Slow and progressive deformation of the Narlı pull-apart basin prior to the 2023 <i>M</i>w7.8 Kahramanmaraş, Turkey earthquake

SUMMARY The ∼300 km-long rupture of the 2023 February 6 Kahramanmaraş earthquake began in the Narlı section of the Karasu trough, a pull-apart basin sandwiched and sheared between the two major strike-slip faults of the region, the East Anatolian Fault (EAF) on the west and the Dead Sea Fault (DSF) on the east. Rupture started where the northern segment of the DSF enters the Narlı Basin with Mw7.0 sub-event and propagated across the basin before making its junction with the EAF. In the seven months preceding the earthquake this basin was the seat of anomalous seismic activity. This activity occurred in bursts interweaved with periods of quiescence. It started near-concomitantly in two clusters located on the opposite edges of the pull-apart basin ∼20 km apart. The organization of this seismicity into families of numerous repeating earthquakes suggests an aseismic process linked to fault healing and rapid reloading in a critically stressed zone. By December 2022, two months before the earthquake, activity had migrated to a cluster located along the path that rupture was to follow during the initial stage of the earthquake. These observations show that the pull-apart basin where rupture started was progressively deforming in a succession of bursts before the earthquake. This regional-scale deformation is closely linked with the transitional nature of geodynamics and kinematics influenced by large-scale fault interactions in the surrounding area. The location of the epicentre near the northern termination of the rupture of the 1822 M7.4 earthquake suggests that the ∼45 km long Narlı sub-rupture which constituted the first stage of this giant earthquake was closing a long-present seismic gap between the DSF and the EAF.