Abstract The precursory waves before Wenchuan 8.0 earthquake are statistically tested by use of the observed strain data with the 4component borehole strainmeters at 16 stations around the epicenter.In which, first of all, the influence of solid tide whose period is longer than 128 minutes is removed with highpass filter,and the secondly,airpressure influence is removed with linear regression method, and then the signals for 2～128 minutes are decomposed into 6 different kinds of frequency bands with wavelet transform method. The results indicat that wavelet transform can be used to identify small change existed in deformation signal. On the basis of the characteristics of precursory wave indentified by wavelet transform,and the overrun rate method will be used to test the details of wavelet decomposing,and then the regression line slope of the overrun rate time sequence of entire details will be statisticed,thus the average and standard deviation can be obtained. These data show that precursory waves can not be generally detected during 15 day before earthquake.
