progressive scheme is characterized by a lower rate of seismicity, lower maximum magnitudes and significantly larger b-values, implying an increased number of small events relative to the large ones. To our knowledge, this is the first direct comparison of high resolution seismicity in a mine-scale experiment induced by different hydraulic fracturing schemes.
KW  - Fracture and flow
KW  - Spatial analysis
KW  - Statistical methods
KW  - Time-series analysis
KW  - Induced seismicity
Y1  - 2020
U6  - https://doi.org/10.1093/gji/ggaa127
SN  - 0955-419X
SN  - 1365-246X
VL  - 222
IS  - 1
SP  - 189
EP  - 206
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Maghsoudi, Samira
A1  - Hainzl, Sebastian
A1  - Cesca, Simone
A1  - Dahm, Torsten
A1  - Kaiser, Diethelm
T1  - Identification and characterization of growing large-scale en-echelon fractures in a salt mine
JF  - Geophysical journal international
N2  - The spatiotemporal seismicity of acoustic emission (AE) events recorded in the Morsleben salt mine is investigated. Almost a year after backfilling of the cavities from 2003, microevents are distributed with distinctive stripe shapes above cavities at different depth levels. The physical forces driving the creation of these stripes are still unknown. This study aims to find the active stripes and track fracture developments over time by combining two different temporal and spatial clustering techniques into a single methodological approach. Anomalous seismicity parameters values like sharp b-value changes for two active stripes are good indicators to explain possible stress accumulation at the stripe tips. We identify the formation of two new seismicity stripes and show that the AE activities in active clusters are migrated mostly unidirectional to eastward and upward. This indicates that the growth of underlying macrofractures is controlled by the gradient of extensional stress. Studying size distribution characteristic in terms of frequency-magnitude distribution and b-value in active phase and phase with constant seismicity rate show that deviations from the Gutenberg-Richter power law can be explained by the inclusion of different activity phases: (1) the inactive period before the formation of macrofractures, which is characterized by a deficit of larger events (higher b-values) and (2) the period of fracture growth characterized by the occurrence of larger events (smaller b-values).
KW  - Earthquake source observations
KW  - Statistical seismology
Y1  - 2014
U6  - https://doi.org/10.1093/gji/ggt443
SN  - 0956-540X
SN  - 1365-246X
VL  - 196
IS  - 2
SP  - 1092
EP  - 1105
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Maghsoudi, Samira
A1  - Cesca, Simone
A1  - Hainzl, Sebastian
A1  - Kaiser, Diethelm
A1  - Becker, Dirk
A1  - Dahm, Torsten
T1  - Improving the estimation of detection probability and magnitude of completeness in strongly heterogeneous media, an application to acoustic emission (AE)
JF  - Geophysical journal international
N2  - Reliable estimations of magnitude of completeness (M-c) are essential for a correct interpretation of seismic catalogues. The spatial distribution of M-c may be strongly variable and difficult to assess in mining environments, owing to the presence of galleries, cavities, fractured regions, porous media and different mineralogical bodies, as well as in consequence of inhomogeneous spatial distribution of the seismicity. We apply a 3-D modification of the probabilistic magnitude of completeness (PMC) method, which relies on the analysis of network detection capabilities. In our approach, the probability to detect an event depends on its magnitude, source receiver Euclidian distance and source receiver direction. The suggested method is proposed for study of the spatial distribution of the magnitude of completeness in a mining environment and here is applied to a 2-months acoustic emission (AE) data set recorded at the Morsleben salt mine, Germany. The dense seismic network and the large data set, which includes more than one million events, enable a detailed testing of the method. This method is proposed specifically for strongly heterogeneous media. Besides, it can also be used for specific network installations, with sensors with a sensitivity, dependent on the direction of the incoming wave (e.g. some piezoelectric sensors). In absence of strong heterogeneities, the standards PMC approach should be used. We show that the PMC estimations in mines strongly depend on the source receiver direction, and cannot be correctly accounted using a standard PMC approach. However, results can be improved, when adopting the proposed 3-D modification of the PMC method. Our analysis of one central horizontal and vertical section yields a magnitude of completeness of about M-c approximate to 1 (AE magnitude) at the centre of the network, which increases up to M-c approximate to 4 at further distances outside the network; the best detection performance is estimated for a NNE-SSE elongated region, which corresponds to the strike direction of the low-attenuating salt body. Our approach provides us with small-scale details about the capability of sensors to detect an earthquake, which can be linked to the presence of heterogeneities in specific directions. Reduced detection performance in presence of strong structural heterogeneities (cavities) is confirmed by synthetic waveform modelling in heterogeneous media.
KW  - Seismic attenuation
KW  - Statistical seismology
Y1  - 2013
U6  - https://doi.org/10.1093/gji/ggt049
SN  - 0956-540X
VL  - 193
IS  - 3
SP  - 1556
EP  - 1569
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Maghsoudi, Samira
A1  - Cesca, Simone
A1  - Hainzl, Sebastian
A1  - Dahm, Torsten
A1  - Zöller, Gert
A1  - Kaiser, Diethelm
T1  - Maximum Magnitude of Completeness in a Salt Mine
JF  - Bulletin of the Seismological Society of America
N2  - In this study, we analyze acoustic emission (AE) data recorded at the Morsleben salt mine, Germany, to assess the catalog completeness, which plays an important role in any seismicity analysis. We introduce the new concept of a magnitude completeness interval consisting of a maximum magnitude of completeness (M-c(max)) in addition to the well-known minimum magnitude of completeness. This is required to describe the completeness of the catalog, both for the smallest events (for which the detection performance may be low) and for the largest ones (which may be missed because of sensors saturation). We suggest a method to compute the maximum magnitude of completeness and calculate it for a spatial grid based on (1) the prior estimation of saturation magnitude at each sensor, (2) the correction of the detection probability function at each sensor, including a drop in the detection performance when it saturates, and (3) the combination of detection probabilities of all sensors to obtain the network detection performance. The method is tested using about 130,000 AE events recorded in a period of five weeks, with sources confined within a small depth interval, and an example of the spatial distribution of M-c(max) is derived. The comparison between the spatial distribution of M-c(max) and of the maximum possible magnitude (M-max), which is here derived using a recently introduced Bayesian approach, indicates that M-max exceeds M-c(max) in some parts of the mine. This suggests that some large and important events may be missed in the catalog, which could lead to a bias in the hazard evaluation.
