Estimation of seismic stress drop from the peak velocity of ground motion

Abstract

According to the source dislocation model suggested by Brune(1970), the authors have calculated the displacement spectra of S-wave and source parameters of the Heqing Ms 5.3 earthquake sequence, using the digital data of this sequence obtained in the Western Yunnan Earthquake Prediction Experimental Field (WYEPEF). Based on this calculation we have studied the dependence of the peak velocity (rv) of ground motion on the seismic stress drop Δσ. From the seismic scaling law we obtained (rv) ∞Δσ2/3, thus the three formulae of calculating seismic stress drop Δσ using the peak velocity parameters can be derived: lg(rv)=d1+1/3lgM0+2/lgΔσ lg(rv)=d2+1/3ML+2/3lgΔσ=-1.0+1.5lg(rv). Assuming that the average stress drop Δσ=3.0×106 Pa for great and small earthquakes, then the constants d1= −3.88 and d2=−0.38 are determined by the observational data of the Heqing Ms5.3 sequence. Results of the source parameters for this sequence show that the seismic moment M0 is between 1011 N · m and 1015 N · m, the rupture radius a of the source is between 200 m and 600 m, the stress drop Δσ is between 0.1 MPa and 10 MPa and the average stress drop Δσ=3.7 MPa calculated from the peak velocity parameter of the ground motion. Δσ values measured from these scaling relations are basically in agreement with the results given by Brune’s method (1970). Results of this study show that the dependence of the ground motion peak velocity parameter (rv) on the stress drop Δσ is even stronger than that on the seismic moment M0.