TY - JOUR A1 - Hendriyana, Andri A1 - Bauer, Klaus A1 - Muksin, Umar A1 - Weber, Michael T1 - AIC-based diffraction stacking for local earthquake locations at the Sumatran Fault (Indonesia) JF - Geophysical journal international N2 - We present a new workflow for the localization of seismic events which is based on a diffraction stacking approach. In order to address the effects from complex source radiation patterns, we suggest to compute diffraction stacking from a characteristic function (CF) instead of stacking the original waveform data. A new CF, which is called in the following mAIC (modified from Akaike Information Criterion) is proposed. We demonstrate that both P- and S-wave onsets can be detected accurately. To avoid cross-talk between P and S waves due to inaccurate velocity models, we separate the P and S waves from the mAIC function by making use of polarization attributes. Then, the final image function is represented by the largest eigenvalue as a result of the covariance analysis between P-and S-image functions. Results from synthetic experiments show that the proposed diffraction stacking provides reliable results. The workflow of the diffraction stacking method was finally applied to local earthquake data from Sumatra, Indonesia. Recordings from a temporary network of 42 stations deployed for nine months around the Tarutung pull-apart basin were analysed. The seismic event locations resulting from the diffraction stacking method align along a segment of the Sumatran Fault. A more complex distribution of seismicity is imaged within and around the Tarutung basin. Two lineaments striking N-S were found in the centre of the Tarutung basin which support independent results from structural geology. KW - Time-series analysis KW - Body waves KW - Computational seismology KW - Earthquake source observations KW - Seismicity and tectonics Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy045 SN - 0956-540X SN - 1365-246X VL - 213 IS - 2 SP - 952 EP - 962 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 - Amoroso, Ortensia A1 - Emolo, Antonio A1 - Zollo, Aldo A1 - Dahm, Torsten T1 - Automated seismic event location by waveform coherence analysis JF - Geophysical journal international N2 - Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterized by low signal-to-noise ratio, automated location methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this paper, we propose a picking free earthquake location method based on the use of the short-term-average/long-term-average (STA/LTA) traces at different stations as observed data. For the P phases, we use the STA/LTA traces of the vertical energy function, whereas for the S phases, we use the STA/LTA traces of a second characteristic function, which is obtained using the principal component analysis technique. In order to locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a 3-D grid, we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event. A pilot application was performed in the Campania-Lucania region (southern Italy) using a seismic network (Irpinia Seismic Network) with an aperture of about 150 km. We located 196 crustal earthquakes (depth < 20 km) with magnitude range 1.1 < M-L < 2.7. A subset of these locations were compared with accurate manual locations refined by using a double-difference technique. Our results indicate a good agreement with manual locations. Moreover, our method is noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals. KW - Time-series analysis KW - Inverse theory KW - Earthquake source observations KW - Seismicity and tectonics KW - Early warning Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggt477 SN - 0956-540X SN - 1365-246X VL - 196 IS - 3 SP - 1742 EP - 1753 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hainzl, Sebastian A1 - Zöller, Gert A1 - Brietzke, Gilbert B. A1 - Hinzen, Klaus-G. T1 - Comparison of deterministic and stochastic earthquake simulators for fault interactions in the Lower Rhine Embayment, Germany JF - Geophysical journal international N2 - Time-dependent probabilistic seismic hazard assessment requires a stochastic description of earthquake occurrences. While short-term seismicity models are well-constrained by observations, the recurrences of characteristic on-fault earthquakes are only derived from theoretical considerations, uncertain palaeo-events or proxy data. Despite the involved uncertainties and complexity, simple statistical models for a quasi-period recurrence of on-fault events are implemented in seismic hazard assessments. To test the applicability of statistical models, such as the Brownian relaxation oscillator or the stress release model, we perform a systematic comparison with deterministic simulations based on rate- and state-dependent friction, high-resolution representations of fault systems and quasi-dynamic rupture propagation. For the specific fault network of the Lower Rhine Embayment, Germany, we run both stochastic and deterministic model simulations based on the same fault geometries and stress interactions. Our results indicate that the stochastic simulators are able to reproduce the first-order characteristics of the major earthquakes on isolated faults as well as for coupled faults with moderate stress interactions. However, we find that all tested statistical models fail to reproduce the characteristics of strongly coupled faults, because multisegment rupturing resulting from a spatiotemporally correlated stress field is underestimated in the stochastic simulators. Our results suggest that stochastic models have to be extended