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On February 6th, 2023 at 01:17 UTC, a devastating MW 7.8 earthquake nucleated on the Pazarcik segment of the East Anatolian Fault Zone (EAFZ) bounding the Arabian and Anatolian tectonic plates. The fault rupture included nucleation on a secondary fault branch of the EAFZ towards the SE of the main fault and a subsequent rupture propagation towards the NE and SW on the main EAFZ. This event was followed 9 hours later by an Mw 7.5 event on the Sürgü Fault about 100km to the North.We evaluate the regional earthquake catalog provided by the Turkish Disaster and Emergency Management Presidency in the years leading up to the first mainshock and identify an acceleration in seismicity rates and seismic moment release in the very vicinity of the mainshock epicenter a few months before the earthquake in comparison to surrounding areas. First results show that this activity is concentrated in earthquake clusters on the secondary as well as main fault branch exhibiting low b-values around 0.6-0.7.We develop an enhanced event catalog in the surrounding of the earthquake doublet spanning the time interval 01/01/2023-11/02/2023 using the Phasenet package and perform automatic P- and S-wave phase picking. Picks are associated into events using GaMMA software and single event and relative event locations are performed using NLLoc and hypoDD. The resulting enhanced event catalog presents the detailed view of the spatio-temporal evolution of seismic actvity around the mainshock epicenter framing the last stage of the preparatory process and the first few days of aftershock activity., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

On November 23rd 2022, a MW 6.0 earthquake occurred in direct vicinity of the MW 7.1 Düzce earthquake that ruptured a portion of the North Anatolian Fault in 1999. The Mw 6.0 event was attributed to a small fault portion of the Karadere segment that did not rupture during the 1999 sequence. We analyze the spatio-temporal evolution of the MW 6.0 Gölyaka-Düzce seismic sequence at various scales and resolve the source properties of the mainshock. Modelling the decade-long evolution of background seismicity of the Karadere Fault employing an Epistemic Type Aftershock Sequence model shows that this fault was almost seismically inactive before 1999, while a progressive increase in seismic activity is observed from 2000 onwards. A newly generated high-resolution seismicity catalog from 1 month before the mainshock until six days after created using Artificial Intelligence-aided techniques shows only few events occurring within the rupture area within the previous month, no spatio-temporal localization process and a lack of immediate foreshocks preceding the rupture. The aftershock hypocenter distribution suggests the activation of both the Karadere fault which ruptured in this earthquake as well as the Düzce fault that ruptured in 1999. First results on source parameters and the duration of the first P-wave pulse from the mainshock suggest that the mainshock propagated eastwards in agreement with predictions from a bimaterial interface model. The MW 6.0 Gölyaka-Düzce represents a good example of an earthquake rupture with damaging potential within a fault zone that is in a relatively early stage of the seismic cycle., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

We investigate induced seismicity associated with a hydraulic stimulation campaign performed in 2020 in the 5.8 km deep geothermal OTN‐2 well near Helsinki, Finland as part of the St1 Deep Heat project. A total of 2,875 m3 of fresh water was injected during 16 days at well‐head pressures −1.9 ${M}_{\mathrm{L}}^{\mathrm{H}\mathrm{e}\mathrm{l}} > -1.9$ were recorded during and after the stimulation campaign. The analyzed statistical parameters include magnitude‐frequency b‐value, interevent time and interevent time ratio, as well as magnitude correlations. We find that the b‐value remained stationary for the entire injection period suggesting limited stress build‐up or limited fracture network coalescence in the reservoir. The seismicity during the stimulation neither shows signatures of magnitude correlations, nor temporal clustering or anticlustering beyond those arising from varying injection rates. The interevent time statistics are characterized by a Poissonian time‐varying distribution. The calculated parameters indicate no earthquake interaction. Focal mechanisms suggest that the injection activated a spatially distributed network of similarly oriented fractures. The seismicity displays stable behavior with no signatures pointing toward a runaway event. The cumulative seismic moment is proportional to the cumulative hydraulic energy and the maximum magnitude is controlled by injection rate. The performed study provides a base for implementation of time‐dependent probabilistic seismic hazard assessment for the project site., Plain Language Summary: We investigate anthropogenic seismicity associated with fluid injection into the 5.8 km deep geothermal OTN‐2 well near Helsinki, Finland, as a part of St1 Deep Heat Project. A total of 2,875 m3 of fresh water was injected during 16 days at well‐head pressures, Key Points: Induced seismicity associated with stimulation campaign in a 5.8 km deep geothermal OTN‐2 well passively responds to injection operations. Seismicity is a non‐stationary Poisson process with seismicity rate and maximum magnitude modulated by the hydraulic energy input rate. Seismicity clusters in space and time in response to fluid injection but no interaction between earthquakes is observed., Helmholtz Association http://dx.doi.org/10.13039/501100009318, https://doi.org/10.5880/GFZ.4.2.2022.001

