HR: 13:55h
AN: T43D-02 INVITED     [Abstracts]
TI: Slip Zone and Energetic of a large earthquake from seismological modeling and fault core of TCDP
AU: * Ma, K
EM: fong@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Chung-Li, 320-54 Taiwan
AB: Taiwan Chelungpu-Fault Drilling Project (TCDP) drilled two holes 40 m apart (a continuous coring of 500m to 2000m in hole-A, and 950m to 1300 m in hole-B) into the northern portion of the recently ruptured large slip zone of the Chelungpu fault. The principal slip zone, PSZ, was identified at the depths of 1111.23 to 1111.35 m in hole-A, and a corresponding feature was identified in hole-B at the depths of 1136.50 to 1136.62 m, consistent with geological observations at the surface. The vertical extent of the damage zone relative to the fault core is asymmetric, with a greater thickness above the fault core. The PSZ is about 12 cm thick and located near the lower boundary of the damage zone and contains subsidiary cataclastic fracturing. The geophysical logging showed the measurements of low seismic velocities and low electrical resistivity in the vicinity of the identified PSZ. Along with the orientation of observed fractures, the geophysical features support that the deformed zone at 1111m is the primary fault zone. The actual grain sizes from the gouge layer of the core were measured from transmission electron microscopy (TEM) and shown to have diameters of 10 nm to 300 nm. The seismic fracture energy calculated from the dense strong motion waveforms for the fault block beneath the drill site is 11.6 MJ/m2. It yields the radiated efficiency of 0.5, which is intermediately compared with the values from Punch bowl fault and South African mine. If there was only a fraction of the seismic fracture energy contributes to the creation of the gouge, the number of repeated earthquakes in the PSZ could be 10, 100, and 1000, respectively, for the fraction of 1, 0.1, and 0.01. The corresponding values on the ratio of gouge thickness to the accumulated slips (T/D) would be 1.44x10-3, 1.44x10-4, and 1.44x10-5 if we consider the slip of 8.3 m as the Chi-Chi earthquake for every repeated earthquake. The former two values of T/D are comparable to the geological data. It­Ýs likely that the number of repeated earthquakes in the PSZ was formed by tens of events. It might suggest that the earthquakes were not repeatedly occurred on the same slip zone in the entire history of the fault. Comparing to other observations in various faults, our results suggest that the amount of energy needed to form a fault zone probably depends on the maturity and style of faulting.
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005