Y1  - 2015
U6  - https://doi.org/10.1785/0120140039
SN  - 0037-1106
SN  - 1943-3573
VL  - 105
IS  - 3
SP  - 1491
EP  - 1501
PB  - Seismological Society of America
CY  - Albany
ER  - 
TY  - JOUR
A1  - Kühn, Daniela
A1  - Hainzl, Sebastian
A1  - Dahm, Torsten
A1  - Richter, Gudrun
A1  - Vera Rodriguez, Ismael
T1  - A review of source models to further the understanding of the seismicity of the Groningen field
JF  - Netherlands journal of geosciences : NJG
N2  - The occurrence of felt earthquakes due to gas production in Groningen has initiated numerous studies and model attempts to understand and quantify induced seismicity in this region. The whole bandwidth of available models spans the range from fully deterministic models to purely empirical and stochastic models. In this article, we summarise the most important model approaches, describing their main achievements and limitations. In addition, we discuss remaining open questions and potential future directions of development.
KW  - deterministic
KW  - empirical
KW  - hybrid
KW  - machine learning
KW  - seismicity model
Y1  - 2022
U6  - https://doi.org/10.1017/njg.2022.7
SN  - 0016-7746
SN  - 1573-9708
VL  - 101
PB  - Cambridge Univ. Press
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kuhn, Daniela
A1  - Ohrnberger, Matthias
A1  - Dahm, Torsten
T1  - Imaging a shallow salt diapir using ambient seismic vibrations beneath the densely built-up city area of Hamburg, Northern Germany
JF  - Journal of seismology
N2  - Salt diapirs are common features of sedimentary basins. If close to the surface, they can bear a significant hazard due to possible dissolution sinkholes, karst formation and collapse dolines or their influence on ground water chemistry. We investigate the potential of ambient vibration techniques to map the 3-D roof morphology of shallow salt diapirs. Horizontal-to-vertical (H/V) spectral peaks are derived at more than 900 positions above a shallow diapir beneath the city area of Hamburg, Germany, and are used to infer the depth of the first strong impedance contrast. In addition, 15 small-scale array measurements are conducted at different positions in order to compute frequency-dependent phase velocities of Rayleigh waves between 0.5 and 25 Hz. The dispersion curves are inverted together with the H/V peak frequency to obtain shear-wave velocity profiles. Additionally, we compare the morphology derived from H/V and array measurements to borehole lithology and a gravity-based 3-D model of the salt diapir. Both methods give consistent results in agreement with major features indicated by the independent data. An important result is that H/V and array measurements are better suited to identify weathered gypsum caprocks or gypsum floaters, while gravity-derived models better sample the interface between sediments and homogeneous salt. We further investigate qualitatively the influence of the 3-D subsurface topography of the salt diapir on the validity of local 1-D inversion results from ambient vibration dispersion curve inversion.
KW  - Ambient seismic vibrations
KW  - H/V method
KW  - Array measurements
KW  - Salt diapir
KW  - 3-D effects
Y1  - 2011
U6  - https://doi.org/10.1007/s10950-011-9234-y
SN  - 1383-4649
VL  - 15
IS  - 3
SP  - 507
EP  - 531
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Krüger, Frank
A1  - Dahm, Torsten
A1  - Hannemann, Katrin
T1  - Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array
JF  - Geophysical journal international
N2  - A mid-aperture broad-band test array (OBS array DOCTAR) was deployed from June 2011 to April 2012 about 100 km north of the Gloria fault in the Eastern North Atlantic in about 5000 m water depth. In addition arrays were installed on Madeira Island and in western Portugal mainland. For the first time in the Eastern North Atlantic, we recorded a large number of high frequency Po and So waves from local and regional small and moderate earthquakes (M-L < 4). An incoherent beamforming method was adapted to scan continuous data for such Po and So arrivals applying a sliding window waveform migration and frequency-wavenumber technique. We identify about 320 Po and 1550 So arrivals and compare the phase onsets with the ISC catalogue (ISC 2015) for the same time span. Up to a distance of 6 degrees to the DOCTAR stations all events listed in the ISC catalogue could be associated to Po and So phases. Arrivals from events in more than 10 degrees distance could be identified only in some cases. Only few Po and/or So arrivals were detected for earthquakes from the European and African continental area, the continental shelf regions and for earthquakes within or northwest of the Azores plateau. Unexpectedly, earthquake clusters are detected within the oceanic plates north and south of the Gloria fault and far from plate boundaries, indicating active intraplate structures. We also observe and locate numerous small magnitude earthquakes on the segment of the Gloria fault directly south of DOCTAR, which likely coincides with the rupture of the 25 November 1941 event. Local small magnitude earthquakes located beneath DOCTAR show hypocentres up to 30 km depth and strike-slip focal mechanisms. A comparison with detections at temporary mid-aperture arrays on Madeira and in western Portugal shows that the deep ocean array performs much better than the island and the continental array regarding the detection threshold for events in the oceanic plates. 
 We conclude that sparsely distributed mid-aperture seismic arrays in the deep ocean could decrease the detection and location threshold for seismicity with M-L < 4 in the oceanic plate and might constitute a valuable tool to monitor oceanic plate seismicity.
KW  - body waves
KW  - earthquake source observations
KW  - seismicity and tectonics
Y1  - 2020
U6  - https://doi.org/10.1093/gji/ggaa054
SN  - 0956-540X
SN  - 1365-246X
VL  - 221
IS  - 2
SP  - 1055
EP  - 1080
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Krüger, Frank
A1  - Dahm, Torsten
T1  - Higher degree moment inversin using far-field broad-band recordings : theory and evaluation of the method with application to the 1994 Bolivia deep earthauke
Y1  - 1999
ER  - 
TY  - GEN
A1  - Kriegerowski, Marius
A1  - Cesca, Simone
A1  - Ohrnberger, Matthias
A1  - Dahm, Torsten
A1  - Krüger, Frank
T1  - Event couple spectral ratio Q method for earthquake clusters
BT  - application to northwest Bohemia
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q-1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high-frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wave-field seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to northwest Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp < 100. The application to S phases fails due to scattered P-phase energy interfering with S phases. The Qp anomaly supports the common hypothesis of highly fractured and fluid saturated rocks in the source region of the swarms in northwest Bohemia. However, high temperatures in a small volume around the swarms cannot be excluded to explain our observations.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 683 
KW  - west bohemia
KW  - attenuation tomography
KW  - swarm earthquakes
KW  - focal zone
KW  - parameters
KW  - locations
KW  - fault
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-426029
IS  - 683
ER  - 
TY  - JOUR
A1  - Kriegerowski, Marius
A1  - Cesca, Simone
A1  - Ohrnberger, Matthias
A1  - Dahm, Torsten
A1  - Krüger, Frank
T1  - Event couple spectral ratio Q method for earthquake clusters
BT  - application to northwest Bohemia
JF  - Solid Earth
N2  - We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (Q-1) in the source volume. The method allows to study attenuation within the source region of earthquake swarms or aftershocks at depth, independent of wave path and attenuation between source region and surface station. We exploit the high-frequency slope of phase spectra using multitaper spectral estimates. The method is tested using simulated full wave-field seismograms affected by recorded noise and finite source rupture. The synthetic tests verify the approach and show that solutions are independent of focal mechanisms but also show that seismic noise may broaden the scatter of results. We apply the event couple spectral ratio method to northwest Bohemia, Czech Republic, a region characterized by the persistent occurrence of earthquake swarms in a confined source region at mid-crustal depth. Our method indicates a strong anomaly of high attenuation in the source region of the swarm with an averaged attenuation factor of Qp < 100. The application to S phases fails due to scattered P-phase energy interfering with S phases. The Qp anomaly supports the common hypothesis of highly fractured and fluid saturated rocks in the source region of the swarms in northwest Bohemia. However, high temperatures in a small volume around the swarms cannot be excluded to explain our observations.
