Evidence for small-scale segmented fault rupture along the East Anatolian Fault during the Mw 7.8 2023 Kahramanmaraş earthquake

The rupture front of the first 25 s of the 2023 Mw 7.8 Kahramanmaraş earthquake is tracked using the P-wave polarization vector vs time as measured by the dense three-component accelerometer network surrounding the slipping fault. We find a coherent increase of the spatially variable rupture velocity along portions of the earthquake fault zone where high coseismic slip has been previously mapped by kinematic source imaging studies. This is clearly detected in a domain of the Pazarcık segment of the East Anatolian Fault located at about 40 km NE of the mainshock epicenter where the rupture velocity rises to super-shear values. This domain spatially matches the part of the Pazarcık segment where most micro-earthquakes nucleate in the inter-seismic phase and edges at north a nearly aseismic domain. We postulate the existence of velocity-weakening subsegment on the Pazarcık fault sandwiched between velocity strengthening domains and/or mechanic barriers to the fault slipping.