Kandilli Observatory and Earthquake Research Institute

We investigated the geometry and the kinematics of the Sındırgı fault, which was activated during the two M6+ earthquakes (10.08.2025 and 27.10.2025) and their aftershocks. We analyzed all available seismographs from KOERI (Kandilli Observatory and Earthquake Research Institute) and AFAD (Disaster and Emergency Management Authority) to identify fault geometry, earthquake locations, and focal mechanisms. We analyzed P-wave initial polarities and arrival times of a total of 43 M4+ earthquakes including two mainshocks (waveforms from KOERI and AFAD). Fault plane solutions as well as the accurate hypocenter locations indicate that the majority of the mainshocks and the aftershocks activated a south dipping fault. The results indicate an average strike of 110 ± 5.6°, a dip of 61.6 ± 4.4°, and rake a rake -124.6 ± 2.3°. Additionally, we investigated inter-seismic slip rates using 2D dislocation model analyzing the GNSS velocity field. We transformed the most recent velocity field into Anatolian-fixed reference frame. We decomposed GNSS velocities into fault-parallel and fault-perpendicular components and applied 2D arctan curve fitting to simultaneously determine the slip rates and the fault locking depths. Bootstrap error analysis was performed (1σ) to assess error bounds. The lateral motion is nearly negligibly small; however, fault-perpendicular velocities indicate the extension along the Sındırgı fault at 2.34 ± 0.69 mm/y slip rate. Inter-seismic slip rates suggest a rake of -95.2°, a nearly pure normal fault, which is consistent with average mainshock-aftershock rakes. In this context, GNSS-derived interseismic slip rates are capable of forecasting the extensional kinematics of the Sındırgı fault that generated two predominantly normal-faulting M 6+ earthquakes in 2025.

Active continental extension in the western Anatolia-Aegean (since approximately 25 Ma) drives exhumation of several metamorphic core complexes, low angle normal (detachment) faulting, and NE-SW and NW-SE trending strike-slip tectonics. However, the causative relationships among these processes and structures remain poorly understood. Here, we use 3-D thermomechanical numerical models to investigate how strain localization evolves in a stretching continent with plate rotations along a vertical axis. Namely, we test the obliquity of extension between 15° and 60°, the extension velocity of 1–2 cm/yr applied at the plate boundary, an initial crustal thickness of 50 km and a lithospheric thickness of 130 km, as well as the temperature gradient. To characterize the geometry of the fault systems, we calculate the Regime Stress Ratio (RSR) from the stress tensor and evaluate it in regions of high strain rate. We reconcile our model results with up-to-date structural features, including velocity fields from GPS, InSAR data, seismic receiver functions, and regional earthquake datasets from various sources. Preliminary results show that obliquity angle and initial layer thicknesses are first order parameters controlling strain localization, while simultaneously generating significant conjugate strike-slip tectonics. This is in accord with the formation of NE-SW and an array of NW-SE trending faults and clustering of earthquakes (relocated between 2010–2025) along the boundaries of the Gediz, Büyük Menderes and Simav grabens. These findings provide a modeling framework that links fault geometries, metamorphic core complex exhumation, and strike-slip deformation to the extensional tectonics and deeper lithospheric structure beneath the region.

Abstract A series of earthquakes along the East Anatolian Fault Zone (EAFZ) started with the January 24, 2020, Sivrice (Elazığ) Earthquake (M W 6.8) and culminated in the the catastrophic Kahramanmaraş Earthquakes (M W 7.8 and M W 7.6) on February 6, 2023. This study explores how the 2020 Sivrice event influenced the 2023 Kahramanmaraş earthquakes using field surveys and seismotectonic analyses. The 2020 earthquake, occurring in the northeastern part of Pütürge Segment, was followed by field surveys and Differential interferometry (DInSAR) analysis to determine fault geometry and slip distribution. Seismological studies, including moment tensor solutions, stress tensor analysis, and Coulomb stress changes, provided insights into the fault dynamics. Surface deformations were observed in a 50 km section of the Pütürge segment, showing R, R’, T, P, and Y fractures typical of a left-lateral deformation zone. The moment tensor analysis revealed a left-lateral strike-slip fault trending N65°E, with a minor normal component. The timing and location of the earthquakes, suggest that the rupture progresses bilaterally. The analysis of Coulomb stress changes showed that the 2020 event transferred stress to the Arıkonak sub-segment, the Yarpuzlu restraining double-bend, the Erkenek Segment of the EAFZ, as well as the Gerger and Narince Segments of the Southeastern Anatolian Thrust Zone. These areas were further stressed by the 2020 earthquake, setting the stage for the February 2023 Kahramanmaraş events. Thus, the 2020 Sivrice earthquake served as a trigger for the catastrophic 2023 earthquakes. The Arıkonak sub-segment, Gerger, and Narince segments are still potential sources of earthquake hazard.

