Stress Field Changes before the M S 8.0 Wenchuan Earthquake

The apparent lack of pre-seismic crustal deformation preceding the 2008 Ms8.0 Wenchuan earthquake has been the subject of debate. In this study, tiltmeter data recorded close to the earthquake epicenter were analysed using spectrum and wavelet analysis. Changes in the stress field before the earthquake were analyzed based on the Benioff creep release and changes in regional Global Navigation Satellite System (GNSS) baselines. The characteris-tics of far- and near-field seismicity and deformation processes were investigated using rock fracture experiments. The results show that during pre-seismic strain energy accumu-lation, there was a synergy between stress field changes both proximal and distal to the ep-icenter; moreover, we identified a strong correlation between Benioff creep release and shortening of the LUZH-GUAN GNSS baseline. During the sub-instability stage, the de-formation characteristics of different structural sectors differed; faults near the epicenter were in a highly locked state, and the deformation rate and wave spectra of main period waves obviously decreased. This reflects fixed point deformation driven by deep stress. These results are of great significance for understanding geophysical field observations, for clarifying pre-seismic deformation and for earthquake prediction.