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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 -