@article{HendriyanaBauerMuksinetal.2018, author = {Hendriyana, Andri and Bauer, Klaus and Muksin, Umar and Weber, Michael}, title = {AIC-based diffraction stacking for local earthquake locations at the Sumatran Fault (Indonesia)}, series = {Geophysical journal international}, volume = {213}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggy045}, pages = {952 -- 962}, year = {2018}, abstract = {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.}, language = {en} } @article{SenCescaBischoffetal.2013, author = {Sen, Ali Tolga and Cesca, Simone and Bischoff, Monika and Meier, Thomas and Dahm, Torsten}, title = {Automated full moment tensor inversion of coal mining-induced seismicity}, series = {Geophysical journal international}, volume = {195}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggt300}, pages = {1267 -- 1281}, year = {2013}, abstract = {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.}, language = {en} } @article{GrigoliCescaAmorosoetal.2014, author = {Grigoli, Francesco and Cesca, Simone and Amoroso, Ortensia and Emolo, Antonio and Zollo, Aldo and Dahm, Torsten}, title = {Automated seismic event location by waveform coherence analysis}, series = {Geophysical journal international}, volume = {196}, journal = {Geophysical journal international}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggt477}, pages = {1742 -- 1753}, year = {2014}, abstract = {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.}, language = {en} } @article{PaloTilmannKruegeretal.2014, author = {Palo, Mauro and Tilmann, Frederik and Kr{\"u}ger, Frank and Ehlert, Lutz and Lange, Dietrich}, title = {High-frequency seismic radiation from Maule earthquake (M-w 8.8, 2010 February 27) inferred from high-resolution backprojection analysis}, series = {Geophysical journal international}, volume = {199}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggu311}, pages = {1058 -- 1077}, year = {2014}, abstract = {We track a bilateral rupture propagation lasting similar to 160 s, with its dominant branch rupturing northeastwards at about 3 kms(-1). The area of maximum energy emission is offset from the maximum coseismic slip but matches the zone where most plate interface aftershocks occur. Along dip, energy is preferentially released from two disconnected interface belts, and a distinct jump from the shallower belt to the deeper one is visible after about 20 s from the onset. However, both belts keep on being active until the end of the rupture. These belts approximately match the position of the interface aftershocks, which are split into two clusters of events at different depths, thus suggesting the existence of a repeated transition from stick-slip to creeping frictional regime.}, language = {en} } @article{MaghsoudiHainzlCescaetal.2014, author = {Maghsoudi, Samira and Hainzl, Sebastian and Cesca, Simone and Dahm, Torsten and Kaiser, Diethelm}, title = {Identification and characterization of growing large-scale en-echelon fractures in a salt mine}, series = {Geophysical journal international}, volume = {196}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggt443}, pages = {1092 -- 1105}, year = {2014}, abstract = {The spatiotemporal seismicity of acoustic emission (AE) events recorded in the Morsleben salt mine is investigated. Almost a year after backfilling of the cavities from 2003, microevents are distributed with distinctive stripe shapes above cavities at different depth levels. The physical forces driving the creation of these stripes are still unknown. This study aims to find the active stripes and track fracture developments over time by combining two different temporal and spatial clustering techniques into a single methodological approach. Anomalous seismicity parameters values like sharp b-value changes for two active stripes are good indicators to explain possible stress accumulation at the stripe tips. We identify the formation of two new seismicity stripes and show that the AE activities in active clusters are migrated mostly unidirectional to eastward and upward. This indicates that the growth of underlying macrofractures is controlled by the gradient of extensional stress. Studying size distribution characteristic in terms of frequency-magnitude distribution and b-value in active phase and phase with constant seismicity rate show that deviations from the Gutenberg-Richter power law can be explained by the inclusion of different activity phases: (1) the inactive period before the formation of macrofractures, which is characterized by a deficit of larger events (higher b-values) and (2) the period of fracture growth characterized by the occurrence of larger events (smaller b-values).}, language = {en} } @article{LetortRetailleauBoueetal.2018, author = {Letort, Jean and Retailleau, Lise and Boue, Pierre and Radiguet, Mathilde and Gardonio, Blandine and Cotton, Fabrice Pierre and Campillo, Michel}, title = {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}, series = {Geophysical journal international}, volume = {213}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggy035}, pages = {1002 -- 1012}, year = {2018}, abstract = {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.}, language = {en} } @article{KruegerKulikovaLandgraf2018, author = {Kr{\"u}ger, Frank and Kulikova, Galina and Landgraf, Angela}, title = {Magnitudes for the historical 1885 (Belovodskoe), the 1887 (Verny) and the 1889 (Chilik) earthquakes in Central Asia determined from magnetogram recordings}, series = {Geophysical journal international}, volume = {215}, journal = {Geophysical journal international}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggy377}, pages = {1824 -- 1840}, year = {2018}, abstract = {Six large magnitude earthquakes in Central Asia which occurred at the end of the 19th century were recorded on early magnetographs in Great Britain. Scalar seismic moment estimates of the 1911 Chon-Kemin, the 1902 Atushi and the 1907 Karatag earthquakes in Central Asia were recently determined by historical seismogram modelling. For those events, we find agreement between moment magnitudes estimated from seismograms and from magnetograms. This supports the assumption of linear scaling of magnetogram amplitudes as function of M-0, which we then use to estimate the moment magnitudes for earlier large-magnitude events, that is, the 1885 Belovodskoe, 1887 Verny and 1889 Chilik earthquakes. The magnetometer data imply that the Chilik earthquake had M(W)7.9, slightly smaller than the Chon-Kemin event with M(W)8.0. The Verny earthquake, however, for which we estimate M(W)7.7, is likely larger than listed in catalogues (M7.3). Similarly, we find a larger magnitude M(W)7.6 (instead of the previous M6.9) for the Belovodskoe earthquake, but this remains uncertain due to measurement imprecision.