Abrupt Along-Strike Change of Shallow Seismicity in Central and Southern Myanmar: Insights From High-Resolution Local-Earthquake Catalogs and Focal Mechanisms

Abstract

Myanmar's high seismic hazard is underscored by the 2025 Mw 7.7 earthquake on the Sagaing Fault, yet its seismicity patterns and underlying controls remain poorly understood. Using new seismic data from the 2nd-phase array of the China-Myanmar Geophysical Survey in the Myanmar Orogen, we construct a high-resolution catalog of 1,819 local-shallow earthquakes in central and southern Myanmar by combining deep-learning algorithms and manual phase-pick refinement, with 93 robust focal mechanisms. Integrated with a previous catalog further north, our analysis reveals that the Sagaing Fault dips eastward at ∼73° in the north, transitions to a nearly-vertical geometry at ∼20.5°N, and continues further south. This newly identified fault segmentation and associated geometric variations provide essential constraints for improving fine-scale rupture modelling of the 2025 earthquake. For the whole of Myanmar, our results suggest an abrupt along-strike north-south change of shallow seismicity across ∼20°N, with contrasting earthquake distributions and focal mechanisms.