T43G-02
JFAST Constraints on the Tohoku Earthquake Fault
Thursday, 17 December 2015: 13:55
104 (Moscone South)
Emily E Brodsky, University of California Santa Cruz, Santa Cruz, CA, United States, James J Mori, Kyoto University, Kyoto, Japan, Frederick M Chester, Texas A & M University, Geology & Geophysics, College Station, TX, United States, Shuichi Kodaira, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan and IODP Exp 343/343T
Abstract:
The Japan trench fast drilling expedition (JFAST) demonstrated that the fault zone of the Mw 9.0 Tohoku earthquake at the drill site near the trench was weak during slip. Four different lines of evidence led to this conclusion: (1) the low temperature anomaly on the fault zone, (2) the stability of the borehole indicating low deviatoric stress, (3) the high fraction of scaly clay in the narrow fault zone in the core, and (4) laboratory experiments on recovered fault material showing low friction under undrained conditions. Recent measurements of low temperature from the Wenchuan Fault Zone scientific drilling project suggest that friction may have been low at that site as well. The evidence for low deviatoric stresses during slip favors an asperity model where failure is determined by locally strong spots in a pervasively weak fault. During the 9-month JFAST observatory deployment, a rich array of behavior after the earthquake was revealed including evidence for fluid pulsing through the fault zone in response to local aftershocks. Capturing the healing and relocking of a fault zone is still an open challenge to fault zone drilling.
