Preliminary High-Frequency Ground-Motion Scaling in Yunnan and Southern Sichuan, China

Abstract

A quantification of ground-motion scaling in the seismically active regions of the Yunnan and southern Sichuan provinces of China is an essential com- ponent for the evaluation of seismic hazard there. The significance of the regional hazard is emphasized by the effects of the 2008 Wenchuan earthquake in nearby cen- tral Sichuan province. We approach the ground-motion scaling problem by using recordings of 474 small earthquakes with local magnitudes between 3.0 and 5.5 in the 0.3-12 Hz frequency range. Although we had limited observations at hypocentral distances less than 50 km, we derived an absolute ground-motion scaling model for distances of 50 to 400 km. After defining a geometrical spreading function, we found that a Qf �� 180f 0:50 , an average site κ � 0:025 s for the vertical component, and a Brune stress drop of Δσ � 3 MPa adequate to model our observations. The stress- drop value was constrained by independently determined seismic moments. In lieu of a significant strong motion data set in the study region, the parameters derived form the basis for stochastic modeling of peak ground motions for hazard studies