Co-seismic Gravity Change of M_w 7.9 Wenchuan Earthquake and Pre-Seismic Gravity Anomaly Detection by Superconducting Gravimeter at Hsinchu, Taiwan, from April to June 2008

Earthquakes are caused by crustal movement that releases a huge amount of energy and leads to deformation. The gravity near the epicenter is changed by the deformation of rock materials. Precursors may be detected during the period of seismogenic activity. On 12 May, 2008, a M _w 7.9 earthquake struck near Wenchuan in China. A co-seismic gravity offset of 10.5μGal and a pre-seismic gravity anomaly about 2 days before the main shock was found in gravity records of the superconducting gravimeter (SG) at Hsinchu, Taiwan. SG records from April to June 2008 were used in this study. During this period of time, 8 gravity anomaly events caused by earthquakes were found. Sonograms of time-frequency analysis show that the perturbations occurred in 1-2 major bands (0.1-0.15Hz and 0.2-0.3Hz). The results of canonical correlation analysis show a significant positive correlation between the duration of gravity perturbation before the main shock and the magnitude of the earthquake. This study suggest that SG is a promising instrument for the analysis of earthquake events.