Earth Planets Space, Vol. 54 (No. 11), pp. 1085-1090, 2002
Yoshihisa Iio1 and Yoji Kobayashi2
1Earthquake Research Institute, the University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan
2Institute for Geoscience, University of Tsukuba, Tsukuba, Ibaragi 305-0006, Japan
(Received December 30, 2001; Revised July 29, 2002; Accepted August 23, 2002)
Abstract: The cut-off depth of seismicity in and around the Nojima fault broken by the 1995 Kobe earthquake occurring in the intraplate Japan was compared with a brittle-ductile transition depth of the widely-accepted strength profile model of the crust. It was found that the cut-off depth is much deeper than the transition depth under the assumption that wet granite is deformed at a strain rate of 10-15/s. Such a small strain rate implies that the plastic flow is uniformly distributed below the seismogenic region. When the strain rate is assumed to be greater than 10-13, the cut-off depth can be attributed to the transition depth. This suggests that deformation is localized in a narrow fault zone below the seismogenic region even in the intraplate region.