2022 Mw 6.6 Luding, China, Earthquake: A Strong Continental Event Illuminating the Moxi Seismic Gap

Abstract

Abstract On 5 September 2022, an Mw 6.6 strike-slip earthquake occurred in Luding, Sichuan, China. It illuminates the seismic gap on the southern end of Xianshuihe fault zone, that is Moxi segment, and is the most damaging earthquake in Chinese Mainland since 2014. In this article, we use multiple seismological methods to analyze the basic characteristics of the Luding earthquake, including its source parameters, rupture process, aftershock distribution, and further discuss its implications on preseismic fault behavior and impact on short-term seismic hazard. Using near-field stations, we first revisit the source parameters of the mainshock and obtain a much shallower hypocentral depth (∼9.3 km) than previously reported. Next, we jointly inverse the teleseismic P-wave data and near-field strong-motion data to constrain the mainshock rupture process. The coseismic slip consists of two subevents that spans for ∼20 km and shows an overall unilateral rupture to the south-southeast direction. The earthquake has 90% of the seismic moment released in its first 10 s. Third, we relocate the first 34 days of aftershocks with both manual phase picks and cross correlation, and finally obtain 5269 well-located events. The aftershocks reveal a near-vertical Xianshuihe fault and two sets of unmapped faults off the major Xianshuihe fault: one set of strike-slip faults on the north-northwest of rupture and the other one on the west of mainshock that generates the most intense seismicity with prevalent normal faulting. By examining the aftershock evolution and Coulomb stress change, we find that postseismic processes evolve both on and off the major fault, and the western off-fault system has highly variable fault orientations. Finally, we calculate the Coulomb stress change by the Luding earthquake on surrounding faults. Results show that the north Anninghe fault is significantly loaded by the Luding earthquake (>0.1 MPa), which poses high seismic hazard in the short term.