HR: 14:25h
AN: T43D-04 INVITED     [Abstracts]
TI: Permeability of Whole Core Samples of Chelungpu Fault, Taiwan TCDP Scientific Drillhole
AU: * Lockner, D A
EM: dlockner@usgs.gov
AF: US Geological Survey, ms/977 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Morrow, C
EM: cmorrow@usgs.gov
AF: US Geological Survey, ms/977 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Song, S
EM: srsong@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University P.O. Box 13-318, Taipei, 106 Taiwan
AU: Tembe, S
EM: stembe@ic.sunysb.edu
AF: Dept. of Geosciences, SUNY Stony Brook, Stony Brook, NY 11794 United States
AU: Wong, T
EM: Teng-fong.Wong@stonybrook.edu)
AF: Dept. of Geosciences, SUNY Stony Brook, Stony Brook, NY 11794 United States
AB: We are measuring material properties of core samples from the 2000 meter Taiwan Continental Drilling Program (TCDP) borehole crossing the Chelungpu fault (activated during the 1999 M7.6 Chi-Chi earthquake). Measurements include permeability, intact strength, frictional sliding strength and poroelastic storativity. Initial tests are concentrating on permeability and storativity of undisturbed whole core samples spanning approximately 60 m including the main shear zones identified at depths of 1111 m and 1151 m. The 1111 m shear zone is believed to have slipped nearly 10 meters during the Chi-Chi earthquake. Formation rock types vary from shales to mudstones to graywacke. Pervasively high clay content throughout the core suggested that samples would be sensitive to salinity of the pore fluid used during testing. This was confirmed by spot tests of strength and permeability versus pore water salinity. (Increased salinity increased strength, Young's modulus and permeability.) Consequently, all TCDP samples were tested with 1 molar KCl pore fluid. Permeability results are therefore expected to represent upper bounds on in-situ values. Whole core permeabilities measured at 15.5 MPa effective confining pressure (appropriate for 1111 m depth) ranged from 0.4 to 7 x 10^-20 m², with the lowest values near the axis of the 1111 m shear zone. At this same effective pressure, storativity was in the range 1.3 to 7 x 10^-11 Pa^-1 and preliminary measurements of coefficient of friction were 0.55 to 0.75. Apparently, even fault `core' samples contain sufficient quartz and other hard grains to sustain moderate to high frictional strength. The northern segment of the Chi-Chi earthquake which slid on the Chelungpu fault showed an unusual combination of suppressed high frequency seismic radiation and large total slip, leading to the suggestion that deformation was enhanced by high transient pore fluid pressure. Our observations of low permeability, low storativity and high frictional strength make this section of the Chelungpu fault a good candidate for thermally-induced fluid pressurization and dynamic weakening during the Chi-Chi earthquake.
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005