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 - 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 - 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 - 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 - Cesca, Simone A1 - Grigoli, Francesco A1 - Heimann, Sebastian A1 - Dahm, Torsten A1 - Kriegerowski, Marius A1 - Sobiesiak, M. A1 - Tassara, C. A1 - Olcay, M. T1 - The M-w 8.1 2014 Iquique, Chile, seismic sequence: a tale of foreshocks and aftershocks JF - Geophysical journal international N2 - The 2014 April 1, M-w 8.1 Iquique (Chile) earthquake struck in the Northern Chile seismic gap. With a rupture length of less than 200 km, it left unbroken large segments of the former gap. Early studies were able to model the main rupture features but results are ambiguous with respect to the role of aseismic slip and left open questions on the remaining hazard at the Northern Chile gap. A striking observation of the 2014 earthquake has been its extensive preparation phase, with more than 1300 events with magnitude above M-L 3, occurring during the 15 months preceding the main shock. Increasing seismicity rates and observed peak magnitudes accompanied the last three weeks before the main shock. Thanks to the large data sets of regional recordings, we assess the precursor activity, compare foreshocks and aftershocks and model rupture preparation and rupture effects. To tackle inversion challenges for moderate events with an asymmetric network geometry, we use full waveforms techniques to locate events, map the seismicity rate and derive source parameters, obtaining moment tensors for more than 300 events (magnitudes M-w 4.0-8.1) in the period 2013 January 1-2014 April 30. This unique data set of fore- and aftershocks is investigated to distinguish rupture process models and models of strain and stress rotation during an earthquake. Results indicate that the spatial distributions of foreshocks delineated the shallower part of the rupture areas of the main shock and its largest aftershock, well matching the spatial extension of the aftershocks cloud. Most moment tensors correspond to almost pure double couple thrust mechanisms, consistent with the slab orientation. Whereas no significant differences are observed among thrust mechanisms in different areas, nor among thrust foreshocks and aftershocks, the early aftershock sequence is characterized by the presence of normal fault mechanisms, striking parallel to the trench but dipping westward. These events likely occurred in the shallow wedge structure close to the slab interface and are consequence of the increased extensional stress in this region after the largest events. The overall stress inversion result suggests a minor stress rotation after the main shock, but a significant release of the deviatoric stress. The temporal change in the distribution of focal mechanisms can also be explained in terms of the spatial heterogeneity of the stress field: under such interpretation, the potential of a large megathrust earthquake breaking a larger segment offshore Northern Chile remains high. KW - Earthquake source observations KW - South America Y1 - 2016 U6 - https://doi.org/10.1093/gji/ggv544 SN - 0956-540X SN - 1365-246X VL - 204 SP - 1766 EP - 1780 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Cesca, Simone A1 - Grigoli, Francesco A1 - Heimann, Sebastian A1 - Gonzalez, Alvaro A1 - Buforn, Elisa A1 - Maghsoudi, Samira A1 - Blanch, Estefania A1 - Dahm, Torsten T1 - The 2013 September-October seismic sequence offshore Spain: a case of seismicity triggered by gas injection? JF - Geophysical journal international N2 - A spatially localized seismic sequence originated few tens of kilometres offshore the Mediterranean coast of Spain, close to the Ebro river delta, starting on 2013 September 5, and lasting at least until 2013 October. The sequence culminated in a maximal moment magnitude M-w 4.3 earthquake, on 2013 October 1. The most relevant seismogenic feature in the area is the Fosa de Amposta fault system, which includes different strands mapped at different distances to the coast, with a general NE-SW orientation, roughly parallel to the coastline. However, no significant known historical seismicity has involved this fault system in the past. The epicentral region is also located near the offshore platform of the Castor project, where gas is conducted through a pipeline from mainland and where it was recently injected in a depleted oil reservoir, at about 2 km depth. We analyse the temporal evolution of the seismic sequence and use full waveform techniques to derive absolute and relative locations, estimate depths and focal mechanisms for the largest events in the sequence (with magnitude mbLg larger than 3), and compare them to a previous event (2012 April 8, mbLg 3.3) taking place in the same region prior to the gas injection. Moment tensor inversion results show that the overall seismicity in this sequence is characterized by oblique mechanisms with a normal fault component, with a 30A degrees low-dip angle plane oriented NNE-SSW and a subvertical plane oriented NW-SE. The combined analysis of hypocentral location and focal mechanisms could indicate that the seismic sequence corresponds to rupture processes along shallow low-dip surfaces, which could have been triggered by the gas injection in the reservoir, and excludes the activation of the Amposta fault, as its known orientation is inconsistent with focal mechanism results. An alternative scenario includes the iterated triggering of a system