Seismicity characteristics and interseismic locking of the Anninghe Fault, Southwest China: Insights from long-term dense seismic array observations

Abstract Long-term earthquake catalogs can offer valuable constraints for investigating fault geometry and locking patterns at depth, which are crucial for assessing seismic hazard. However, there is still a scarcity of long-term, high-precision earthquake catalogs for the Anninghe–Daliangshan–Zemuhe Fault (ADZF). Based on the abundant phase data from Xichang dense seismic array and the China Earthquake Networks Center, we precisely relocated approximately 17,000 events using the double-difference relocation method, constructing an updated earthquake catalog for the ADZF. Our results reveal the complex structure of the ADZF, providing the detailed information of the dip angle and dip direction of different fault segments. The seismogenic layer depth of the Anninghe Fault is constrained to be less than 15 km, whereas the Daliangshan Fault had a notably deeper seismogenic layer, ranging from roughly 20 to 30 km in depth. Two significant locked segments were identified on the Anninghe–Zemuhe Fault: one in the Shimian–Mianning segment and another in the Mianning–Puge segment. Beneath Mianning, a zone of significant seismic activity extended from shallow depths down to approximately 10 km, separating the two locked segments. If the two segments ruptured independently, the possible maximum magnitudes for the Shimian–Mianning and Mianning–Puge segments should be M w 7.1 ± 0.2 and M w 7.3 ± 0.2, respectively. For the Shimian–Mianning segment, the fault locking pattern exhibited shallow locking and deep creeping, with the locking depth gradually increasing from north to south and showing heterogeneity along the fault strike. Overall, this study not only enhanced the precision of earthquake relocations, but also filled the gap in long-term seismic records of the region, offering insights into fault geometry, seismogenic layer depth, and locking distribution. Graphical Abstract