}, language = {en} } @article{DiGiacomoBindiParolaietal.2011, author = {Di Giacomo, Domenico and Bindi, Dino and Parolai, Stefano and Oth, Adrien}, title = {Residual analysis of teleseismic P-wave energy magnitude estimates: inter- and intrastation variability}, series = {Geophysical journal international}, volume = {185}, journal = {Geophysical journal international}, number = {3}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0956-540X}, doi = {10.1111/j.1365-246X.2011.05019.x}, pages = {1444 -- 1454}, year = {2011}, abstract = {P>Computing the magnitude of an earthquake requires correcting for the propagation effects from the source to the receivers. This is often accomplished by performing numerical simulations using a suitable Earth model. In this work, the energy magnitude M(e) is considered and its determination is performed using theoretical spectral amplitude decay functions over teleseismic distances based on the global Earth model AK135Q. Since the high frequency part (above the corner frequency) of the source spectrum has to be considered in computing M(e), the influence of propagation and site effects may not be negligible and they could bias the single station M(e) estimations. Therefore, in this study we assess the inter- and intrastation distributions of errors by considering the M(e) residuals computed for a large data set of earthquakes recorded at teleseismic distances by seismic stations deployed worldwide. To separate the inter- and intrastation contribution of errors, we apply a maximum likelihood approach to the M(e) residuals. We show that the interstation errors (describing a sort of site effect for a station) are within +/- 0.2 magnitude units for most stations and their spatial distribution reflects the expected lateral variation affecting the velocity and attenuation of the Earth's structure in the uppermost layers, not accounted for by the 1-D AK135Q model. The variance of the intrastation error distribution (describing the record-to-record component of variability) is larger than the interstation one (0.240 against 0.159), and the spatial distribution of the errors is not random but shows specific patterns depending on the source-to-station paths. The set of coefficients empirically determined may be used in the future to account for the heterogeneities of the real Earth not considered in the theoretical calculations of the spectral amplitude decay functions used to correct the recorded data for propagation effects.}, language = {en} } @article{AlinaghiKruger2014, author = {Alinaghi, Alireza and Kruger, Frank}, title = {Seismic array analysis and redetermination of depths of earthquakes in Tien-Shan: implications for strength of the crust and lithosphere}, series = {Geophysical journal international}, volume = {198}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggu141}, pages = {1111 -- 1129}, year = {2014}, abstract = {We have redetermined focal depths of moderate and major earthquakes with reported lower-crust and upper-mantle depths that have occurred in Tien-Shan, since the availability of broad-band array data. Records of earthquakes at global arrays have been used for identification and modelling of depth phases in order to make accurate estimation of focal depths. Our results show that half of the purportedly deep earthquakes are indeed originating from depths attributable to middle-crust and lower-crust regions. Also one exceptional event in the northern foreland of Tien-Shan in Junggar Basin is located in the upper mantle at the depth of 64 km. Such unusually deep earthquakes for intraplate continental tectonic domain are all located at the margin of Tien-Shan with its adjacent stable blocks and at least some of them have occurred where the brittle behaviour of continental rocks is not highly expected. The reverse mechanisms of all these earthquakes and their proximity to formerly subducting and later colliding and underplating stable blocks and their interactions with overlying Tien-Shan are clues to explain this extremity.}, language = {en} } @article{CescaSenDahm2014, author = {Cesca, Simone and Sen, Ali Tolga and Dahm, Torsten}, title = {Seismicity monitoring by cluster analysis of moment tensors}, series = {Geophysical journal international}, volume = {196}, journal = {Geophysical journal international}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggt492}, pages = {1813 -- 1826}, year = {2014}, abstract = {We suggest a new clustering approach to classify focal mechanisms from large moment tensor catalogues, with the purpose of automatically identify families of earthquakes with similar source geometry, recognize the orientation of most active faults, and detect temporal variations of the rupture processes. The approach differs in comparison to waveform similarity methods since clusters are detected even if they occur in large spatial distances. This approach is particularly helpful to analyse large moment tensor catalogues, as in microseismicity applications, where a manual analysis and classification is not feasible. A flexible algorithm is here proposed: it can handle different metrics, norms, and focal mechanism representations. In particular, the method can handle full moment tensor or constrained source model catalogues, for which different metrics are suggested. The method can account for variable uncertainties of different moment tensor components. We verify the method with synthetic catalogues. An application to real data from mining induced seismicity illustrates possible applications of the method and demonstrate the cluster detection and event classification performance with different moment tensor catalogues. Results proof that main earthquake source types occur on spatially separated faults, and that temporal changes in the number and characterization of focal mechanism clusters are detected. We suggest that moment tensor clustering can help assessing time dependent hazard in mines.}, language = {en} }