On the short-term precursory phenomena of ground deformation associated with the 2008 M S8.0 Wenchuan earthquake

The 12 May 2008 MS8.0 Wenchuan earthquake is one of the most catastrophic event in the past 60 years in China.Great attention has been paid by a lot of scholars.In this paper,we studied the pre-seismic deformation characteristics of ground tilt along the earthquake rupture zone and leveling across the rupture zone.We showed that before the eartthquake some tiltmeters installed along the Longmenshan seismic belt were in operation and no significant changes have been observed at Kangding,Wenchuan and Maoxian stations,and there were also no reliable precursors among 6 cross-fault levelling observation sites,except the large changes observed at the Gengda site which has been denied as a precursor anomaly by mathematical modelling.We analyzed the regional seismic activity data and significant deformation anomalie on South-northern seismic belt,and studied the strain accumulation process of Wenchuan earthquake.We proposed that no significant short-term precursory changes around the epicentral area was possibly related to the properties of high-strain but small deformation state prior to the main shock,but the factors of deformation measurement sites and the kinds of measurement instruments could not be excluded.