Earthquake source parameters such as seismic stress drop and corner frequency are observed to vary widely, leading to persistent discussion on potential scaling of stress drop and event size. Physical mechanisms that govern stress drop variations arc difficult to evaluate in nature and are more readily studied in controlled laboratory experiments. We perform two stick-slip experiments on fractured (rough) and cut (smooth) Westerly granite samples to explore fault roughness effects on acoustic emission (AE) source parameters. We separate large stick-slip events that generally saturate the seismic recording system from populations of smaller AE events which are sensitive to fault stresses prior to slip. AE event populations show many similarities to natural seismicity and may be interpreted as laboratory equivalent of natural microseismic events. We then compare the temporal evolution of mechanical data such as measured stress release during slip to temporal changes in stress drops derived from Alis using the spectral ratio technique. We report on two primary observations: (1) In contrast to most case studies for natural earthquakes, we observe a strong increase in seismic stress drop with AE size. (2) The scaling of stress drop with magnitude is governed by fault roughness, whereby the rough fault shows a more rapid increase of the stress drop magnitude relation with progressing large stick-slip events than the smooth fault. The overall range of AE sizes on the rough surface is influenced by both the average grain size and the width of the fault core. The magnitudes of the smallest AE events on smooth faults may also be governed by grain size. However, AEs significantly grow beyond peak roughness and the width of the fault core. Our laboratory tests highlight that source parameters vary substantially in the presence of fault zone heterogeneity (i.e. roughness and narrow grain size distribution), which may affect seismic energy partitioning and static stress drops of small and large AE events.

Understanding the physical mechanisms governing fluid-induced fault slip is important for improved mitigation of seismic risks associated with large-scale fluid injection. We conducted fluid-induced fault slip experiments in the laboratory on critically stressed saw-cut sandstone samples with high permeability using different fluid pressurization rates. Our experimental results demonstrate that fault slip behavior is governed by fluid pressurization rate rather than injection pressure. Slow stick-slip episodes (peak slip velocity

Near–real-time seismic monitoring and injection control limits induced earthquakes in urban geothermal reservoir stimulation., We show that near–real-time seismic monitoring of fluid injection allowed control of induced earthquakes during the stimulation of a 6.1-km-deep geothermal well near Helsinki, Finland. A total of 18,160 m3 of fresh water was pumped into crystalline rocks over 49 days in June to July 2018. Seismic monitoring was performed with a 24-station borehole seismometer network. Using near–real-time information on induced-earthquake rates, locations, magnitudes, and evolution of seismic and hydraulic energy, pumping was either stopped or varied—in the latter case, between well-head pressures of 60 and 90 MPa and flow rates of 400 and 800 liters/min. This procedure avoided the nucleation of a project-stopping magnitude MW 2.0 induced earthquake, a limit set by local authorities. Our results suggest a possible physics-based approach to controlling stimulation-induced seismicity in geothermal projects.

The EPOS TCS-AH brings together a broad community interested in Anthropogenic Hazards (AH) related to induced seismicity. It is designed as a functional e-research infrastructure that provides access to a large set of relevant data and allows free experimentations in a virtual laboratory, promoting interdisciplinary collaborations between stakeholders (the scientific community, industrial partners and society). The platform provides datasets as Episodes, which comprehensively describe AH cases for infrastructures, people and/or environment. They are grouped in several categories of subsurface exploitations: CO2 sequestration, conventional hydrocarbon extraction, geothermal energy production, reservoir impoundment, unconventional hydrocarbon extraction, underground gas storage, underground mining, and wastewater injection. They gather datasets relevant for the considered hazards (e.g. seismic, air/water quality), industrial data (e.g. well path, injection rates, mining front advance, gas production, water level), and other geodata (e.g. geological section, velocity model, faults, shear wave velocity, bathymetric map). Two local data centers (eNodes: IG-PAS/Poland and CDGP-EOST/France) provide metadata and data to the TCS-AH platform in commonly used standards and formats (e.g. miniSEED, GeoTIFF, and .mat). A registration/authorization is mandatory to access some data covered by restriction imposed by data industry providers or shared data embargoed by running projects. The platform grants access to an application portfolio, designed for the AH area, and addressing: (1) basic services for data integration and handling; (2) services for physical models of stress/strain changes over time and space as driven by geo-resource production; (3) services for analyses of geophysical signals; (4) services to extract the relation between technological operations and observed induced seismic/deformation; (5) services to quantitative probabilistic assessments of anthropogenic seismic hazard - statistical properties of anthropogenic seismic series and their dependence on time-varying anthropogenesis; ground motion prediction equations; stationary and time-dependent probabilistic seismic hazard estimates, related to time-changeable technological factors inducing the seismic process; (6) simulator for multi-hazard/multi-risk assessment in exploration/exploitation of georesources (MERGER) - numerical estimate of the occurrence probability of chains of events or processes impacting the environment.

