Coseismic deformation of the 2022 Luding <italic>M</italic><sub>S</sub>6.8 earthquake and seismic potential along adjacent major faults

Abstract

<p indent="0mm">The 2022 Luding (Sichuan) <italic>M</italic>6.8 earthquake occurred on the Moxi segment of the Xianshuihe fault, one of the most seismically active faults in mainland China. Since 1900, six moderate to strong earthquakes (&gt; <italic>M</italic>6.5) have ruptured different sections of the Xianshuihe fault. This Moxi segment has a complex tectonic setting as it forms an intersection zone of the Anninghe, Daliangshan, Xiaojin, and Longmenshan faults. In this study, we investigated the distribution of coseismic deformation of the 2022 Luding earthquake in order to improve understanding of the seismogenic fault and gain insight into the kinematic behaviors of regional faults and seismogeneity of future strong earthquakes. We collected continuous global positioning system (GPS) and strong motion data within 200 and <sc>50 km</sc> from the epicenter, respectively, and performed high-precision processing to extract the coseismic deformation field of this earthquake. We also collected Sentinel-1 and Advanced Land Observing Satellite-2 (ALOS-2) ScanSAR model descending data covering the epicenter area, and processed these data using differential interferometric synthetic aperture radar (D-InSAR) technology. The GPS measurements confirm that deformation from this earthquake occurred as far as <sc>200 km</sc> from the fault. This coseismic deformation was distributed in four quadrants, indicating that the focal mechanism of the Luding earthquake was left-lateral strike-slip. A strong motion station <sc>16 km</sc> from the epicenter recorded a significant displacement waveform; peak ground displacement was <sc>14 cm</sc> and the permanent coseismic displacement was <sc>12 cm.</sc> InSAR deformation maps show significant coseismic deformation in a 30 km×<sc>30 km</sc> area along the fault. The maximum line-of-sight displacement reached <sc>15 cm</sc> to the west of the fault. In addition, significant local deformation (&gt; <sc>15 cm)</sc> was observed near the Wajiao township. Field investigations suggest that surface ruptures developed along the fault segment between Ertaizi and Aiguocun. However, it is difficult to identify rupture information from the InSAR maps owing to a loss of coherence in the near-field of the seismogenic fault. Detailed field investigations are needed to determine if coseismic slip reached the surface. Finally, we inverted interseismic coupling along the northeastern boundary faults of the Sichuan–Yunnan block, and quantitatively calculated the seismic moment budget on these faults. Based on the historical earthquake distribution of the past <sc>300 years</sc> and present-day fault locking conditions along the Xianshuihe fault, the Luding earthquake accommodated clockwise vertical-axis rotation of the expanding Qinghai-Tibetan Plateau relative to the South China Block. The earthquake fully released the strain accumulated on the Moxi segment since the 1786 Moxi <italic>M</italic>7³/₄ earthquake; as such, it is unlikely that large earthquakes will occur on the Moxi segment in the near future. However, we also performed a comprehensive investigation of seismic hazard along the Xianshuihe-Xiaojiang fault system based on the mapped seismic gap, asperity distribution, seismic moment deficit, and Coulomb failure stress caused by surrounding earthquakes. We found that the seismic moment accumulated on the Anninghe, Zemuhe, Daliangshan, and southern Longmenshan faults can be balanced by <italic>M</italic>_w7.0–7.7 earthquake. The Luding earthquake caused significant Coulomb stress loading (&gt; <sc>0.01 MPa)</sc> on the Daliangshan, Anninghe, and southern Longmenshan faults, bringing those faults closer to failure. In particular, Coulomb stress loading at the northern end of the Anninghe fault exceeded the conventional triggering threshold <sc>(0.1 MPa)</sc> for earthquakes; therefore, the risk of future strong earthquakes on the Anninghe fault deserves special attention.