of steep faults oriented NW-SE, which were identified by prior marine seismics investigations. KW - Earthquake dynamics KW - Earthquake source observations Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggu172 SN - 0956-540X SN - 1365-246X VL - 198 IS - 2 SP - 941 EP - 953 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 - 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 - Kulikova, Galina A1 - Schurr, Bernd A1 - Krüger, Frank A1 - Brzoska, Elisabeth A1 - Heimann, Sebastian T1 - Source parameters of the Sarez-Pamir earthquake of 1911 February 18 JF - Geophysical journal international N2 - The Ms ∼ 7.7 Sarez-Pamir earthquake of 1911 February 18 is the largest instrumentally recorded earthquake in the Pamir region. It triggered one of the largest landslides of the past century, building a giant natural dam and forming Lake Sarez. As for many strong earthquakes from that time, information about source parameters of the Sarez-Pamir earthquake is limited due to the sparse observations. Here, we present the analysis of analogue seismic records of the Sarez-Pamir earthquake. We have collected, scanned and digitized 26 seismic records from 13 stations worldwide to relocate the epicentre and determine the event's depth (∼26 km) and magnitude (mB7.3 and Ms7.7). The unusually good quality of the digitized waveforms allowed their modelling, revealing an NE-striking sinistral strike-slip focal mechanism in accordance with regional tectonics. The shallow depth and magnitude (Mw7.3) of the earthquake were confirmed. Additionally, we investigated the possible contribution of the landslide to the waveforms and present an alternative source model assuming the landslide and earthquake occurred in close sequence. KW - Earthquake source observations KW - Seismicity and tectonics KW - Body waves KW - Theoretical seismology Y1 - 2016 U6 - https://doi.org/10.1093/gji/ggw069 SN - 0956-540X SN - 1365-246X VL - 205 SP - 1086 EP - 1098 PB - Oxford Univ. Press CY - Oxford 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 - 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 - TY - JOUR A1 - Steinberg, Andreas A1 - Sudhaus, Henriette A1 - Heimann, Sebastian A1 - Krüger, Frank T1 - Sensitivity of InSAR and teleseismic observations to earthquake rupture segmentation JF - Geophysical journal international N2 - Earthquakes often rupture across more than one fault segment. If such rupture segmentation occurs on a significant scale, a simple point-source or one-fault model may not represent the rupture process well. As a consequence earthquake characteristics inferred, based on one-source assumptions, may become systematically wrong. This might have effects on follow-up analyses, for example regional stress field inversions and seismic hazard assessments. While rupture segmentation is evident for most M-w > 7 earthquakes, also smaller ones with 5.5 < M-w < 7 can be segmented. We investigate the sensitivity of globally available data sets to rupture segmentation and their resolution to reliably estimate the mechanisms in presence of segmentation. We focus on the sensitivity of InSAR (Interferometric Synthetic Aperture Radar) data in the static near-field and seismic waveforms in the far-field of the rupture and carry out non-linear and Bayesian optimizations of single-source and two-sources kinematic models (double-couple point sources and finite, rectangular sources) using InSAR and teleseismic waveforms separately. Our case studies comprises of four M-w 6-7 earthquakes: the 2009 L'Aquila and 2016 Amatrice (Italy) and the 2005 and 2008 Zhongba (Tibet) earthquakes. We contrast the data misfits of different source complexity by using the Akaike informational criterion (AIC). We find that the AIC method is well suited for data-driven inferences on significant rupture segmentation for the given data sets. This is based on our observation that an AIC-stated significant improvement of data fit for two-segment models over one-segment models correlates with significantly different mechanisms of the two source segments and their average compared to the single-segment mechanism. We attribute these modelled differences to a sufficient sensitivity of the data to resolve rupture segmentation. Our results show that near-field data are generally more sensitive to rupture segmentation of shallow earthquakes than far-field data but that also teleseismic data can resolve rupture segmentation in the studied magnitude range. We further conclude that a significant difference in the modelled source mechanisms for different segmentations shows that an appropriate choice of model segmentation matters for a robust estimation of source mechanisms. It reduces systematic biases and trade-off and thereby improves the knowledge on the rupture. Our study presents a strategy and method to detect significant rupture segmentation such that an appropriate model complexity can be used in the source mechanism inference. A similar, systematic investigation of earthquakes in the range of M-w 5.5-7 could provide important hazard-relevant statistics on rupture segmentation. In these cases single-source models introduce a systematic bias. Consideration of rupture segmentation therefore matters for a robust estimation of source mechanisms of the studied earthquakes. KW - radar interferometry KW - waveform inversion KW - earthquake source observations Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa351 SN - 0956-540X SN - 1365-246X VL - 223 IS - 2 SP - 875 EP - 907 PB - Oxford Univ. Press CY - Oxford ER -