HR: 11:50h
AN: T41E-07    [PDF]
TI: Fluidization of Fault During Slip: A Possible Mechanism of low Dynamic Friction During the 1999 Chi-Chi, Taiwan Earthquake and Implication for Seismic Slip Along the Splay Fault in the Nankai Accretionary Prism
AU: * Ujiie, K
EM: ujiiek@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kato, A
EM: akato@eri.u-tokyo.ac.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Trandafir, A C
EM: aurel@landslide.dpri.kyoto-u.ac.jp
AF: Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Sassa, K
EM: sassa@scl.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AB: The 1999 Chi-Chi, Taiwan earthquake (Mw7.6) caused a spectacular surface rupture along the Chelungpu thrust fault in the uplifted accretionary prism. The near-field strong-motion data obtained during this earthquake provided an invaluable opportunity to examine what dynamic process in the fault controls the large slip with low level of high-frequency seismic radiation. The Chelungpu fault drilling project involved drilling through the possible rupture zone within the upper 350 meters of the ground surface. Structural and physical property analyses of the possible rupture zone and high-velocity, undrained ring shear experiments using simulated material suggest that the fault was fluidized during the seismic slip. When the decay time of pore pressure in the fault due to diffusion in wall rocks is longer than duration of seismic slip, the fault composed of granular material in a loose state could lose frictional resistance due to fluidization. In general, unconsolidated material within the shallow portion of fault has a stable frictional slip property. However, if the shallow portion of fault is fluidized during earthquake, the seismic slip may propagate upward from seismogenic depths into the frictionless fault in a stable slip regime. This dynamic process appears to induce the seismic slip with low level of high-frequency seismic radiation during the Chi-Chi earthquake and may be applicable to fluid-saturated faults in accretionary prisms. We suggest that faulting under drained/undrained condition and consolidation state of fault before earthquake will control upward propagation of seismic slip from seismogenic zone into a stable slip regime.
DE: 7209 Earthquake dynamics and mechanics
DE: 8010 Fractures and faults
DE: 8025 Mesoscopic fabrics
DE: 8030 Microstructures
DE: 8045 Role of fluids
SC: Tectonophysics [T]
MN: 2003 Fall Meeting