Abstract Solar superflares of S‐class (>X10 in soft X‐rays) pose extreme space weather hazards, yet their prediction remains a fundamental challenge owing to their rapid and transient natures and the limitations of conventional event‐based forecasts. We introduce for the first time, a probabilistic spatiotemporal framework designed to identify extended epochs and heliographic zones with heightened superflare likelihood, rather than predicting individual events. Our methodology analyzes nearly five decades of Geostationary Operational Environmental Satellites SXR observations (1975–2025) and introduces two novel components: (a) a cross‐Laplacian diagnostic, derived from the butterfly diagrams of sunspot area and SXR flare density, which identifies photosphere‐corona coupling and pinpoints magnetic energy accumulation sites as preferential zones for S‐flare occurrence; and (b) a temporal model based on the coupled phase states of 1.7‐year and 7‐year oscillations, extracted via wavelet analysis and projected forward using a Bayesian Least‐Squares Support Vector Machine method. Integrating these spatial and temporal diagnostics yields a unified forecast, we identify 2025.7–2026.6 and 2027.2–2027.9 years, as the primary high‐probability windows for S‐class flare activity during Solar Cycle 25, corresponding preferentially to latitudinal bands in the southern (S–S) and northern (N–N) hemispheres, respectively. Subsequent windows are projected for Cycle 26. This physics‐informed, probabilistic approach provides a robust strategy for anticipating periods of extreme solar activity by characterizing the inherent patterns of magnetic energy storage and release in the solar atmosphere.

The densely populated areas in the Eastern Mediterranean are highly vulnerable to a variety of geohazards, including earthquakes, tsunamis, volcanoes and landslides. The Cyclades archipelago region near Santorini in the Aegean Sea lies within a tectonically active belt capable of generating volcanic activity, major destructive earthquakes and subsequent landslides and/or tsunamis. Understanding the properties of plate boundaries, slabs, active faults and the stress field is crucial for identifying the geodynamic factors driving plate deformation and associated geohazards. A dense seismic network is crucial for precisely locating earthquakes and understanding the active tectonics of the area. In recent years, dense seismic networks such as AdriaArray, have been conducted to provide high quality data for imaging crustal and upper mantle structure, as well as analysing seismic activity in the Mediterranean region. This study focuses on the computation of a 1D velocity model in order to improve the earthquake parameters in the region. Taking advantage of recent deployments, dense station coverage, and a comprehensive earthquake catalogue from recent seismic activity in the Cyclades archipelago, Aegean Sea, a new 1D crustal velocity model was developed and compared with existing models in the region. The presented results emphasize the influence of the crustal velocity model on earthquake parameters and moment tensor solutions, with strong potential to enhance forthcoming investigations into source mechanisms, fault kinematics, and seismic velocity structures in the Aegean Sea.

Abstract A new daily composite of the solar flare index (SFI) and the hemispherically‐resolved versions (hSFI) are presented for 1937 to 2024. The data set confirms that the northern hemisphere (NH) dominated solar flare activity during Solar Cycles 17 to 21, but that the southern hemisphere has dominated from Solar Cycle 22 to present. That said, the highest SFI value occurred in the NH during the recent superstorm of May 2024. In sunspot activity, the “Gnevyshev‐Ohl rule” shows that the sum of sunspot numbers during even‐numbered cycles is related to those of adjacent odd‐numbered cycles. A similar rule appears to apply to SFI. The “Gnevyshev gap” phenomenon where solar maximum activity sometimes has two peaks separated by up to 1–2 years of a gap is confirmed for SFI. Although our data set represents the longest continuous daily data set for solar flare activity to‐date, it is known that stronger solar flare events occurred before 1937. Therefore, a brief discussion of earlier solar flare events in the historical record is also provided for context. The statistics of the SFI and hSFI series are compared to other solar and geomagnetic activity indices, including the May and October 2024 solar storms. Statistical analysis of past geomagnetic storms confirms they are more frequent during active cycles and less frequent during solar minima. Strong geomagnetic storms are also more likely to occur during the positive phase of a 1.7 year's quasi‐biennial oscillation in solar activity. The likelihood of low‐magnetic latitude aurorae seems to have a 30 year periodicity component.

