Direct Rupture Speed Estimation from "Rupture Phase" of the 2023 Turkey Mw 7.8 Earthquake

Rupture speed is a fundamental dynamic characteristic of earthquakes, which can be inferred by multiple approaches such as the back projection (BP) and kinematic fault slip inversion with near-field or far-field data as constraints. Here we propose a rapid estimate for rupture speed directly from the strong motion records along the southern segment of the Mw 7.8 Turkey earthquake on 6 Jan 2023. We collect data on 12 strong motion stations that are located within 3 km from the major fault trace. Due to the short distances to the fault, the ground motions on these stations can approximate a very local rupture phase, with the peak amplitudes of fault-parallel velocities corresponding to the rupture front passage. We pick peak velocities on three components and obtain an apparent propagation speed of ~ 3 km/s. To validate the correlation between the rupture speed and the apparent rupture-phase speed, we conduct 3-D dynamic rupture simulations for this Mw 7.8 event and compare the synthetic rupture front with the rupture phase. We find that the rupture speed is slightly higher than the rupture-phase speed with a difference of 5% - 10%. Based on our modeling results, we infer the actual rupture speed of ~3.2 km/s along the south segment in the Mw 7.8 Turkey earthquake. Different from those waveform-fitting methods that require certain assumptions on the earthquake source, such as the relation between the rupture front and the radiation process or the slip rate function, our approach provide a fast and robust rupture speed estimation that can be done in real time.