Source Mechanism and Rupture Directivity of Small Earthquakes in the Changning Region, China, Using Dense Array Data

Abstract Integrating focal mechanism solutions with rupture directivity analysis enables high-resolution characterization of subsurface fault geometry and earthquake rupture processes. However, resolving these parameters for small-magnitude earthquakes remains challenging due to small rupture sizes, short durations, and low signal-to-noise ratio. Here, we utilized a dense array of nodal seismometers in the Changning region, Sichuan basin, China, to study the focal mechanism and rupture directivity of aftershocks following the 2019 Ms 6.0 earthquake. Using PhaseNet+ and SKHASH, we first enhance the focal mechanism catalog (1 1), and their spatial variability reflects a long-term interplay between fluid injection and faults in the salt-mining area. These findings illuminate a complex fault system beneath the Changning anticline and highlight the importance of high-resolution seismic arrays in resolving rupture processes of small-magnitude events.