Stress measurements in the Scientific Drilling Projectof 2008 Wenchuan Earthquake Fault, China

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To investigate relations of fault rupturing during a great earthquake and stress change, we tried to determine in situ stress state both in Wenchuan Earthquake Fault Scientific Drilling Project (WFSD) and in Japan Trench Fast Drilling Project (JFAST) penetrating through the fault ruptured during 2011 M9 Tohoku-Oki earthquake. We found that in-situ horizontal stress in the vicinity of the Tohoku-Oki earthquake fault decreased during the earthquake distinctly. The stress change suggests an active slip of the frontal plate-interface consistent with coseismic fault weakening and a nearly total stress drop.