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

A quantification of ground-motion scaling in the seismically active regions of the Yunnan and southern Sichuan provinces of China is an essential component 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 central 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 Q (f) = 180f(0.50), an average site. kappa = 0: 025 s for the vertical component, and a Brune stress drop of Delta sigma = 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