Areal strain and hydrological changes in Taiwan induced by 2008 Wenchuan earthquake

The Mw 7.9Wenchuan earthquake of 12 May 2008 was the most devastating earthquake in China in the past 30 years in terms of human losses and property damage. The main shock ruptured with about 9 m of slip along the Longmen Shan fault zone located the boundary of Tibetan plateau and Sichuan basin. About 5-6 m maximum vertical offset was identified in the field survey after the earthquake. Nine borehole strainmeters installed at western Foothills in Taiwan orogenic belt captured significant step-like variation of areal strain. The areal strain increasing was observed from 0.01 to 0.2 microstrain at five boreholes located in Chiayi area southwestern Taiwan and Hisnchu area northwest Taiwan. The areal strain decreasing was also observed from 0.05 to 4 mricostrain at three boreholes located at Hisnchu and Taipei area of northwest Taiwan. This big earthquake also case water level to sscillate and undergo sustained changes occurred concurrenly with S waves and Love waves. We attribute these step-like transient variations of areal strain to the dynamic triggering of the Wenchuan earthquake.