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In-situ measurement of the hydraulic diffusivity of the active Chelungpu Fault, Taiwan

Mai Linh Doan, Emily E. Brodsky, Yasuyuki Kano, & Kuo-Fong Ma

Published August 2006, SCEC Contribution #1071

Hydraulic diffusivity controls fluid pressure and hence affects effective normal stress during rupture. Models suggest a particularly spectacular example of fluid pressurization during the M w = 7.6 1999 Chichi earthquake when pressurization may have reduced high-frequency shaking in the regions of large slip if the fault was sufficiently sealed. We investigate in situ hydraulic diffusivity which is the key parameter in such models through a cross-hole experiment. We find a diffusivity of D = (7 ± 1) × 10−5 m2/s, which is a low value compatible with pressurization of the Chelungpu fault during the earthquake. In most poroelastic media, the hydraulic storativity S lies between 10−7 and 10−5, so that the transmissivity T along the fault zone is comprised between 10−11 m2/s and 10−9 m2/s. The corresponding permeability (10−18–10−16 m2) is at most one hundred times larger than the value obtained on core samples from the host rock. The fault zone is overpressurized by 0.06 to 6 MPa, which is between 0.2% and 20% of the lithostatic pressure.

Doan, M., Brodsky, E. E., Kano, Y., & Ma, K. (2006). In-situ measurement of the hydraulic diffusivity of the active Chelungpu Fault, Taiwan. Geophysical Research Letters, 33, L16317. doi: 10.1029/2006GL026889.