Small-scale segmented fault rupture along the East Anatolian fault during the 2023 Kahramanmaraş earthquake

Rupture velocity affects the shaking damage potential of an earthquake, but it is hard to estimate. Here we track the rupture front of the first 25 s of the 2023 Kahramanmaraş earthquake 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 rupture velocity along portions of the fault zone where high coseismic slip has been previously mapped. This is detected in a domain of the Pazarcık segment of the East Anatolian fault at 40 km NE of the mainshock epicenter where the rupture becomes super-shear. 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 a velocity-weakening subsegment on the Pazarcık fault sandwiched between velocity-strengthening domains and/or mechanic barriers to the fault slipping. The locations of the highest rupture velocity during the 2023 Kahramanmaras earthquake coincided with the regions of greatest coseismic slip and inter-seismic microearthquake production, according to accelerometer data from the first 25 s after nucleation.