Evidence of Early Supershear Transition in the Feb 6th 2023 Mw 7.8 Kahramanmaraş Turkey Earthquake From Near-Field Records

Abstract

The Mw7.8 Kahramanmaraş Earthquake was larger and more destructive than what had been expected for the tectonic setting in Southeastern Turkey. By using near-field records we provide evidence for early supershear transition on the splay fault that hosted the nucleation and early propagation of the first rupture that eventually transitioned into the East Anatolian fault. We also find, for the first time ever, field observational evidence showing the mechanism of sub-Rayleigh to supershear transition. We estimate the instantaneous supershear rupture propagation speed to be ∼ 1.55Cs and the sub-Rayleigh to supershear transition length to be around ∼ 19.45 km, very close to the location of one of the stations, closest to the epicenter. This early supershear transition might have facilitated the continued propagation and triggering of slip on the nearby East Anatolian Fault leading to amplification of the hazard. The complex dynamics of the Kahramanmaras ̧ earthquake warrants further studies.