HR: 09:45h
AN: S11E-08    [Abstracts]
TI: Dynamic Mechanochemistry of Seismic Slip -Nano Spherules Lubrication
AU: * Tanaka, H
EM: tanaka@eps.s.u-tokyo.ac.jp
AF: The University of Tokyo, Graduate school of Science, Hongo 7 - 3 - 1, Bunkyo-ku, Tokyo, 1130033, Japan
AU: Chen, W
EM: dc@geps.gep.ncu.edu.tw
AF: National Central University, Taiwan, No.300, Jhongda Rd., Jhongli City, Taoyuan, 32001, Taiwan
AU: Chen, Y
EM: porterchen@nsrrc.org.tw
AF: National Synchrotron Radiation Research Center, Taiwan, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu, 30076, Taiwan
AU: Song, Y
EM: song@nsrrc.org.tw
AF: National Synchrotron Radiation Research Center, Taiwan, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu, 30076, Taiwan
AU: Ma, K
EM: fong@earth.ncu.edu.tw
AF: National Central University, Taiwan, No.300, Jhongda Rd., Jhongli City, Taoyuan, 32001, Taiwan
AB: The Chelungpu fault, which was activated during 1999Chi-Chi Earthquake, had been drilled (Hole A, B and C) to recover the earthquake slip zone materials. We present here the results of nano-scale observations for identified slip zone materials (Ma, Tanaka et al., 2006) by using HR-TEM and TXM technique. Minimum size of grains observed under HR-TEM is 3 nm. The grain size distribution for grains larger than 100 nm in diameter follows the fractal law and grain shape is highly irregular. Grains smaller than100 nm show some specific characteristics, that is, smaller the grains, more the spherical shapes and more equi-granular. Thus, the grains smaller than 100 nm are no longer described by fractal distribution model. By SAD and EDX analysis under HR-TEM, the nano spherules are mainly composed of crystallized quartz associated with minor amounts of carbonates and amorphous materials. Results of observations lead following three conclusions, (1) nano spherules are not generated just by fracturing based on their shapes and grain size distributions. (2) nano spherules would compose viscous materials enveloping larger fractured grains from SEM observations. (3) Mica clay minerals and feldspars are disappeared in ultra-fine grained layer. This implies that chemical process of dissolution - elements dissipation - SiO2 precipitation occurred associated with mechanical fracturing. Therefore nano spherules would be generated through mechano-chemical process during co-seismic slip. Dynamic shear strength drop by rapid slip experimentsare and formation of gelled materials are recently reported. Large differences of ultra-fine products between previous reports and our observations are existence of nano spherules and their crystallinity. If the nano- spherules are generated during seismic slip, dynamic weakening would be expected because mode of friction turns into rolling friction by huge amounts of equigranular and spherical grains. This may be alternative explanations for dynamic weakening. Quantitative process of dynamic fracturing will be discussed in our presentation.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 7209 Earthquake dynamics (1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8034 Rheology and friction of fault zones (8163)
SC: Seismology [S]
MN: 2007 Fall Meeting