TY - JOUR A1 - Maghsoudi, Samira A1 - Hainzl, Sebastian A1 - Cesca, Simone A1 - Dahm, Torsten A1 - Kaiser, Diethelm T1 - Identification and characterization of growing large-scale en-echelon fractures in a salt mine JF - Geophysical journal international N2 - 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). KW - Earthquake source observations KW - Statistical seismology Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggt443 SN - 0956-540X SN - 1365-246X VL - 196 IS - 2 SP - 1092 EP - 1105 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 - JOUR A1 - Maghsoudi, Samira A1 - Cesca, Simone A1 - Hainzl, Sebastian A1 - Dahm, Torsten A1 - Zöller, Gert A1 - Kaiser, Diethelm T1 - Maximum Magnitude of Completeness in a Salt Mine JF - Bulletin of the Seismological Society of America N2 - In this study, we analyze acoustic emission (AE) data recorded at the Morsleben salt mine, Germany, to assess the catalog completeness, which plays an important role in any seismicity analysis. We introduce the new concept of a magnitude completeness interval consisting of a maximum magnitude of completeness (M-c(max)) in addition to the well-known minimum magnitude of completeness. This is required to describe the completeness of the catalog, both for the smallest events (for which the detection performance may be low) and for the largest ones (which may be missed because of sensors saturation). We suggest a method to compute the maximum magnitude of completeness and calculate it for a spatial grid based on (1) the prior estimation of saturation magnitude at each sensor, (2) the correction of the detection probability function at each sensor, including a drop in the detection performance when it saturates, and (3) the combination of detection probabilities of all sensors to obtain the network detection performance. The method is tested using about 130,000 AE events recorded in a period of five weeks, with sources confined within a small depth interval, and an example of the spatial distribution of M-c(max) is derived. The comparison between the spatial distribution of M-c(max) and of the maximum possible magnitude (M-max), which is here derived using a recently introduced Bayesian approach, indicates that M-max exceeds M-c(max) in some parts of the mine. This suggests that some large and important events may be missed in the catalog, which could lead to a bias in the hazard evaluation. Y1 - 2015 U6 - https://doi.org/10.1785/0120140039 SN - 0037-1106 SN - 1943-3573 VL - 105 IS - 3 SP - 1491 EP - 1501 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Cesca, Simone A1 - Sen, Ali Tolga A1 - Dahm, Torsten T1 - Seismicity monitoring by cluster analysis of moment tensors JF - Geophysical journal international N2 - 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. KW - Persistence KW - memory KW - correlations KW - clustering KW - Earthquake source observations Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggt492 SN - 0956-540X SN - 1365-246X VL - 196 IS - 3 SP - 1813 EP - 1826 PB - Oxford Univ. Press CY - Oxford ER - TY - GEN A1 - Dahm, Torsten A1 - Becker, Dirk A1 - Bischoff, Monika A1 - Cesca, Simone A1 - Dost, B. A1 - Fritschen, R. A1 - Hainzl, Sebastian A1 - Klose, C. D. A1 - Kuhn, D. A1 - Lasocki, S. A1 - Meier, Thomas A1 - Ohrnberger, Matthias A1 - Rivalta, Eleonora A1 - Wegler, Ulrich A1 - Husen, Stephan T1 - Recommendation for the discrimination of human-related and natural seismicity T2 - Journal of seismology N2 - Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology. KW - Triggered seismicity KW - Induced seismicity Y1 - 2013 U6 - https://doi.org/10.1007/s10950-012-9295-6 SN - 1383-4649 VL - 17 IS - 1 SP - 197 EP - 202 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Kottmeier, Christoph A1 - Agnon, Amotz A1 - Al-Halbouni, Djamil A1 - Alpert, Pinhas A1 - Corsmeier, Ulrich A1 - Dahm, Torsten A1 - Eshel, Adam A1 - Geyer, Stefan A1 - Haas, Michael A1 - Holohan, Eoghan A1 - Kalthoff, Norbert A1 - Kishcha, Pavel A1 - Krawczyk, Charlotte A1 - Lati, Joseph A1 - Laronne, Jonathan B. A1 - Lott, Friederike A1 - Mallast, Ulf A1 - Merz, Ralf A1 - Metzger, Jutta A1 - Mohsen, Ayman A1 - Morin, Efrat A1 - Nied, Manuela A1 - Roediger, Tino A1 - Salameh, Elias A1 - Sawarieh, Ali A1 - Shannak, Benbella A1 - Siebert, Christian A1 - Weber, Michael T1 - New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, similar to 1 m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments. (C) 2015 The Authors. Published by Elsevier B.V. KW - Climate KW - Water balance KW - Flash floods KW - Seismicity KW - Sinkholes KW - Education Y1 - 2016 U6 - https://doi.org/10.1016/j.scitotenv.2015.12.003 SN - 0048-9697 SN - 1879-1026 VL - 544 SP - 1045 EP - 1058 PB - Elsevier CY - Amsterdam 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 - Grigoli, Francesco A1 - Cesca, Simone A1 - Rinaldi, Antonio Pio A1 - Manconi, Andrea A1 - Lopez-Comino, José Ángel A1 - Clinton, John F. A1 - Westaway, Rob A1 - Cauzzi, Carlo A1 - Dahm, Torsten A1 - Wiemer, Stefan T1 - The November 2017 M-w 5.5 Pohang earthquake BT - a possible case of induced seismicity in South Korea JF - Science N2 - The moment magnitude (M-w) 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area. Y1 - 2018 U6 - https://doi.org/10.1126/science.aat2010 SN - 0036-8075 SN - 1095-9203 VL - 360 IS - 6392 SP - 1003 EP - 1006 PB - American Assoc. for the Advancement of Science CY - Washington 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 -