KW  - west bohemia
KW  - attenuation tomography
KW  - swarm earthquakes
KW  - focal zone
KW  - parameters
KW  - locations
KW  - fault
Y1  - 2019
U6  - https://doi.org/10.5194/se-10-317-2019
SN  - 1869-9529
IS  - 10
SP  - 317
EP  - 328
PB  - Copernicus Publications
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Kottmeier, Christoph
A1  - Agnon, Amotz
A1  - Al-Halbouni, Djamil
A1  - Alpert, Pinhas
A1  - Corsmeier, Ulrich
A1  - Dahm, Torsten
A1  - Eshel, Adam
A1  - Geyer, Stefan
A1  - Haas, Michael
A1  - Holohan, Eoghan
A1  - Kalthoff, Norbert
A1  - Kishcha, Pavel
A1  - Krawczyk, Charlotte
A1  - Lati, Joseph
A1  - Laronne, Jonathan B.
A1  - Lott, Friederike
A1  - Mallast, Ulf
A1  - Merz, Ralf
A1  - Metzger, Jutta
A1  - Mohsen, Ayman
A1  - Morin, Efrat
A1  - Nied, Manuela
A1  - Roediger, Tino
A1  - Salameh, Elias
A1  - Sawarieh, Ali
A1  - Shannak, Benbella
A1  - Siebert, Christian
A1  - Weber, Michael
T1  - New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project
JF  - The science of the total environment : an international journal for scientific research into the environment and its relationship with man
N2  - The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, similar to 1 m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments. (C) 2015 The Authors. Published by Elsevier B.V.
KW  - Climate
KW  - Water balance
KW  - Flash floods
KW  - Seismicity
KW  - Sinkholes
KW  - Education
Y1  - 2016
U6  - https://doi.org/10.1016/j.scitotenv.2015.12.003
SN  - 0048-9697
SN  - 1879-1026
VL  - 544
SP  - 1045
EP  - 1058
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Karamzadeh Toularoud, Nasim
A1  - Heimann, Sebastian
A1  - Dahm, Torsten
A1  - Krüger, Frank
T1  - Application based seismological array design by seismicity scenario modelling
JF  - Geophysical journal international
N2  - The design of an array configuration is an important task in array seismology during experiment planning. Often the array response function (ARF), which depends on the relative position of array stations and frequency content of the incoming signals, is used as the array design criterion. In practice, additional constraints and parameters have to be taken into account, for example, land ownership, site-specific noise levels or characteristics of the seismic sources under investigation. In this study, a flexible array design framework is introduced that implements a customizable scenario modelling and optimization scheme by making use of synthetic seismograms. Using synthetic seismograms to evaluate array performance makes it possible to consider additional constraints. We suggest to use synthetic array beamforming as an array design criterion instead of the ARF. The objective function of the optimization scheme is defined according to the monitoring goals, and may consist of a number of subfunctions. The array design framework is exemplified by designing a seven-station small-scale array to monitor earthquake swarm activity in Northwest Bohemia/Vogtland in central Europe. Two subfunctions are introduced to verify the accuracy of horizontal slowness estimation; one to suppress aliasing effects due to possible secondary lobes of synthetic array beamforming calculated in horizontal slowness space and the other to reduce the event’s mislocation caused by miscalculation of the horizontal slowness vector. Subsequently, a weighting technique is applied to combine the subfunctions into one single scalar objective function to use in the optimization process.
KW  - Array Seismology
KW  - Array design
KW  - Seismicity modelling
Y1  - 2018
SN  - 0956-540X
SN  - 1365-246X
VL  - 216
IS  - 3
SP  - 1711
EP  - 1727
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Karamzadeh Toularoud, Nasim
A1  - Heimann, Sebastian
A1  - Dahm, Torsten
A1  - Krüger, Frank
T1  - Earthquake source arrays
BT  - optimal configuration and applications in crustal structure studies
JF  - Geophysical journal international
N2  - A collection of earthquake sources recorded at a single station, under specific conditions, are considered as a source array (SA), that is interpreted as if earthquake sources originate at the station location and are recorded at the source location. Then, array processing methods, that is array beamforming, are applicable to analyse the recorded signals. A possible application is to use source array multiple event techniques to locate and characterize near-source scatterers and structural interfaces. In this work the aim is to facilitate the use of earthquake source arrays by presenting an automatic search algorithm to configure the source array elements. We developed a procedure to search for an optimal source array element distribution given an earthquake catalogue including accurate origin time and hypocentre locations. The objective function of the optimization process can be flexibly defined for each application to ensure the prerequisites (criteria) of making a source array. We formulated four quantitative criteria as subfunctions and used the weighted sum technique to combine them in one single scalar function. The criteria are: (1) to control the accuracy of the slowness vector estimation using the time domain beamforming method, (2) to measure the waveform coherency of the array elements, (3) to select events with lower location error and (4) to select traces with high energy of specific phases, that is, sp- or ps-phases. The proposed procedure is verified using synthetic data as well as real examples for the Vogtland region in Northwest Bohemia. We discussed the possible application of the optimized source arrays to identify the location of scatterers in the velocity model by presenting a synthetic test and an example using real waveforms.
KW  - location of scatterers
KW  - optimization
KW  - source array design
Y1  - 2020
U6  - https://doi.org/10.1093/gji/ggaa002
SN  - 0956-540X
SN  - 1365-246X
VL  - 221
IS  - 1
SP  - 352
EP  - 370
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Karamzadeh, Nasim Toularoud
A1  - Kühn, Daniela
A1  - Kriegerowski, Marius
A1  - López-Comino, José Ángel
A1  - Cesca, Simone
A1  - Dahm, Torsten
T1  - Small-aperture array as a tool to monitor fluid injection- and extraction-induced microseismicity
BT  - applications and recommendations
JF  - Acta Geophysica
N2  - The monitoring of microseismicity during temporary human activities such as fluid injections for hydrofracturing, hydrothermal stimulations or wastewater disposal is a difficult task. The seismic stations often cannot be installed on hard rock, and at quiet places, noise is strongly increased during the operation itself and the installation of sensors in deep wells is costly and often not feasible. The combination of small-aperture seismic arrays with shallow borehole sensors offers a solution. We tested this monitoring approach at two different sites: (1) accompanying a fracking experiment in sedimentary shale at 4km depth and (2) above a gas field under depletion. The small-aperture arrays were planned according to theoretical wavenumber studies combined with simulations considering the local noise conditions. We compared array recordings with recordings available from shallow borehole sensors and give examples of detection and location performance. Although the high-frequency noise on the 50-m-deep borehole sensors was smaller compared to the surface noise before the injection experiment, the signals were highly contaminated during injection by the pumping activities. Therefore, a set of three small-aperture arrays at different azimuths was more suited to detect small events, since noise recorded on these arrays is uncorrelated with each other. Further, we developed recommendations for the adaptation of the monitoring concept to other sites experiencing induced seismicity.
