Source Mechanisms and stress fields of the 6 February 2023 Pazarcık Mw7.7 and Elbistan Mw7.6 earthquake sequences in SE Türkiye

Abstract

We investigate aftershock centroid moment tensor solutions along the Pazarcık Mw7.7 and Elbistan Mw7.6 February 6, 2023 rupture zones during the time period February 2, 2023 – November 25, 2024.  Six spatial clusters of aftershock activity are analyzed specifically the Çardak Cluster (ÇC), Doğanşehir  Cluster (DC), Sürgü Cluster (SC), Erkenek Cluster (EC), Pazarcık Cluster (PC) and Amanos Cluster (AC)  named according to the segmentation models of the Pazarcık‑Elbistan rupture zone. Based on an  aftershock hypocenter catalogue restricted to events with horizontal and vertical errors <2 km, we  determine fault plane solutions for 178 events. Centroid moment tensor solutions with moment magnitudes between 3.7 and 7.7 are computed by applying a waveform inversion method on data from the Kandilli Observatory and Earthquake Research Institute (KOERI) and the Disaster and Emergency Management Presidency Earthquake Department (AFAD) broadband seismic networks. The high number of moment tensors at the Pazarcık‑Elbistan rupture zone could be determined only thanks to the local seismic network and allows us to resolve the local deformation pattern with unprecedented precision. Moment tensors along the Çardak, Doğanşehir, Sürgü, Erkenek and Pazarcık Clusters allow us to identify dominantly sinistral strike‑slip mechanisms with normal faulting components on NE‑SW trending fault planes. Moreover, moment tensors in the Amanos Cluster predominantly exhibit NE‑SW extensional normal faulting but also a substantial component of strike‑slip faulting. North and southeast of the Çardak Cluster we observe a high variance in stress field orientation correlated with lower Coulomb stress values. While the Pazarcık Cluster reflects a predominant sinistral strike‑slip regime with normal faulting components, the Çardak Cluster further to the north that also hosted the forthcoming Elbistan Mw7.6 mainshock 9 hours after the Pazarcık Mw7.7 earthquake represents pure left‑lateral strike‑slip faulting. Stress tensor inversions of the aftershock focal mechanisms show rotations of the local stresses following the Pazarcık and Elbistan mainshocks. In the Pazarcık‑Elbistan mainshock area, the maximum horizontal compressive stress axis is horizontally rotated clockwise by ~65° with respect to the coseismic and long‑term regional stress field. Towards the northern end of the rupture where the Elbistan mainshock area is located, stress orientations are rotated clockwise steadily. We conclude that the Pazarcık earthquake caused significant stress partitioning along the rupture. The direction of stress rotation is related to the orientation of the individual fault segments like the Çardak Fault along the EAFZ.