The SHEER database brings together a large amount of data of various types: interdisciplinary site data from seven independent episodes, research data and those for the project results dissemination process. This concerns mainly shale gas exploitation test sites, processing procedures, results of data interpretation and recommendations. The smart SHEER database harmonizes data from different fields (geophysical, geochemical, geological, technological, etc.), creates and provides access to an advanced database of case studies of environmental impact indicators associated with shale gas exploitation and exploration, which previously did not exist. A unique component of the SHEER database comes from the monitoring activity performed during the project in one active shale gas exploration and exploitation site at Wysin, Poland, which started from the pre-operational phase. The SHEER database is capable of the adoption of new data such as results of other Work Packages and has developed an over-arching structure for higher-level integration.

The community focused on seismic/aseismic deformation processes induced by human operation, organized within European Plate Observing System (EPOS) as WG10 “Infrastructure for Georesources” integrates distributed research infrastructures (RI) to facilitate and stimulate research on anthropogenic hazards especially those associated with the exploration and exploitation of geo-resources, within EPOS Thematic Core Service ANTHROPOGENIC HAZARDS (TCS AH). The innovative element is the uniqueness of the integrated RI which comprises two main deliverables : (1) Exceptional datasets, called “episodes”, which comprehensively describe a geophysical process induced or triggered by human technological activity, posing hazards for infrastructure, people and the environment; (2) Problem-oriented, bespoke services uniquely designed for analyzing correlations between technological activities, geophysical response and associated hazards, including e-research environment of IS-EPOS platform (is-epos.eu). These objectives will be achieved through the Science-Industry Synergy, ensuring bi-directional information exchange, including unique and previously unavailable data furnished by industrial partners and innovative solutions coming back to industry. The data and services are related to a wide spectrum of inducing technologies, with seismic/aseismic deformation and production history dataset. Impact of RI will be also reflected in a more multidisciplinary approach to education, and an opportunity for students to obtain skills and knowledge in the anthropogenic hazards field. The work is supported by project IS-EPOS: Digital Research Space of Induced Seismicity for EPOS Purposes (POIG.02.03.00-14-090/13-00), funded by the NCBiR in the OP Innovative Economy in the years 2013-2015.

On 27 December 2007, a 1.9 seismic event occurred within a dyke in the deep-level Mponeng Gold Mine, South Africa. From the seismological network of the mine and the one from the Japanese-German Underground Acoustic Emission Research in South Africa (JAGUARS) group, the hypocentral depth (3,509 m), focal mechanism and aftershock location were estimated. Since no mining activity took place in the days before the event, dynamic triggering due to blasting can be ruled out as the cause. To investigate the hypothesis that stress transfer, due to excavation of the gold reef, induced the event, we set up a small-scale high-resolution three-dimensional (3D) geomechanical numerical model. The model consisted of the four different rock units present in the mine: quartzite (footwall), hard lava (hanging wall), conglomerate (gold reef) and diorite (dykes). The numerical solution was computed using a finite-element method with a discretised mesh of approximately elements. The initial stress state of the model is in agreement with in situ data from a neighbouring mine, and the step-wise excavation was simulated by mass removal from the gold reef. The resulting 3D stress tensor and its changes due to mining were analysed based on the Coulomb failure stress changes on the fault plane of the event. The results show that the seismic event was induced regardless of how the Coulomb failure stress changes were calculated and of the uncertainties in the fault plane solution. We also used the model to assess the seismic hazard due to the excavation towards the dyke. The resulting curve of stress changes shows a significant increase in the last in front of the dyke, indicating that small changes in the mining progress towards the dyke have a substantial impact on the stress transfer.