KW  - Microseismic monitoring
KW  - Induced seismicity
KW  - Array seismology
KW  - Shallow borehole sensors
Y1  - 2019
U6  - https://doi.org/10.1007/s11600-018-0231-1
SN  - 1895-6572
SN  - 1895-7455
VL  - 67
IS  - 1
SP  - 311
EP  - 326
PB  - Springer
CY  - Cham
ER  - 
TY  - JOUR
A1  - Jamalreyhani, Mohammadreza
A1  - Rezapour, Mehdi
A1  - Cesca, Simone
A1  - Dahm, Torsten
A1  - Heimann, Sebastian
A1  - Sudhaus, Henriette
A1  - Isken, Marius Paul
T1  - Insight into the 2017-2019 Lurestan arc seismic sequence (Zagros, Iran); complex earthquake interaction in the basement and sediments
JF  - Geophysical journal international
N2  - Despite its high-seismogenic potential, the details of the seismogenic processes of Zagros Simply Folded Belt (SFB) remains debated. Three large earthquakes (M-w 7.3, 5.9 and 6.3) struck in the Lurestan arc of the Zagros SFB in 2017 and 2018. The sequence was recorded by seismic stations at regional, and teleseismic distances. Coseismic surface displacements, measured by Sentinel-1A/B satellites, provide additional data and a unique opportunity to study these earthquakes in detail. Here, we complement previous studies of the coseismic slip distribution of the 12 November 2017 M-w 7.3 Ezgeleh earthquake by a detailed analysis of its aftershocks, and we analysed the rupture process of the two interrelated earthquakes (25 August 2018 M-w 5.9 Tazehabad and the 25 November 2018 M-w 6.3 Sarpol-e Zahab earthquakes). We model the surface displacements obtained from Interferometric Synthetic Aperture Radar (InSAR) measurements and seismic records. We conduct non-linear probabilistic optimizations based on joint InSAR and seismic data to obtain finite-fault rupture of these earthquakes. The Lurestan arc earthquakes were followed by a sustained aftershock activity, with 133 aftershocks exceeding M-n 4.0 until 30 December 2019. We rely on the permanent seismic networks of Iran and Iraq to relocate similar to 700 M-n 3 + events and estimate moment tensor solutions for 85 aftershocks down to M-w 4.0. The 2017 Ezgeleh earthquake has been considered to activate a low-angle (similar to 17 degrees) dextral-thrust fault at the depth of 10-20 km. However, most of its aftershocks have shallow centroid depths (8-12 km). The joint interpretation of finite source models, moment tensor and hypocentral location indicate that the 2018 Tazehabad and Sarpol-e Zahab earthquakes ruptured different strike-slip structures, providing evidence for the activation of the sinistral and dextral strike-slip faults, respectively. The deformation in the Lurestan arc is seismically accommodated by a complex fault system involving both thrust and strike-slip faults. Knowledge about the deformation characteristics is important for the understanding of crustal shortening, faulting and hazard and risk assessment in this region.
KW  - Joint Inversion
KW  - Waveform inversion
KW  - Earthquake source observations
KW  - Seismicity and tectonics
Y1  - 2022
U6  - https://doi.org/10.1093/gji/ggac057
SN  - 0956-540X
SN  - 1365-246X
VL  - 230
IS  - 1
SP  - 114
EP  - 130
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Isken, Marius Paul
A1  - Vasyura-Bathke, Hannes
A1  - Dahm, Torsten
A1  - Heimann, Sebastian
T1  - De-noising distributed acoustic sensing data using an adaptive frequency-wavenumber filter
JF  - Geophysical journal international
N2  - Data recorded by distributed acoustic sensing (DAS) along an optical fibre sample the spatial and temporal properties of seismic wavefields at high spatial density. Often leading to massive amount of data when collected for seismic monitoring along many kilometre long cables. The spatially coherent signals from weak seismic arrivals within the data are often obscured by incoherent noise. We present a flexible and computationally efficient filtering technique, which makes use of the dense spatial and temporal sampling of the data and that can handle the large amount of data. The presented adaptive frequency-wavenumber filter suppresses the incoherent seismic noise while amplifying the coherent wavefield. We analyse the response of the filter in time and spectral domain, and we demonstrate its performance on a noisy data set that was recorded in a vertical borehole observatory showing active and passive seismic phase arrivals. Lastly, we present a performant open-source software implementation enabling real-time filtering of large DAS data sets.
KW  - Fourier analysis
KW  - Image processing
KW  - Time-series analysis
KW  - Seismic noise
KW  - Distributed acoustic sensing
Y1  - 2022
U6  - https://doi.org/10.1093/gji/ggac229
SN  - 0956-540X
SN  - 1365-246X
VL  - 231
IS  - 2
SP  - 944
EP  - 949
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hensch, Martin
A1  - Dahm, Torsten
A1  - Ritter, Joachim
A1  - Heimann, Sebastian
A1  - Schmidt, Bernd
A1  - Stange, Stefan
A1  - Lehmann, Klaus
T1  - Deep low-frequency earthquakes reveal ongoing magmatic recharge beneath Laacher See Volcano (Eifel, Germany)
JF  - Geophysical journal international
N2  - The occurrence of deep low-frequency (DLF) microearthquakes beneath volcanoes is commonly attributed to mass transport in the volcanic plumbing system and used to infer feeding channels from and into magma reservoirs. The key question is how magmas migrate from depth to the shallow crust and whether magma reservoirs are currently being recharged. For the first time since the improvement of the local seismic networks in the East Eifel region (Rhineland-Palatinate, Germany), we detect and locate recurrent DLF earthquakes in the lower crust and upper mantle beneath the Laacher See Volcano (LSV), using a joint data set of permanent sensors and a temporary deployment. So far, eight DLF earthquake sequences were observed in four distinct clusters between 10 and 40 km depth. These clusters of weak events (M-L< 2) align along an approximately 80. southeast dipping line south of the LSV. Moment tensor solutions of these events have large shear components, and the irregular dispersion and long coda of body waves indicate interaction processes between shear cracks and fluids. We find a rotation of P-axes orientation for shallow tectonic earthquakes compared to DLF events, indicating that the stress field in the depth interval of DLF events might favour a vertical migration of magma or magmatic fluids. The caldera of the LSV was formed by the last major eruption of the East Eifel Volcanic Field only 12.9 kyr ago, fed by a shallow magma chamber at 5-8 km depth and erupting a total magma volume of 6.7 km(3). The observed DLF earthquake activity and continuous volcanic gas emissions around the LSV indicate an active magmatic system, possibly connected with an upper mantle melt zone.
