Imaging of high-frequency energy radiation of the 2013 Lushan Mw6.6, China, earthquake by envelope inversion

Abstract

The reliability of high-frequency energy radiation source inversion is constrained by the quality of the available seismic records. To obtain a robust inversion for the Lushan earthquake, we first determined through resolution analysis that the maximum resolvable subfault size is 10 km × 10 km, corresponding to 20 inversion parameters given the six near-fault stations. Using envelope inversion via the differential evolution algorithm, we obtained the high-frequency radiation distribution on the fault. The results show that roughly half of the fault plane generated significant high-frequency radiation, concentrated primarily around the main asperity and along the fault edges. The strongest radiation patch is located 10 km northeast of the hypocenter at a depth of about 7 km (spanning 3–12 km depth) and covers 400 km², accounting for 40% of the total radiating area. The remaining 60% of the radiation is distributed along the rupture periphery. Regions of strong high-frequency radiation generally correlate with higher rupture velocities. The high-frequency radiation of the Lushan earthquake is predominantly concentrated in the shallow crust with 3–12 km depth, exhibiting clear spatial and depth separation from the main slip zone located at 15 km depth. This pattern suggests significant vertical mechanical differentiation in energy release within this blind thrust fault system.