Source parameters and rupture directivity of the 2023 baoshan M_S5.2 earthquake in Yunnan, China

Accurate characterization of earthquake source parameters and rupture processes is crucial for seismic hazard assessment, yet moderate events in the complex fault zones of southwestern China remain poorly understood. To determine the source parameters and rupture directivity of the M_S5.2 Baoshan earthquake that occurred on May 2, 2023, in Yunnan, China, waveform data recorded by the Yunnan Seismic Network were used in combination with cut-and-paste, sPL depth‒phase identification, and relative centroid–rupture directivity inversion methods. Our results indicate that strike-slip faulting with a normal-slip component predominated both the mainshock (M_S5.2) and the largest aftershock (M_S4.6), with the optimal double-couple solution of the mainshock yielding nodal planes I: 49°/76°/–37° and II: 149°/54°/–163°. Both events occurred at a depth of 8 km, suggesting a shallow seismogenic fault with consistent geometry. Rupture directivity inversion indicated that the mainshock ruptured unilaterally along nodal plane II, propagating from southeast to northwest over ~3.8–4.3 km, consistent with the orientation of the isoseismal long axis. Based on the source parameters, rupture characteristics, and regional tectonic context, we infer that the seismogenic fault was likely the western limb of the Sanchongshan Fault, resulting in a shallow, moderate earthquake within the Lancangjiang Fault Zone. The integrated source parameter inversion employed in this study, which incorporates rupture directivity, enhances the accuracy of seismic hazard assessment and provides a valuable framework for future earthquake research.