The 2023 Mw 6.0 Jishishan Earthquake: A Slow Unilateral Rupture on a Blind Thrust Fault Revealed by High-Precision Earthquake Locations and Dynamic Modeling

Abstract The 18 December 2023 Mw 6.0 Jishishan earthquake struck the Dahejia basin in the northeastern Tibetan Plateau. Three isolated sites of concentrated fractures with a total length of ∼8 km were observed in field surveys. It remains unclear that such surface faulting was the extension of mapped active thrusts or just ground cracking. Moreover, inaccurate and incomplete routine earthquake catalog based on a sparse permanent seismic network makes it difficult to determine the seismogenic fault within a multifault zone. In this study, we develop a high precision aftershock catalog based on a self-deployed dense seismic array, illuminating an unrecognized blind northeast-dipping seismogenic fault and an activated southwest-dipping conjugate fault. We simulate the dynamic rupture process to investigate slip behaviors and delineate the previously suspected ruptures are ground cracking. Our results present a unilateral rupture event with a relatively slow rupture velocity and low radiation efficiency, suggesting that this earthquake may have ruptured an immature basin thrust.