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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