HR: 0800h
AN: T11A-0355    [Abstracts]
TI: Scanning ESR microscopy revealing multiplex frictional heating events in the Nojima fault rocks, Japan
AU: * Fukuchi, T
EM: fukuchi@yamaguchi-u.ac.jp
AF: Yamaguchi University, 1677-1 Yoshida, Yamaguchi, 753-8512, Japan
AB: Whether or not the temperature rise due to frictional heating in a fault zone universally occurs is a significant problem in connection to the San Andreas fault heat flow paradox or the earthquake energy budget. Since paramagnetic iron hydroxides (γ-FeOOH or Fe(OH)₃) inside the fault gouge change into ferrimagnetic iron oxides, maghemite (gamma-Fe₂O₃), by frictional heating [Fukuchi, 2003; Fukuchi et al., 2005; 2007], ferrimagnetic minerals in fault rocks are available as indicators of ancient frictional heating events. I thus started detecting FMR (ferrimagnetic resonance) signals derived from ferrimagnetic minerals in fault rocks using a scanning ESR (electron spin resonance) microscopy technique. In the scanning ESR microscopy, microwaves leaking out of a pinhole bored on a cavity resonator are directly absorbed by a flat slab sample, and continuous ESR data or ESR images are obtained by one- or two-dimensionally moving the slab sample with an X-Y stage. At the present stage, the resolution for detection is estimated as 0.25mm in using a 2.6mmφ pinhole. This resolution is enough to detect ancient frictional heating events recorded in natural fault rocks although frictional heat temperature changes at a unit of 1 mm or less with the distance from a fault plane. As a result of scanning ESR microscopy of the Nojima fault rocks in Japan, I have succeeded in detecting multiplex frictional heating events recorded in the fault gouge and pseudotachylyte. I now attempt to reconstruct the temperature of ancient frictional heat by inversion using each FMR signal peak showing the multiplex frictional heating events. A preliminary computer simulation indicates that the temperature rise due to frictional heating has universally occurred in the Nojima fault zone and the maximum temperature during ancient seismic fault slips may have momentarily risen above 1000°C. References Fukuchi, T. (2003) J. Geophys. Res., 108, No.B6, 2312, doi:10.1029/2002JB002007. Fukuchi, T., Mizoguchi, K., and Shimamoto, T. (2005) J. Geophys. Res., 110, B12404, doi:10.1029/2004JB003485, 2005. Fukuchi, T., Yurugi, J., and Imai, N. (2007) Tectonophysics, doi:10.1016/j.tecto.2007.01.020.
UR: http://web.cc.yamaguchi- u.ac.jp/~fukuchi/
DE: 1540 Rock and mineral magnetism
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 5109 Magnetic and electrical properties (0925)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2007 Fall Meeting