Earthquake fault rock indicating a coupled lubrication mechanism
20 Dec 2006
1Department of Earth and Planetary Science, the University of Tokyo, Hongo 7-3-1, Bunkyo-Ku, Tokyo, 113-0033, Japan
2The Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima 2-15, Natsushima-cho, Yokosuka-city, Kanagawa, 237-0061, Japan
3Institute of Geoscience, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577, Japan
Abstract. A pseudotachylyte bounded by a carbonate-matrix implosion breccia was found at a fossilized out-of-sequence thrust in the Shimanto accretionary complex, Japan. This occurrence resulted from the following events: first implosion of host rock due to interstitial fluid pressure increase and asymmetric fracturing; second, Ca-Fe-Mg carbonate precipitation; and third, frictional melting. The rock-record suggests that these events took place in a single seismogenic slip event. Resulting from abrupt drop in fluid pressure after implosion, hydro-fracturing and fluid escape, recovered high effective friction promoted melting during fault movement. Coexistence of fluid implosion breccia and pseudotachylyte has never been reported from continental pseudotachylytes, but might be characteristic from hydrous seismogenic faults in subduction zones.