The 2023 Mw7.8 Kahramanmaraş, Turkey Earthquake: A Multi-segment Rupture in A Millennium Supercycle

An Mw 7.8 earthquake occurred on the East Anatolian Fault (EAF) and the secondary Narlı Fault (NF) on Feb 6, 2023, closely followed by an Mw 7.5 event on the Sürgü Fault 9 hours later. We analyze the distant and local seismic data, high-rate GPS recordings, and radar satellite images by Slowness Enhanced Back-Projection and joint Finite Fault Inversion for the Mw 7.8 event to resolve its rupture process. The rupture first initiates and propagates on the NF. After reaching the junction with the EAF, it propagates bilaterally on the EAF, extending 120 km to the northeast at 3.05 km/s and 200 km to the southwest at 3.11 km/s. The southwest speed is further verified by local seismic recordings and the absence of Mach surface wave characteristics. Compared with the EAF, the NF features denser seismic activity in recent decades, suggesting that it was more favorable for rupture nucleation. The EAF segments where the largest coseismic slip occurred have been relatively quiescent since the late 1800s. But the coseismic slip is much larger than the slip deficit accumulated during this period, which could be attributed to an ~900-year supercycle. The EAF geometry is similar to other active fault systems, such as the San Andreas Fault (SAF) and San Jacinto Fault (SJF). Considering high slip rates, resemblant supercycle mode, and the lack of large earthquakes on the southern SAF and SJF since 1857, an M8 earthquake could potentially occur there if most moment accumulation is released at once.