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 - JOUR A1 - Al-Halbouni, Djamil A1 - Holohan, Eoghan P. A1 - Taheri, Abbas A1 - Schöpfer, Martin P. J. A1 - Emam, Sacha A1 - Dahm, Torsten T1 - Geomechanical modelling of sinkhole development using distinct elements BT - model verification for a single void space and application to the Dead Sea area JF - Solid earth N2 - Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth / diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth / diameter values in each material type may partly reflect sinkhole growth trends. Y1 - 2018 U6 - https://doi.org/10.5194/se-9-1341-2018 SN - 1869-9510 SN - 1869-9529 VL - 9 IS - 6 SP - 1341 EP - 1373 PB - Copernicus CY - Göttingen 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 - 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 - GEN A1 - Al-Halbouni, Djamil A1 - Holohan, Eoghan P. A1 - Taheri, Abbas A1 - Schöpfer, Martin P. J. A1 - Emam, Sacha A1 - Dahm, Torsten T1 - Geomechanical modelling of sinkhole development using distinct elements BT - model verification for a single void space and application to the Dead Sea area T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth ∕ diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth ∕ diameter values in each material type may partly reflect sinkhole growth trends. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1061 KW - rock mass KW - karst KW - dissolution KW - reflection KW - subsidence KW - subrosion KW - collapse KW - simulation KW - scale KW - fault Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-468435 SN - 1866-8372 IS - 1061 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 - Cesca, Simone A1 - Heimann, Sebastian A1 - Kriegerowski, Marius A1 - Saul, Joachim A1 - Dahm, Torsten T1 - Moment tensor inversion for nuclear explosions BT - what can we learn from the 6 January and 9 September 2016 Nuclear Tests, North Korea? JF - Seismological research letters N2 - Two nuclear explosions were carried out by the Democratic People’s Republic of North Korea in January and September 2016. Epicenters were located close to those of the 2006, 2009, and 2013 previous explosions. We perform a seismological analysis of the 2016 events combining the analysis of full waveforms at regional distances and seismic array beams at teleseismic distances. We estimate the most relevant source parameters, such as source depth, moment release, and full moment tensor (MT). The best MT solution can be decomposed into an isotropic source, directly related with the explosion and an additional deviatoric term, likely due to near‐source interactions with topographic and/or underground facilities features. We additionally perform an accurate resolution test to assess source parameters uncertainties and trade‐offs. This analysis sheds light on source parameters inconsistencies among studies on previous shallow explosive sources. The resolution of the true MT is hindered by strong source parameters trade‐offs, so that a broad range of well‐fitting MT solutions can be found, spanning from a dominant positive isotropic term to a dominant negative vertical compensated linear vector dipole. The true mechanism can be discriminated by additionally modeling first‐motion polarities at seismic arrays at teleseismic distances. A comparative assessment of the 2016 explosion with earlier nuclear tests documents similar vertical waveforms but a significant increase of amplitude for the 2016 explosions, which proves that the 9 September 2016 was the largest nuclear explosion ever performed in North Korea with a magnitude Mw 4.9 and a shallow depth of less than 2 km, although there are no proofs of a fusion explosion. Modeling transversal component waveforms suggests variable size and orientation of the double‐couple components of the 2009, 2013, and 2016 sources. Y1 - 2017 U6 - https://doi.org/10.1785/0220160139 SN - 0895-0695 SN - 1938-2057 VL - 88 IS - 2A SP - 300 EP - 310 PB - Seismological Society of America CY - Albany 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 - Dahm, Torsten A1 - Heimann, Sebastian A1 - Funke, Sigward A1 - Wendt, Siegfried A1 - Rappsilber, Ivo A1 - Bindi, Dino A1 - Plenefisch, Thomas A1 - Cotton, Fabrice Pierre T1 - Seismicity in the block mountains between Halle and Leipzig, Central Germany BT - centroid moment tensors, ground motion simulation, and felt intensities of two M approximate to 3 earthquakes in 2015 and 2017 JF - Journal of seismology N2 - On April 29, 2017 at 0:56 UTC (2:56 local time), an M (W) = 2.8 earthquake struck the metropolitan area between Leipzig and Halle, Germany, near the small town of Markranstadt. The earthquake was felt within 50 km from the epicenter and reached a local intensity of I (0) = IV. Already in 2015 and only 15 km northwest of the epicenter, a M (W) = 3.2 earthquake struck the area with a similar large felt radius and I (0) = IV. More than 1.1 million people live in the region, and the unusual occurrence of the two earthquakes led to public attention, because the tectonic activity is unclear and induced earthquakes have occurred in neighboring regions. Historical earthquakes south of Leipzig had estimated magnitudes up to M (W) ae 5 and coincide with NW-SE striking crustal basement faults. We use different seismological methods to analyze the two recent earthquakes and discuss them in the context of the known tectonic structures and historical seismicity. Novel stochastic full waveform simulation and inversion approaches are adapted for the application to weak, local earthquakes, to analyze mechanisms and ground motions and their relation to observed intensities. We find NW-SE striking normal faulting mechanisms for both earthquakes and centroid depths of 26 and 29 km. The earthquakes are located where faults with large vertical offsets of several hundred meters and Hercynian strike have developed since the Mesozoic. We use a stochastic full waveform simulation to explain the local peak ground velocities and calibrate the method to simulate intensities. Since the area is densely populated and has sensitive infrastructure, we simulate scenarios assuming that a 12-km long fault segment between the two recent earthquakes is ruptured and study the impact of rupture parameters on ground motions and expected damage. KW - Deep crustal intraplate seismicity KW - Centroid moment tensor of M approximate to 3 earthquakes KW - Observed and simulated ground motions Y1 - 2018 U6 - https://doi.org/10.1007/s10950-018-9746-9 SN - 1383-4649 SN - 1573-157X VL - 22 IS - 4 SP - 985 EP - 1003 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Dahm, Torsten A1 - Heimann, Sebastian A1 - Funke, Sigward A1 - Wendt, Siegfried A1 - Rappsilber, Ivo A1 - Bindi, Dino A1 - Plenefisch, Thomas A1 - Cotton, Fabrice Pierre T1 - Correction to: Seismicity in the block mountains between Halle and Leipzig, Central Germany: centroid moment tensors, ground motion simulation, and felt intensities of two M approximate to 3 earthquakes in 2015 and 2017 (vol 22, pg 985, 2018) T2 - Journal of seismology Y1 - 2018 U6 - https://doi.org/10.1007/s10950-018-9773-6 SN - 1383-4649 SN - 1573-157X VL - 22 IS - 6 SP - 1669 EP - 1671 PB - Springer CY - Dordrecht ER -