Abstract Rupture speed is a crucial parameter of earthquake dynamics and influencing associated seismic hazards. Accurately resolving the rupture evolution of large earthquakes is essential for identifying factors governing earthquake physics. In this study, we investigate the kinematic rupture processes of the 2023 Mw7.8 and Mw7.7 eastern Turkey earthquake doublet. We integrate various complementary data sets and methods, including 3D surface deformation, teleseismic back‐projection, near‐fault strong motion waveform analysis, and finite fault inversions, to resolve the rupture details. Our results reveal that the Mw7.8 earthquake predominantly involves an asymmetric bilateral rupture on the main fault, with part of the northeastward rupture reaching super‐shear speed (∼5.2 km/s), while the southwestward rupture propagates primarily at the generalized Rayleigh speed (∼3.4 km/s), a characteristic of an inhomogeneous fault zone separating two dissimilar materials. This directional dependence on rupture speed may be attributed to a material contrast between the softer Anatolian plate and the stiffer Arabian plate, as supported by the fault zone head wave observations and tomography models. In contrast, the Mw7.7 event features a bilateral super‐shear rupture, likely due to its occurrence on intraplate faults without substantial material contrast across the fault. This study underscores the importance of incorporating detailed fault zone structures and high‐quality near‐fault observations into earthquake physics and seismic hazard analysis.

SUMMARY The ∼300 km-long rupture of the 2023 February 6 Kahramanmaraş earthquake began in the Narlı section of the Karasu trough, a pull-apart basin sandwiched and sheared between the two major strike-slip faults of the region, the East Anatolian Fault (EAF) on the west and the Dead Sea Fault (DSF) on the east. Rupture started where the northern segment of the DSF enters the Narlı Basin with Mw7.0 sub-event and propagated across the basin before making its junction with the EAF. In the seven months preceding the earthquake this basin was the seat of anomalous seismic activity. This activity occurred in bursts interweaved with periods of quiescence. It started near-concomitantly in two clusters located on the opposite edges of the pull-apart basin ∼20 km apart. The organization of this seismicity into families of numerous repeating earthquakes suggests an aseismic process linked to fault healing and rapid reloading in a critically stressed zone. By December 2022, two months before the earthquake, activity had migrated to a cluster located along the path that rupture was to follow during the initial stage of the earthquake. These observations show that the pull-apart basin where rupture started was progressively deforming in a succession of bursts before the earthquake. This regional-scale deformation is closely linked with the transitional nature of geodynamics and kinematics influenced by large-scale fault interactions in the surrounding area. The location of the epicentre near the northern termination of the rupture of the 1822 M7.4 earthquake suggests that the ∼45 km long Narlı sub-rupture which constituted the first stage of this giant earthquake was closing a long-present seismic gap between the DSF and the EAF.

Türkiye is known as one of the most seismically active regions in the world due to its rapidly deforming tectonic properties that has been developed by the northward movement of the African and Arabian plates relative to the Eurasian plate. These plate movements caused the Anatolian plate to be compressed in the east and move westward, resulting in the formation of the most important tectonic structures in the region, the North Anatolian Fault Zone (NAFZ) with ∼1500 km length and right-lateral strike-slip motion in the east-west direction, and the East Anatolian Fault Zone (EAFZ) with ∼700 km length and left-lateral strike-slip motion in the northeast direction. Historical records show that seismic energy release along the NAFZ migrated westward with large earthquakes, i.e., the 1939 Erzincan earthquake (Mw7.9), 1942 Erbaa-Niksar earthquake (Mw7.0), 1999 İzmit earthquake (Mw7.4), and 1999 Düzce earthquake (Mw7.2). However, two significant seismic gaps exist throughout the NAFZ; Marmara and Yedisu. We, in particular, examined the Yedisu Seismic Gap (YSG) in this study, by investigating the interrelationships between seismicity, Coulomb stress changes, seismotectonic b-values, and surface deformation with the aim of understanding the characteristics and seismic hazard potential in and around the YSG. More specifically, we analyzed the seismic activity of the eastern NAFZ extending from the Erzincan basin to the Karlıova Triple Junction (KTJ) using earthquake catalogs from 1900 to 2024, which include both Mw≥1 earthquakes and Mw≥4 earthquakes. 3D Coulomb stress change behavior was compared with the background seismicity pattern in the region. We further performed a joint interpretation of lateral variation of statistical b-values, seismic P- and S-wave speeds, and InSAR-based surface deformation in order to understand possible regions of asperities or high pore-pressure where the accumulated stress often released due to the decreasing normal stress on the fault. Our preliminary results indicate that the stress has been transferred to the YSG following the 14 June 2020 Mw5.7 Karlıova earthquake. The results of our multi-data analysis will provide invaluable insight into the current seismic hazard potential of the YSG, which will be essential for future urban planning in this region.