Earth Planets Space, Vol. 54 (No. 11), pp. 1211-1218, 2002
Bunichiro Shibazaki1, Hidemi Tanaka2, Haruo Horikawa3, and Yoshihisa Iio4
1International Institute of Seismology and Earthquake Engineering, Building Research Institute, Tatehara 1, Tsukuba, Ibaraki 305-0082, Japan
2Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113-0033, Japan
3Active Fault Research Center, National Institute of Advanced Industrial Science and Technology, Site 7 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
4Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Japan
(Received January 16, 2002; Revised August 20, 2002; Accepted August 29, 2002)
Abstract: The fault zone in the earth's crust is thought to consist of several regions from top to bottom: the upper frictional region, the brittle-ductile transition zone and the ductile region. The upper frictional region consists of the unstable frictional zone, the unstable-stable transition zone, and the stable frictional zone. Recent geological observations of fault rock suggest that at the deeper part of the seismogenic zone, co-seismic frictional slip coexists with interseismic flow processes. We propose a possible model for slip processes at the deeper part of the seismogenic zone in which the frictional slip and flow processes are connected in series. In this model, in the ductile region, power law creep is dominant. Around the unstable-stable transition zone, we assume that co-seismic frictional slip coexists with aseismic flow processes. We investigate simple 1-D and 2-D models where rate- and state-dependent friction coexists with power law creep that has a threshold stress. The results of numerical simulations show that the amount of slip during the interseismic period is greater in the case where friction coexists with power law creep than it is when only friction is at work. It is also found that, for the case where friction coexists with power law creep, frictional slip is largely inhibited in the ductile region.