A study on S wave splitting using waveform data from Shanxi reservoir induced earthquakes in Wenzhou of China

Abstract:more than 1000 earthquakes induced by the Shanxi reservoir in Wenzhou, Zhejiangprovince of China, were recorded by both Zhejiang regional digital seismic network and Shanxi reservoir local digital network during the period from Feb. 4 to Oct. 31, 2006. Using wave form data of these earthquakes we studied S-wave splitting characteristics in the reservoir region. The earthquakes were relocated and the S-wave records with travel paths within S-wave window were selected out for analysis. The fast wave polarity azimuth and the slow wave time delay were determined by using the technique of cross-correlation coefficient analysis. The result indicates that S waves coming from the reservoir earthquakes show notable splitting. The average fast wave polarization azimuth obtained at different stations generally coincides with the orientation of regional maximum principal stress therein. In Shanxi reservoir region the average polarization azimuth of fast S wave is nearly in N-S direction. The scattering and spatial variation of the deduced fast S wave polarity may be attributed to the effect of local structure inhomogeneity. Presently the stress field in the reservoir region has recovered to stable state, and there would be little possibility of occurrence of a next strong earthquake.