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The M w 7.8 earthquake in Turkey on 6 February 2023 was extraordinary for various reasons. It originated in depth of only 10 km, ruptured along a fault plane around 300 km long and the surface was covered by an extensive network of high-quality seismic instruments. The strong motions resulted in a vast number of tragic casualties and huge material losses in Turkey and Syria. However, abundant and proximate seismic observations of this event and numerous aftershocks give an opportunity to deepen the understanding of earthquake processes. In this study, we carried out an assessment of coseismic changes of seismic velocity using passive image interferometry. We used data from one strong-motion and twenty-four broad-band sensors. We observed coseismic drops of seismic velocity, which reached up to −1.79 per cent at a location directly at the ruptured East Anatolian Fault Zone. Along the M w 7.8 earthquake fault, we observe frequency dependence of the velocity changes. At frequencies above 0.5 Hz, the velocity drops seem to be higher at locations close to the ruptured faults than in the more distant areas. [ABSTRACT FROM AUTHOR]

The Global Positioning System (GPS), although it has existed for only 30 years, is an important source for active tectonics, resulting in estimates of plate motions very close to geologic estimates over millions of years. GPS is also used for elastic block models to calculate slip rates for a better understanding of Earth's active crustal deformation. GPS-derived velocity fields may be used as the basis for clustering analysis to create a preliminary definition of block geometry. In this study, we used published horizontal velocity fields to evaluate the effects of data dependences on determining the optimum number of clusters with algorithms. For this purpose, we used different variations of velocity fields in Turkey and tested four different algorithms that are Davies–Bouldin index, the elbow method, GAP statistics algorithm and the silhouette method. We also clustered velocity components with the k -means technique and compared the results with previous studies. [ABSTRACT FROM AUTHOR]

SUMMARY As a part of the DEad Sea Integrated REsearch (DESIRE) project a near-vertical incidence reflection (NVR) experiment with a profile length of 122 km was completed in spring 2006. The profile crossed the southern Dead Sea basin (DSB), a pull-apart basin due to the strike-slip motion along the Dead Sea Transform (DST). The DST with a total displacement of 107 km since about 18 Ma is part of a left-lateral fault system which connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a distance of about 1100 km. The seismic experiment comprises 972 source locations and 1045 receiver locations. Each source was recorded by ∼180 active receivers and a field data set with 175 000 traces was created. From this data set, 124 444 P-wave first-break traveltimes have been picked. With these traveltimes a tomographic inversion was carried out, resulting in a 2-D P-wave velocity model with a rms error of 20.9 ms. This model is dominated by a low-velocity region associated with the DSB. Within the DSB, the model shows clearly the position of the Lisan salt diapir, identified by a high-velocity zone. A further feature is an unexpected laterally low-velocity zone with P-velocities of 3 km s-1 embedded in regions with 4 km s-1 in the shallow part on the west side of the DSB. Another observation is an anticlinal structure west of the DSB interpretated to the related Syrian arc fold belt. [ABSTRACT FROM AUTHOR]

Inversion of Pn traveltime residuals from a 39-station broad-band array provides a high-resolution image of the velocity structure in the uppermost mantle beneath central Turkey. Individually picked Pn phase arrivals from events recorded by the North Anatolian Fault Passive Seismic Experiment and the Kandilli Observatory were combined with additional events associated with the Eastern Turkey Seismic Experiment. Tomography results show no change in Pn velocity across the North Anatolian Fault, although longitudinal variations are evident. A region of very low Pn velocities (<7.8 km s−1) is imaged east of the Central Anatolian Fault Zone (CAFZ), with a transition to faster velocities (>8.1 km s−1) west of the fault. The sharp transition along the CAFZ, which follows the palaeotectonic Inner-Tauride Suture, may represent the location of the edge of the slab window, created when the oceanic slab broke off along the Bitlis-Zagros Suture around 11 Ma, as the Arabian plate collided with the Eurasian plate. [ABSTRACT FROM AUTHOR]