On the Characteristics of Ground Deformation Anomalies in the Middle and Northern Part of the South-North Seismic Belt prior to the Wenchaun Earthquake

This paper analyzes the characteristics of observed ground tilts and strains near and around the Wenchuan earthquake rupture zone,and of the measured changes of Longmenshan,Xianshuihe and Qilian seismic belts.The observed phenomenon demonstrated that the ground tilt velocities at Ya'an,Wenchuan and Maoxian sites turned abruptely in the beginning of 2006,and then decreased steadily up to the occurrence of Wenchuan earthquake.The five sites for cross fault measurement on the Longmenshan seismic belt,the great change was only observed on Gengda site,but the change maybe caused mainly by the new buildings near the site.A rapid change durated for three months was observed by the fault creep-meter at the Longdengba site 220 km away from the epicenter,which gives us information for an M6.5 earthquake in three to four months after the rapid change ended.Great changes were also observed using fault leveling on the Qilian seismic belt,the question if they were related to the Wenchuan earthquake is to be studied.