The spatiotemporal, kinematic, and source characteristics of induced seismicity occurring at different fluid injection rates are investigated to determine the predominant physical mechanisms responsible for induced seismicity at the northwestern part of The Geysers geothermal field, California. We analyze a relocated hypocenter catalog from a seismicity cluster where significant variations of the stress tensor orientation were previously observed to correlate with injection rates. We find that these stress tensor orientation changes may be related to increased pore pressure and the corresponding changes in poroelastic stresses at reservoir depth. Seismic events during peak injections tend to occur at greater distances from the injection well, preferentially trending parallel to the maximum horizontal stress direction. In contrast, at lower injection rates the seismicity tends to align in a different direction which suggests the presence of a local fault. During peak injection intervals, the relative contribution of strike-slip faulting mechanisms increases. Furthermore, increases in fluid injection rates also coincide with a decrease in b values. Our observations suggest that regardless of the injection stage, most of the induced seismicity results from thermal fracturing of the reservoir rock. However, during peak injection intervals, the increase in pore pressure may likewise be responsible for the induced seismicity. By estimating the thermal and hydraulic diffusivities of the reservoir, we confirm that the characteristic diffusion length for pore pressure is much greater than the corresponding length scale for temperature and also more consistent with the spatial extent of seismicity observed during different injection rates.

The formation of fault damage due to slip under high normal stresses can rarely be monitored under in situ conditions. To advance our understanding of microfracture processes, we investigated stick-slip events on Westerly granite samples containing the following: (1) a planar saw cut fault and (2) a fault developed from a fresh fracture surface. We examined temporal changes of seismic moment tensors and b values of acoustic emission (AE) events. During experiment on the saw cut surface, small AEs exhibiting non-double-couple components were observed continuously and strong AEs displaying double-couple components were visible only when approaching the slip onsets. Sliding on naturally fractured surfaces showed, in addition to double-couple components, significant volumetric contributions, especially during the interslip periods and immediately after stick-slip events indicating substantial shear-enhanced compaction within a relatively broad damage zone. The obtained results shed light on how differences in fault structure control the kinematics of microseismicity during different periods of the seismic cycle.

The Thematic Core Service “Anthropogenic Hazards” (TCS AH) integrates data and provides various data services in a form of complete e-research infrastructure for advanced analysis and geophysical modelling of anthropogenic hazard due to georesources exploitation. TCS AH is based on the prototype built in the framework of the IS-EPOS project POIG.02.03.00-14-090/13-00 (https://tcs.ah-epos.eu/). The TCS AH is currently being further developed within EPOS Implementation phase (H2020-INFRADEV-1-2015-1, INFRADEV-3-2015). The TCS AH aims to have a measurable impact on innovative research and development by providing a comprehensive, wide-scale and high quality research infrastructure available to the scientific community, industrial partners and public. One of the main deliverable of TCS AH is the access to numerous induced seismicity datasets called “episodes”. The episode is defined as a comprehensive set of data describing the geophysical process induced or triggered by technological activity, which under certain circumstances can become hazardous for people, infrastructure and the environment. The episode is a time-correlated, standardized collection of geophysical, technological and other relevant geodata forming complete documentation of seismogenic process. In addition to the 6 episodes already implemented during previous phase of integration, and 3 episodes integrated within SHEER project, at least 18 new episodes related to conventional hydrocarbon extraction, reservoir treatment, underground mining and geothermal energy production are currently being integrated into the TCS AH. The heterogeneous multi-disciplinary data from different episodes are subjected to an extensive quality control (QC) procedure composed of five steps and involving the collaborative work of data providers, quality control team, IT team, that is being supervised by the quality control manager with the aid of Redmine platform. The first three steps of QC are performed at local data center and include the (1) transfer of episode data to the local data center, (2) data standardization and validation of formats, (3) metadata preparation according to TCS AH metadata scheme. The final two steps of QC are performed already at the level of TCS AH website and include (4) Contextual analysis of data quality followed by appearance of episode in TCS AH maintenance area, and finally the (5) Episode publication at TCS AH website.Project, funded under FP7-ENV.2012 6.4-2 (Grant 308417) and successfully implemented to Marmara Region during 2014-2016 indicated that focusing on the monitoring of the region and the integration of data from land, sea and space and the processing of this composed data based on sound earth-science research is an effective tool for mitigating damage from future earthquakes. This was achieved by monitoring the earthquake hazard through the ground-shaking and forecast maps, short- and long-term earthquake rate forecasting and time-dependent seismic hazard maps to make important risk-mitigation decisions regarding building design, insurance rates, land-use planning, and public-policy issues that need to balance safety and economic and social interests. MARSite has demonstrated the power of the use of different sensors in the assessment of the earthquake hazard. In addition to the more than 30 scientific publication within the MARsite Project framework, a multidisciplinary innovative borehole seismic observatory and a dilatometer have been installed within MARSite where its a data can be used for a range of seismic studies. Due to the encouraging results obtained from this experiment, it was determined that in the future likely smaller number of stations will be required reducing the cost of national seismic networks. The technical infrastructure of the continuous GPS stations of MAGNET network has been updated within MARSite. Tsunami hazard studies in MARSite in Marmara Sea showed that the tsunami hazard in the Marmara Region is primarily due to submarine landslides triggered by an earthquake and a conceptual Tsunami Early Warning System in the Marmara region strongly coupled with the strong ground motion and existing Earthquake Early Warning System was developed. The existing Earthquake Early Warning and Rapid Response system in the Marmara Region was improved and the installation and test of a pilot seismic landslide monitoring system was taken place in the Avcilar-Beylikdüzü Peninsula, a large landslide prone area located in westward part of Istanbul and facing the North Anatolian Fault Zone (NAFZ). An integrated approach based on multi-parameter seafloor observatories was implemented to continuously monitor the micro-seismicity along with the fluid expulsion activity within the submerged fault zone. During MARSite, strong integration and links had been established with major European initiatives focused on the collection of multidisciplinary data, their dissemination, interpretation and fusion to produce consistent theoretical and practical models, the implementation of good practices so as to provide the necessary information to end users, and the updating of seismic hazard and risk evaluations in the Marmara region. In this perspective, to continue the understanding of and improvement in the preparedness for geological disasters, the existing monitoring infrastructure of Marsite requires the continuation of a strong a European initiative. This presentation will provide a venue for information exchange towards the establishment of such an initiative.

