Co-seismic P-wave Velocity Changes of 2023 Türkiye Earthquake Doublet

On February 6, 2023, the Türkiye Earthquake Doublet, consisting of two major earthquakes with magnitudes of M_w7.8 and M_w7.5, respectively, occurred within 9 h and devastated the Kahramanmaraş province in southwest Turkey. The geodynamic background of this area is exceedingly complicated owing to the combined action of the Anatolian Plate and the neighboring Eurasian, African, and Arabian plates, which contain many faults, the most prominent of which is the East Anatolian Fault Zone (EAFZ). These two earthquakes occurred on the Pazarcık Segment (PAZ.S) of the EAFZ and the Çardak Fault (CAR. F). The investigation of co-seismic changes in the velocity structure of the subterranean medium inside the focus area is critical for our understanding of earthquake ruptures. We chose 51572 travel times before the earthquake doublet from January 1, 2014, to February 5, 2023, and 88371 travel times after the earthquakes from February 6 to March 5, 2023, and utilized time-lapse tomography to derive the co-seismic changes in P-wave velocity. The results demonstrated that the P-wave velocity decreased around the center zone, with considerable surface displacement from the two earthquakes caused by rock breakup and stress release. The P-wave velocity increased in two areas: east of the Pazarcik Earthquake, where the Bozova Fault is located, and west of the Elbistan Earthquake. We believe that these two locations are compression zones generated by the strike-slip surface displacement. Similarly, the decrease in velocity in the areas adjacent to the Malatya Fault (MAL.F) and between the Amanos Segment (AM.S) of the EAFZ and the Savur Fault (SA.F) shows that these two locations were exposed to tension as a result of the co-seismic horizontal displacement on the surface. This study showed that in addition to the area close to the epicenter, the large earthquake can affect the velocity structure of faults far away from the main shock.