KW  - Waveform inversion
KW  - Volcano seismology
KW  - Magma migration and fragmentation
KW  - Volcano monitoring
Y1  - 2019
U6  - https://doi.org/10.1093/gji/ggy532
SN  - 0956-540X
SN  - 1365-246X
VL  - 216
IS  - 3
SP  - 2025
EP  - 2036
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Heimann, Sebastian
A1  - Vasyura-Bathke, Hannes
A1  - Sudhaus, Henriette
A1  - Isken, Marius Paul
A1  - Kriegerowski, Marius
A1  - Steinberg, Andreas
A1  - Dahm, Torsten
T1  - A Python framework for efficient use of pre-computed Green's functions in seismological and other physical forward and inverse source problems
JF  - Solid earth
N2  - The computation of such synthetic GFs is computationally and operationally demanding. As a consequence, the onthe-fly recalculation of synthetic GFs in each iteration of an optimisation is time-consuming and impractical. Therefore, the pre-calculation and efficient storage of synthetic GFs on a dense grid of source to receiver combinations enables the efficient lookup and utilisation of GFs in time-critical scenarios. We present a Python-based framework and toolkit - Pyrocko-GF - that enables the pre-calculation of synthetic GF stores, which are independent of their numerical calculation method and GF transfer function. The framework aids in the creation of such GF stores by interfacing a suite of established numerical forward modelling codes in seismology (computational back ends). So far, interfaces to back ends for layered Earth model cases have been provided; however, the architecture of Pyrocko-GF is designed to cover back ends for other geometries (e.g. full 3-D heterogeneous media) and other physical quantities (e.g. gravity, pressure, tilt). Therefore, Pyrocko-GF defines an extensible GF storage format suitable for a wide range of GF types, especially handling elasticity and wave propagation problems. The framework assists with visualisations, quality control, and the exchange of GF stores, which is supported through an online platform that provides many pre-calculated GF stores for local, regional, and global studies. The Pyrocko-GF toolkit comes with a well-documented application programming interface (API) for the Python programming language to efficiently facilitate forward modelling of geophysical processes, e.g. synthetic waveforms or static displacements for a wide range of source models.
Y1  - 2019
U6  - https://doi.org/10.5194/se-10-1921-2019
SN  - 1869-9510
SN  - 1869-9529
VL  - 10
IS  - 6
SP  - 1921
EP  - 1935
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Heimann, Sebastian
A1  - Gonzalez, Alvaro
A1  - Wang, Rongjiang
A1  - Cesca, Simone
A1  - Dahm, Torsten
T1  - Seismic characterization of the Chelyabinsk Meteor's terminal explosion
JF  - Seismological research letters
Y1  - 2013
U6  - https://doi.org/10.1785/0220130042
SN  - 0895-0695
VL  - 84
IS  - 6
SP  - 1021
EP  - 1025
PB  - Seismological Society of America
CY  - Albany
ER  - 
TY  - JOUR
A1  - Hannemann, Katrin
A1  - Krüger, Frank
A1  - Dahm, Torsten
A1  - Lange, Dietrich
T1  - Oceanic lithospheric S-wave velocities from the analysis of P-wave polarization at the ocean floor
JF  - Geophysical journal international
N2  - Our knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P-wave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s(-1). The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s(-1). We find a slight increase of the total crustal thickness from similar to 5 to similar to 8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S-wave velocities decrease from values around 5.5 to 4.5 km s(-1) towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S-wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P-wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S-wave velocities for real and synthetic data to estimate S-wave velocity-depth models.
KW  - Time-series analysis
KW  - Body waves
KW  - Theoretical seismology
KW  - Oceanic transform and fracture zone processes
Y1  - 2016
U6  - https://doi.org/10.1093/gji/ggw342
SN  - 0956-540X
SN  - 1365-246X
VL  - 207
SP  - 1796
EP  - 1817
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hannemann, Katrin
A1  - Krüger, Frank
A1  - Dahm, Torsten
A1  - Lange, Dietrich
T1  - Structure of the oceanic lithosphere and upper mantle north of the Gloria Fault in the eastern mid-Atlantic by receiver function analysis
JF  - Journal of geophysical research : Solid earth
N2  - Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (approximate to 1year), resulting in a small number of usable records of teleseismic earthquakes. Here we use OBSs deployed as midaperture array in the deep ocean (4.5-5.5km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beamforming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8km) of oceanic crust. Observations at single stations with thin sediments (300-400m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of approximate to 70-80km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at approximate to 410km and approximate to 660km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam-formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events.
KW  - receiver function
KW  - oceanic lithosphere and mantle
KW  - ocean bottom seismology
Y1  - 2017
U6  - https://doi.org/10.1002/2016JB013582
SN  - 2169-9313
SN  - 2169-9356
VL  - 122
SP  - 7927
EP  - 7950
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Hannemann, Katrin
A1  - Krüger, Frank
A1  - Dahm, Torsten
T1  - Measuring of clock drift rates and static time offsets of ocean bottom stations by means of ambient noise
JF  - Geophysical journal international
N2  - Marine seismology usually relies on temporary deployments of stand alone seismic ocean bottom stations (OBS), which are initialized and synchronized on ship before deployment and re-synchronized and stopped on ship after recovery several months later. In between, the recorder clocks may drift and float at unknown rates. If the clock drifts are large or not linear and cannot be corrected for, seismological applications will be limited to methods not requiring precise common timing. Therefore, for example, array seismological methods, which need very accurate timing between individual stations, would not be applicable for such deployments.
 We use an OBS test-array of 12 stations and 75 km aperture, deployed for 10 months in the deep sea (4.5-5.5 km) of the mid-eastern Atlantic. The experiment was designed to analyse the potential of broad-band array seismology at the seafloor. After recovery, we identified some stations which either show unusual large clock drifts and/or static time offsets by having a large difference between the internal clock and the GPS-signal (skew).
 We test the approach of ambient noise cross-correlation to synchronize clocks of a deep water OBS array with km-scale interstation distances. We show that small drift rates and static time offsets can be resolved on vertical components with a standard technique. Larger clock drifts (several seconds per day) can only be accurately recovered if time windows of one input trace are shifted according to the expected drift between a station pair before the cross-correlation. We validate that the drifts extracted from the seismometer data are linear to first order. The same is valid for most of the hydrophones. Moreover, we were able to determine the clock drift at a station where no skew could be measured. Furthermore, we find that instable apparent drift rates at some hydrophones, which are uncorrelated to the seismometer drift recorded at the same digitizer, indicate a malfunction of the hydrophone.