Understanding the relation between injection‐induced seismic moment release and operational parameters is crucial for early identification of possible seismic hazards associated with fluid‐injection projects. We conducted laboratory fluid‐injection experiments on permeable sandstone samples containing a critically stressed fault at different fluid pressurization rates. The observed fluid‐induced fault deformation is dominantly aseismic. Fluid‐induced stick‐slip and fault creep reveal that total seismic moment release of acoustic emission (AE) events is related to total injected volume, independent of respective fault slip behavior. Seismic moment release rate of AE scales with measured fault slip velocity. For injection‐induced fault slip in a homogeneous pressurized region, released moment shows a linear scaling with injected volume for stable slip (steady slip and fault creep), while we find a cubic relation for dynamic slip. Our results highlight that monitoring evolution of seismic moment release with injected volume in some cases may assist in discriminating between stable slip and unstable runaway ruptures., Plain Language Summary: Anthropogenic earthquakes caused by fluid injection have been reported worldwide to occur in the frame of waste‐water disposal, CO2 sequestration, and stimulation of hydrocarbon or deep geothermal reservoirs. To study the dynamics of injection‐induced seismic energy release in a controlled environment, we performed laboratory fluid injection experiments on critically stressed high‐permeability sandstone samples with a prefabricated fault. We monitored acoustic emission occurring during injection‐induced fault sliding. We find that the total seismic deformation (expressed as total seismic moment) is related to total injected volume, independent of fault slip modes (i.e., dynamic slip, steady slip, and fault creep). Seismic moment release rate roughly scales with fault slip velocity. In our experiments, the fluid pressure front migrates faster than the rupture front by about 5 orders of magnitude, resulting in fault slip within a zone of homogeneous fluid overpressure. We find that cumulative seismic moment scales linearly with the injected volume for stable slip (steady slip and fault creep), while it follows a cubic relation for dynamic slip. Our experimental results suggest that the deviation of cumulative moment release with injected volume from a linear trend in practice might be a sign for potential seismic risk. This may be considered in modifying current injection strategies., Key Points: Injection‐induced fault deformation is dominantly aseismic. Total moment release depends on total injected volume, independent of fault slip behavior. Moment‐injected volume scaling is linear for stable slip but shows a cubic relation for dynamic slip.

Title: Source Parameters of Microearthquakes and their Uncertainty Author: Jan Michálek Department: Department of Geophysics Supervisor: Doc. RNDr. Tomáš Fischer, PhD., Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Charles University in Prague Abstract: The aim of this thesis is to analyze the spectral methods used for the determination of the earth- quake source parameters like the seismic moment M0 and the corner frequency fc and to apply these meth- ods to seismic data from the West Bohemian region. Considering some assumptions about the source the other important parameters like the source radius r or the stress drop in the source ∆σ can be evaluated. Determination of the parameters is performed in the spectral domain by comparing a simple Brune's source model (non-causal slip on a circular rupture; spectral slope ω−2) with the displacement of the P or S wave. The methods were applied to 56 selected earthquakes of the West Bohemian swarms from 2000 and 2008 by the absolute and relative approach in several modifications. The absolute method allows to determine not only the source parameters but also the quality factor Q (attenuation), which significantly affects the deter- mination of fc. Therefore, the absolute method was applied also as the joint inversion when Q is stabilized....