[SCG61-P10] Mineralogical characteristics of fault rocks in the aftershock regions of the 2000 Western Tottori earthquake and its spatial distribution
Keywords:The 2000 Western Tottori earthquake, Fault rock, Mineral composition, XRD analysis
Mineralogical characteristics of rocks is one of the valid candidates that is likely to dominate its physical properties, and in general, increase in amount of frictionally weak minerals can reduce frictional strength of fault rocks. For understanding spatial slip behaviors in aftershock regions of the 2000 Western Tottori earthquake, we first need to investigate spatial variations in mineral composition of fault rocks. We collected more than 100 bulk rock samples from 14 fault-related outcrops, that distribute in northern, central, and southern parts of the aftershock regions. We then acquired XRD profiles of the powdered samples with internal standard (Al2O3) of 20 wt.%, and estimated the amount of minerals by using the RockJock software. The results clearly indicate that intact host rocks have similar mineralogical features regardless of sampling locations; they are granitic rocks composed of quartz, K-feldspar, and plagioclase. In contrast, mineral compositions of fault rocks show different characteristics by locations. In northern part of the aftershock regions, fault rocks are poor in K-feldspar and plagioclase and are rich in halloysite. In central part, fault rocks are poor in K-feldspar and plagioclase and are rich in illite. In southern part, fault rocks are poor in plagioclase and are rich in halloysite. These information tell us the representative mineralogical features of fault rocks in each part of the aftershock regions. Future friction experiments, by using representative fault rock samples under in-situ conditions, will give us a direct glimpse into the spatial variations of frictional properties in the aftershock regions of the 2000 Western Tottori earthquake, such as frictional strength and its velocity dependence. All of these information, not only seismological data but also mineral composition and physical properties of fault materials, should be incorporated for understanding the spatial heterogeneity of slip behaviors of the main shock and aftershocks of the 2000 Western Tottori earthquake.