KW  - Time-series analysis
KW  - Interferometry
KW  - Broad-band seismometers
Y1  - 2014
U6  - https://doi.org/10.1093/gji/ggt434
SN  - 0956-540X
SN  - 1365-246X
VL  - 196
IS  - 2
SP  - 1034
EP  - 1042
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hannemann, Katrin
A1  - Eulenfeld, Tom
A1  - Krüger, Frank
A1  - Dahm, Torsten
T1  - Seismic scattering and absorption of oceanic lithospheric S waves in the Eastern North Atlantic
JF  - Geophysical journal international
N2  - The scattering and absorption of high-frequency seismic waves in the oceanic lithosphere is to date only poorly constrained by observations. Such estimates would not only improve our understanding of the propagation of seismic waves, but also unravel the small-scale nature of the lithosphere and its variability. Our study benefits from two exceptional situations: (1) we deployed over 10 months a mid-aperture seismological array in the central part of the Eastern North Atlantic in 5 km water depth and (2) we could observe in total 340 high-frequency (up to 30 Hz) Po and So arrivals with tens to hundreds of seconds long seismic coda from local and regional earthquakes in a wide range of backazimuths and epicentral distances up to 850 km with a travel path in the oceanic lithosphere. Moreover, the array was located about 100 km north of the Gloria fault, defining the plate boundary between the Eurasian and African plates at this location which also allows an investigation of the influence of an abrupt change in lithospheric age (20 Ma in this case) on seismic waves. The waves travel with velocities indicating upper-mantle material. We use So waves and their coda of pre-selected earthquakes to estimate frequency-dependent seismic scattering and intrinsic attenuation parameters. The estimated scattering attenuation coefficients are between 10(-4) and 4 x 10(-5) m(-1) and are typical for the lithosphere or the upper mantle. Furthermore, the total quality factors for So waves below 5 Hz are between 20 and 500 and are well below estimates from previous modelling for observations in the Pacific Ocean. This implies that the Atlantic Ocean is more attenuative for So waves compared to the Pacific Ocean, which is inline with the expected behaviour for the lithospheric structures resulting from the slower spreading rates in the Atlantic Ocean. The results for the analysed events indicate that for frequencies above 3 Hz, intrinsic attenuation is equal to or slightly stronger than scattering attenuation and that the So-wave coda is weakly influenced by the oceanic crust. Both observations are in agreement with the proposed propagation mechanism of scattering in the oceanic mantle lithosphere. Furthermore, we observe an age dependence which shows that an increase in lithospheric age is associated with a decrease in attenuation. However, we also observe a trade-off of this age-dependent effect with either a change in lithospheric thickness or thermal variations, for example due to small-scale upwellings in the upper mantle in the southeast close to Madeira and the Canaries. Moreover, the influence of the nearby Gloria fault is visible in a reduction of the intrinsic attenuation below 3 Hz for estimates across the fault. This is the first study to estimate seismic scattering and absorption parameters of So waves for an area with several hundreds of kilometres radius centred in the Eastern North Atlantic and using them to characterize the nature of the oceanic lithosphere.
KW  - Body waves
KW  - Seismic attenuation
KW  - Wave scattering and diffraction
Y1  - 2021
U6  - https://doi.org/10.1093/gji/ggab493
SN  - 0956-540X
SN  - 1365-246X
VL  - 229
IS  - 2
SP  - 948
EP  - 961
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Grigoli, Francesco
A1  - Cesca, Simone
A1  - Vassallo, Maurizio
A1  - Dahm, Torsten
T1  - Automated seismic event location by travel-time stacking an application to mining induced seismicity
JF  - Seismological research letters
Y1  - 2013
U6  - https://doi.org/10.1785/0220120191
SN  - 0895-0695
VL  - 84
IS  - 4
SP  - 666
EP  - 677
PB  - Seismological Society of America
CY  - Albany
ER  - 
TY  - JOUR
A1  - Grigoli, Francesco
A1  - Cesca, Simone
A1  - Rinaldi, Antonio Pio
A1  - Manconi, Andrea
A1  - Lopez-Comino, José Ángel
A1  - Clinton, John F.
A1  - Westaway, Rob
A1  - Cauzzi, Carlo
A1  - Dahm, Torsten
A1  - Wiemer, Stefan
T1  - The November 2017 M-w 5.5 Pohang earthquake
BT  - a possible case of induced seismicity in South Korea
JF  - Science
N2  - The moment magnitude (M-w) 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area.
Y1  - 2018
U6  - https://doi.org/10.1126/science.aat2010
SN  - 0036-8075
SN  - 1095-9203
VL  - 360
IS  - 6392
SP  - 1003
EP  - 1006
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Grigoli, Francesco
A1  - Cesca, Simone
A1  - Amoroso, Ortensia
A1  - Emolo, Antonio
A1  - Zollo, Aldo
A1  - Dahm, Torsten
T1  - Automated seismic event location by waveform coherence analysis
JF  - Geophysical journal international
N2  - Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterized by low signal-to-noise ratio, automated location methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this paper, we propose a picking free earthquake location method based on the use of the short-term-average/long-term-average (STA/LTA) traces at different stations as observed data. For the P phases, we use the STA/LTA traces of the vertical energy function, whereas for the S phases, we use the STA/LTA traces of a second characteristic function, which is obtained using the principal component analysis technique. In order to locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a 3-D grid, we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event. A pilot application was performed in the Campania-Lucania region (southern Italy) using a seismic network (Irpinia Seismic Network) with an aperture of about 150 km. We located 196 crustal earthquakes (depth < 20 km) with magnitude range 1.1 < M-L < 2.7. A subset of these locations were compared with accurate manual locations refined by using a double-difference technique. Our results indicate a good agreement with manual locations. Moreover, our method is noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals.
KW  - Time-series analysis
KW  - Inverse theory
KW  - Earthquake source observations
KW  - Seismicity and tectonics
KW  - Early warning
Y1  - 2014
U6  - https://doi.org/10.1093/gji/ggt477
SN  - 0956-540X
SN  - 1365-246X
VL  - 196
IS  - 3
SP  - 1742
EP  - 1753
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Fischer, Tomáš
A1  - Hrubcova, Pavla
A1  - Dahm, Torsten
A1  - Woith, Heiko
A1  - Vylita, Tomáš
A1  - Ohrnberger, Matthias
A1  - Vlček, Josef
A1  - Horalek, Josef
A1  - Dedecek, Petr
A1  - Zimmer, Martin
A1  - Lipus, Martin P.
A1  - Pierdominici, Simona
A1  - Kallmeyer, Jens
A1  - Krüger, Frank
A1  - Hannemann, Katrin
A1  - Korn, Michael
A1  - Kaempf, Horst
A1  - Reinsch, Thomas
A1  - Klicpera, Jakub
A1  - Vollmer, Daniel
A1  - Daskalopoulou, Kyriaki
T1  - ICDP drilling of the Eger Rift observatory
BT  - magmatic fluids driving the earthquake swarms and deep biosphere
JF  - Scientific drilling : reports on deep earth sampling and monitoring
N2  - The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere.

