Characterized source model of the 2013 Lushan earthquake (Mw 6.6) by the empirical Green’s function method

Abstract

Ground motions near the source area of the mainshock of the 2013 Lushan earthquake (Mw 6.6) in Sichuan Province in China were reproduced using the characterized source model and the empirical Green’s function method (EGFM). The best-fit characterized source model consisted of one strong motion generation area (SMGA) and a background area. The synthesized ground motions of the characterized source model were in fairly good agreement with the observed ground motions in the frequency range from 0.5 to 30.0 Hz at ten strong motion stations. For the 2013 Lushan earthquake (Mw 6.6), both the relationships between the SMGA and the seismic moment, and those between the flat amplitude of the acceleration source spectrum in the short period and the seismic moment almost followed the empirical scaling relationships of inner fault parameters developed for crustal earthquakes. The reasons for the largest peak ground acceleration (PGA) (> 1 g) in the strong-motion observation history of China recorded at the 51BXD strong motion station were investigated from the source and site effects. We found that the directivity effect did not contribute to the largest record by comparing the effect of different positions of the rupture starting point on the synthesized ground motions. The nonlinear effect of shallow layers was negligible, as indicated by the similarity of the earthquake H/V spectral ratios between the mainshock and EGF events. A large shear-wave velocity contrast might not exist in the shallow layers as the station was situated on the slope of a small rock hill. Finally, we agreed with previous studies that the hanging-wall effect and topographic effect might be the reasons for generating the largest record at Station 51BXD. Graphical Abstract