On the basis of the assumption that ω2 model accords with source displacement spectra,we have obtained the mathematical expressions for calculating apparent stresses of moderate-small shocks from low-frequency flat level and corner frequency. By using digital seismic records,apparent stress values are calculated for 823 moder-ate-small shocks of 4 earthquake series in Yunnan area following corrections for instrument response,propagation influence and site effect. The results show that for the 4 earthquake series in Yunnan area,apparent stress hints precursory information,which means that if a moderate-small shock occurs with apparent stress larger than 1 MPa in an earthquake series,a moderate-strong earthquake will occur afterwards; and if there is not moderate-small shock with apparent stress larger than 1 MPa after a moderate-strong event in an earthquake series,strong after-shock will not occur. The research also indicates that the average apparent stress value is 0.8 MPa in Yunnan area,therefore,apparent stress is not obviously related to seismic magnitude.
展开▼