by multirupture probability distributions to provide more reliable results. KW - Earthquake interaction KW - forecasting KW - and prediction KW - Seismicity and tectonics KW - Statistical seismology Y1 - 2013 U6 - https://doi.org/10.1093/gji/ggt271 SN - 0956-540X SN - 1365-246X VL - 195 IS - 1 SP - 684 EP - 694 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lange, Dietrich A1 - Bedford, J. R. A1 - Moreno, M. A1 - Tilmann, F. A1 - Báez, Juan Carlos A1 - Bevis, M. A1 - Krüger, Frank T1 - Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011 JF - Geophysical journal international N2 - We focus on the relation between seismic and total postseismic afterslip following the Maule M-w 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip modelswe showthat seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the 'afterslip to aftershock ratio' (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation. KW - Creep and deformation KW - Earthquake dynamics KW - Seismicity and tectonics KW - Continental margins: convergent Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggu292 SN - 0956-540X SN - 1365-246X VL - 199 IS - 2 SP - 784 EP - 799 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 - Zöller, Gert A1 - Ben-Zion, Yehuda T1 - Large earthquake hazard of the San Jacinto fault zone, CA, from long record of simulated seismicity assimilating the available instrumental and paleoseismic data JF - Pure and applied geophysics N2 - We investigate spatio-temporal properties of earthquake patterns in the San Jacinto fault zone (SJFZ), California, between Cajon Pass and the Superstition Hill Fault, using a long record of simulated seismicity constrained by available seismological and geological data. The model provides an effective realization of a large segmented strike-slip fault zone in a 3D elastic half-space, with heterogeneous distribution of static friction chosen to represent several clear step-overs at the surface. The simulated synthetic catalog reproduces well the basic statistical features of the instrumental seismicity recorded at the SJFZ area since 1981. The model also produces events larger than those included in the short instrumental record, consistent with paleo-earthquakes documented at sites along the SJFZ for the last 1,400 years. The general agreement between the synthetic and observed data allows us to address with the long-simulated seismicity questions related to large earthquakes and expected seismic hazard. The interaction between m a parts per thousand yen 7 events on different sections of the SJFZ is found to be close to random. The hazard associated with m a parts per thousand yen 7 events on the SJFZ increases significantly if the long record of simulated seismicity is taken into account. The model simulations indicate that the recent increased number of observed intermediate SJFZ earthquakes is a robust statistical feature heralding the occurrence of m a parts per thousand yen 7 earthquakes. The hypocenters of the m a parts per thousand yen 5 events in the simulation results move progressively towards the hypocenter of the upcoming m a parts per thousand yen 7 earthquake. KW - Earthquake dynamics KW - Earthquake interaction KW - forecasting KW - prediction KW - Statistical seismology KW - Seismicity and tectonics Y1 - 2014 U6 - https://doi.org/10.1007/s00024-014-0783-1 SN - 0033-4553 SN - 1420-9136 VL - 171 IS - 11 SP - 2955 EP - 2965 PB - Springer CY - Basel ER - TY - JOUR A1 - Letort, Jean A1 - Retailleau, Lise A1 - Boue, Pierre A1 - Radiguet, Mathilde A1 - Gardonio, Blandine A1 - Cotton, Fabrice A1 - Campillo, Michel T1 - Lateral variations of the Guerrero-Oaxaca subduction zone (Mexico) derived from weak seismicity (M(b)3.5+) detected on a single array at teleseismic distance JF - Geophysical journal international N2 - Detections of pP and sP phase arrivals (the so-called depth phases) at teleseismic distance provide one of the best ways to estimate earthquake focal depth, as the P-pP and the P-sP delays are strongly dependent on the depth. Based on a new processing workflow and using a single seismic array at teleseismic distance, we can estimate the depth of clusters of small events down to magnitude M-b 3.5. Our method provides a direct view of the relative variations of the seismicity depth from an active area. This study focuses on the application of this new methodology to study the lateral variations of the Guerrero subduction zone (Mexico) using the Eielson seismic array in Alaska (USA). After denoising the signals, 1232 M-b 3.5 + events were detected, with clear P, pP, sP and PcP arrivals. A high-resolution view of the lateral variations of the depth of the seismicity of the Guerero-Oaxaca area is thus obtained. The seismicity is shown to be mainly clustered along the interface, coherently following the geometry of the plate as constrained by the receiver-function analysis along the Meso America Subduction Experiment profile. From this study, the hypothesis of tears on the western part of Guerrero and the eastern part of Oaxaca are strongly confirmed by dramatic lateral changes in the depth of the earthquake clusters. The presence of these two tears might explain the observed lateral variations in seismicity, which is correlated with the boundaries of the slow slip events. KW - North America KW - Time-series analysis KW - Body waves KW - Earthquake source observations KW - Seismicity and tectonics Y1 - 2018 U6 - https://doi.org/10.1093/gji/ggy035 SN - 0956-540X SN - 1365-246X VL - 213 IS - 2 SP - 1002 EP - 1012 PB - Oxford Univ. Press CY - Oxford ER -