This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia–Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Nový Kostel seismogenic zone, borehole F3 in the Hartoušov mofette field and borehole S4 in the newly discovered Bažina maar near Libá. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartoušov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity.
Y1  - 2022
U6  - https://doi.org/10.5194/sd-31-31-2022
SN  - 1816-8957
SN  - 1816-3459
VL  - 31
SP  - 31
EP  - 49
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Fischer, Tomas
A1  - Hrubcova, Pavla
A1  - Dahm, Torsten
A1  - Woith, Heiko
A1  - Vylita, Tomas
A1  - Ohrnberger, Matthias
A1  - Vlcek, Josef
A1  - Horalek, Josef
A1  - Dedecek, Petr
A1  - Zimmer, Martin
A1  - Lipus, Martin P.
A1  - Pierdominici, Simona
A1  - Kallmeyer, Jens
A1  - Krüger, Frank
A1  - Hannemann, Katrin
A1  - Korn, Michael
A1  - Kämpf, Horst
A1  - Reinsch, Thomas
A1  - Klicpera, Jakub
A1  - Vollmer, Daniel
A1  - Daskalopoulou, Kyriaki
T1  - ICDP drilling of the Eger Rift observatory
BT  - magmatic fluids driving the earthquake swarms and deep biosphere
JF  - Scientific Drilling
N2  - The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere. 
This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia-Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Novy Kostel seismogenic zone, borehole F3 in the Hartousov mofette field and borehole S4 in the newly discovered Bazina maar near Liba. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartousov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity.
Y1  - 2022
U6  - https://doi.org/10.5194/sd-31-31-2022
SN  - 1816-8957
SN  - 1816-3459
VL  - 31
SP  - 31
EP  - 49
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Eibl, Eva P. S.
A1  - Müller, Daniel
A1  - Walter, Thomas R.
A1  - Allahbakhshi, Masoud
A1  - Jousset, Philippe
A1  - Hersir, Gylfi Páll
A1  - Dahm, Torsten
T1  - Eruptive cycle and bubble trap of Strokkur Geyser, Iceland
JF  - Journal of geophysical research : JGR. B: Solid earth
N2  - The eruption frequency of geysers can be studied easily on the surface. However, details of the internal structure including possible water and gas filled chambers feeding eruptions and the driving mechanisms often remain elusive. We used a multidisciplinary network of seismometers, video cameras, water pressure sensors and one tiltmeter to study the eruptive cycle, internal structure, and mechanisms driving the eruptive cycle of Strokkur geyser in June 2018. An eruptive cycle at Strokkur always consists of four phases: (1) Eruption, (2) post-eruptive conduit refilling, (3) gas filling of the bubble trap, and (4) regular bubble collapse at shallow depth in the conduit. For a typical single eruption 19 +/- 4 bubble collapses occur in Phase 3 and 8 +/- 2 collapses in Phase 4 at a mean spacing of 1.52 +/- 0.29 and 24.5 +/- 5.9 s, respectively. These collapses release latent heat to the fluid in the bubble trap (Phase 3) and later to the fluid in the conduit (Phase 4). The latter eventually reaches thermodynamic conditions for an eruption. Single to sextuple eruptions have similar spacings between bubble collapses and are likely fed from the same bubble trap at 23.7 +/- 4.4 m depth, 13-23 m west of the conduit. However, the duration of the eruption and recharging phase linearly increases likely due to a larger water, gas and heat loss from the system. Our tremor data provides documented evidence for a bubble trap beneath a pool geyser.
KW  - bubble trap
KW  - eruptive cycle
KW  - geyser
KW  - hydrothermal systems
KW  - source
KW  - location
KW  - tremor
Y1  - 2021
U6  - https://doi.org/10.1029/2020JB020769
SN  - 2169-9313
SN  - 2169-9356
VL  - 126
IS  - 4
PB  - Wiley
CY  - Hoboken, NJ
ER  - 
TY  - JOUR
A1  - Eibl, Eva P. S.
A1  - Hainzl, Sebastian
A1  - Vesely, Nele I. K.
A1  - Walter, Thomas R.
A1  - Jousset, Philippe
A1  - Hersir, Gylfi Pall
A1  - Dahm, Torsten
T1  - Eruption interval monitoring at strokkur Geyser, Iceland
JF  - Geophysical research letters
N2  - Geysers are hot springs whose frequency of water eruptions remain poorly understood. We set up a local broadband seismic network for 1 year at Strokkur geyser, Iceland, and developed an unprecedented catalog of 73,466 eruptions. We detected 50,135 single eruptions but find that the geyser is also characterized by sets of up to six eruptions in quick succession. The number of single to sextuple eruptions exponentially decreased, while the mean waiting time after an eruption linearly increased (3.7 to 16.4 min). While secondary eruptions within double to sextuple eruptions have a smaller mean seismic amplitude, the amplitude of the first eruption is comparable for all eruption types. We statistically model the eruption frequency assuming discharges proportional to the eruption multiplicity and a constant probability for subsequent events within a multituple eruption. The waiting time after an eruption is predictable but not the type or amplitude of the next one. <br /> Plain Language Summary Geysers are springs that often erupt in hot water fountains. They erupt more often than volcanoes but are quite similar. Nevertheless, it is poorly understood how often volcanoes and also geysers erupt. We created a list of 73,466 eruption times of Strokkur geyser, Iceland, from 1 year of seismic data. The geyser erupted one to six times in quick succession. We found 50,135 single eruptions but only 1 sextuple eruption, while the mean waiting time increased from 3.7 min after single eruptions to 16.4 min after sextuple eruptions. Mean amplitudes of each eruption type were higher for single eruptions, but all first eruptions in a succession were similar in height. Assuming a constant heat inflow at depth, we can predict the waiting time after an eruption but not the type or amplitude of the next one.
