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 - 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.
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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 -