Source Complexity and Faulting Heterogeneity of the 2024 Mw 4.8 Zhongdian Earthquake, Yunnan, China

Abstract Earthquakes in stable continental regions occur less frequently than those at plate boundaries, and their seismic hazards remain poorly understood. In this study, we analyze the source complexity of the Mw 4.8 Zhongdian earthquake in southeastern Tibet, which occurred in an area where no major faults were previously mapped. Notably, the focal mechanism solutions differ significantly between the different approaches: whereas the centroid moment tensor (CMT) indicates oblique-normal faulting, the first-motion (FM) solution suggests purely dip-slip faulting. This discrepancy points to a complex rupture process involving multiple slip modes. Using multi-point-source inversion, we identify two near-simultaneous subevents. The first aligns with the FM dip-slip mechanism, and the second is dominated by strike-slip motion; together, they are consistent with the overall CMT solution. However, source spectral ratio analysis and displacement records show no distinct temporal separation between the subevents. On the other hand, structural complexities are revealed by relocated aftershocks and spatially diverse focal mechanisms, which enable the observed rupture behavior. We further compare the stress fields across multiple scales and find no significant differences in principal stress orientations between the Zhongdian source region and the broader western Chuandian block. Nevertheless, the two subevent areas display contrasting faulting styles, highlighting the influence of localized strain or deformation heterogeneity. These findings suggest that the moderate-size Zhongdian earthquake was governed by both complex fault geometry and heterogeneous faulting behavior.