Y1  - 2019
U6  - https://doi.org/10.1029/2019GL085266
SN  - 0094-8276
SN  - 1944-8007
VL  - 47
IS  - 1
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Dahm, Torsten
A1  - Stiller, Manfred
A1  - Mechie, James
A1  - Heimann, Sebastian
A1  - Hensch, Martin
A1  - Woith, Heiko
A1  - Schmidt, Bernd
A1  - Gabriel, Gerald
A1  - Weber, Michael
T1  - Seismological and geophysical signatures of the deep crustal magma systems of the cenozoic volcanic fields Beneath the Eifel, Germany
JF  - Geochemistry, geophysics, geosystems
N2  - The Quaternary volcanic fields of the Eifel (Rhineland-Palatinate, Germany) had their last eruptions less than 13,000 years ago. Recently, deep low-frequency (DLF) earthquakes were detected beneath one of the volcanic fields showing evidence of ongoing magmatic activity in the lower crust and upper mantle. In this work, seismic wide- and steep-angle experiments from 1978/1979 and 1987/1988 are compiled, partially reprocessed and interpreted, together with other data to better determine the location, size, shape, and state of magmatic reservoirs in the Eifel region near the crust-mantle boundary. We discuss seismic evidence for a low-velocity gradient layer from 30-36 km depth, which has developed over a large region under all Quaternary volcanic fields of the Rhenish Massif and can be explained by the presence of partial melts. We show that the DLF earthquakes connect the postulated upper mantle reservoir with the upper crust at a depth of about 8 km, directly below one of the youngest phonolitic volcanic centers in the Eifel, where CO(2)originating from the mantle is massively outgassing. A bright spot in the West Eifel between 6 and 10 km depth represents a Tertiary magma reservoir and is seen as a model for a differentiated reservoir beneath the young phonolitic center today. We find that the distribution of volcanic fields is controlled by the Variscan lithospheric structures and terrane boundaries as a whole, which is reflected by an offset of the Moho depth, a wedge-shaped transparent zone in the lower crust and the system of thrusts over about 120 km length.
KW  - magma reservoirs
KW  - distributed volcanic fields
KW  - reflection seismic
KW  - crustal magma chamber
KW  - deep low-frequency earthquakes
KW  - low velocity zone
Y1  - 2020
U6  - https://doi.org/10.1029/2020GC009062
SN  - 1525-2027
VL  - 21
IS  - 9
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Dahm, Torsten
A1  - Kuehn, Daniela
A1  - Ohrnberger, Matthias
A1  - Kroeger, Jens
A1  - Wiederhold, Helga
A1  - Reuther, Claus-Dieter
A1  - Dehghani, Ali
A1  - Scherbaum, Frank
T1  - Combining geophysical data sets to study the dynamics of shallow evaporites in urban environments : application to Hamburg, Germany
N2  - Shallowly situated evaporites in built-up areas are of relevance for urban and cultural development and hydrological regulation. The hazard of sinkholes, subrosion depressions and gypsum karst is often difficult to evaluate and may quickly change with anthropogenic influence. The geophysical exploration of evaporites in metropolitan areas is often not feasible with active industrial techniques. We collect and combine different passive geophysical data as microgravity, ambient vibrations, deformation and hydrological information to study the roof morphology of shallow evaporites beneath Hamburg, Northern Germany. The application of a novel gravity inversion technique leads to a 3-D depth model of the salt diapir under study. We compare the gravity-based depth model to pseudo-depths from H/V measurements and depth estimates from small-scale seismological array data. While the general range and trend of the diapir roof is consistent, a few anomalous regions are identified where H/V pseudo-depths indicate shallower structures not observed in gravity or array data. These are interpreted by shallow residual caprock floaters and zones of increased porosity. The shallow salt structure clearly correlates with a relative subsidence in the order of 2 mm yr(-1). The combined interpretation of roof morphology, yearly subsidence rates, chemical analyses of groundwater and of hydraulic head in aquifers indicates that the salt diapir beneath Hamburg is subject to significant ongoing dissolution that may possibly affect subrosion depressions, sinkhole distribution and land usage. The combined analysis of passive geophysical data may be exemplary for the study of shallow evaporites beneath other urban areas.
Y1  - 2010
UR  - http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-246X
U6  - https://doi.org/10.1111/j.1365-246X.2010.04521.x
SN  - 0956-540X
ER  - 
TY  - JOUR
A1  - Dahm, Torsten
A1  - Krüger, Frank
A1  - Essen, Heinz-Hermann
A1  - Hensch, Martin
T1  - Historic microseismic data and their relation to the wave-climate in the North Atlantic
N2  - Microseismic data from observatories in Europe, which have been continuously recorded since about 100 years, contain information on the wave-climate in the North Atlantic. They can potentially be used as additional constraints in high-resolution temporal and spatial reconstructions of the storminess and oceanic waveheights in the past. To resolve spatial patterns data from observatories in different regions are needed. While previous recent studies analyzed only few observatory archives and relatively short time ranges, this is a first attempt to process the whole available data archive from different observatories. We correct and compare smoothed microseismic data from different stations and discuss their correlation and possible use for studies of storminess variability. Microseismic amplitudes at four seismic stations in northern Europe show amplitude peaks in 1920 and 1925, a slow decline in amplitudes till the middle of the 1930's followed by a steady increase of amplitudes till about 1990. From 1990 on microseismic amplitudes decrease. We find a good correlation between the average surface wind velocity in the North Atlantic and microseismic amplitudes at inland stations far away from the coast. Coastal stations are more influenced by local swell and are thus potentially useful to recover regional changes in wind and ocean wavefields with time. The study demonstrates that the analysis of microseismic has the potential to assess climate changes during the last 100 years
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Dahm, Torsten
A1  - Heimann, Sebastian
A1  - Metz, Malte
A1  - Isken, Marius Paul
T1  - A self-similar dynamic rupture model based on the simplified wave-rupture analogy
JF  - Geophysical journal international / the Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society
N2  - The investigation of stresses, faults, structure and seismic hazards requires a good understanding and mapping of earthquake rupture and slip. Constraining the finite source of earthquakes from seismic and geodetic waveforms is challenging because the directional effects of the rupture itself are small and dynamic numerical solutions often include a large number of free parameters. The computational effort is large and therefore difficult to use in an exploratory forward modelling or inversion approach. Here, we use a simplified self-similar fracture model with only a few parameters, where the propagation of the fracture front is decoupled from the calculation of the slip. The approximative method is flexible and computationally efficient. We discuss the strengths and limitations of the model with real-case examples of well-studied earthquakes. These include the M-w 8.3 2015 Illapel, Chile, megathrust earthquake at the plate interface of a subduction zone and examples of continental intraplate strike-slip earthquakes like the M-w 7.1 2016 Kumamoto, Japan, multisegment variable slip event or the M-w 7.5 2018 Palu, Indonesia, supershear earthquake. Despite the simplicity of the model, a large number of observational features ranging from different rupture-front isochrones and slip distributions to directional waveform effects or high slip patches are easy to model. The temporal evolution of slip rate and rise time are derived from the incremental growth of the rupture and the stress drop without imposing other constraints. The new model is fast and implemented in the open-source Python seismology toolbox Pyrocko, ready to study the physics of rupture and to be used in finite source inversions.
KW  - Earthquake dynamics
KW  - Earthquake ground motions
KW  - Earthquake hazards
KW  - Earthquake source observations
Y1  - 2021
U6  - https://doi.org/10.1093/gji/ggab045
SN  - 0956-540X
SN  - 1365-246X
VL  - 225
IS  - 3
SP  - 1586
EP  - 1604
PB  - Oxford Univ. Press
CY  - Oxford
ER  -