2022 Mw 6.6 Luding Earthquake Sequence: A Complex Fault System From InSAR Displacement Observations

The 2022 Mw 6.6 Luding earthquake sequence provides an opportunity to explore the geometry, seismic hazard, and regional tectonics of the Moxi fault, the southeastern segment of the Xianshuihe fault. We applied Interferometric Synthetic Aperture Radar (InSAR) techniques to Advanced Land Observing Satellite‐2 (ALOS‐2) and Sentinel‐1 multi‐source data sets, and reconstructed the coseismic displacement field and corresponding slip distribution of the mainshock. Using a single InSAR pair, we retrieved early postseismic displacements to the west of the Moxi fault. Adaptive cluster‐based stratification correction was used to correct the atmospheric phase and accurately retrieve coseismic and postseismic displacements. Okada model inversion confirmed shallow (<6 km depth) aseismic slip on a normal fault near the western Moxi fault. This slip likely commenced immediately after the mainshock and decelerated over time. Moreover, we observed slight eastward extension of the aseismic slip zone during the postseismic period. The spatio‐temporal distributions of slip and aftershocks coincide with a large stress increase zone (0.15–0.2 MPa) induced by the mainshock. Models of regional gravity potential energy and the regional strain field indicate the possibility of pre‐existing normal faults with various strike directions. Our results indicate two potential mechanisms to explain the observed postseismic deformation: (a) reactivation of these normal faults (both aseismic slip and sequential normal earthquakes) in response to mainshock‐induced tensional stress; and/or (b) ground subsidence caused by the mainshock‐triggered pore pressure reduction. Based on forward 1D pore elastic modeling, both mechanisms may have contributed to the observed postseismic surface deformation.