The 2023 Mw7.7 Pazarcik earthquake caused a reversal in vertical motion along the SW branch of the East Anatolian fault

Abstract

While the structural deformation at the Arabia-Anatolia-Africa junction is critical for understanding eastern Mediterranean tectonics, it remains debatable (extensional or compressional). Field survey of the 2023 Mw7.7 Pazarcik earthquake surface rupture along the Amanos Range, and microstructure and composition analyses of related fault rock were performed to investigate this issue. The surface rupture shows transtensional branches, with the main and secondary strands displaying sinistral (normal) offsets of 2.0–4.0 (0.4–0.9) and 1.0 (0.2) m. Slip plane of the secondary fault is marked by a ∼20 cm wide extensional fracture dividing fault breccia from gouge. Meanwhile, the gouge (26 % calcite, 38% serpentine and 36% smectite) is also dominated by tension cracks microscopically. In contrast to the widespread extensional deformation, geological evidence imply that this fault had experienced reverse slip in the Quaternary, as shown by thrusting of serpentine onto alluvium and the consistency of R foliations with reverse shear. We interpret it as the SW continuation of the East Anatolia fault (EAF) that was formerly characterized by transpressional deformation, and reactivated transtensionally due to the change of fault strike during this earthquake. In the broader Mediterranean tectonics framework, the Amanos segment might be interpreted as a recently formed component linking the Karasu fault to the EAF.