Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6444923 | Journal of Structural Geology | 2014 | 26 Pages |
Abstract
We document regional pore-fluid pressures in the active Taiwan thrust belt using 55 deep boreholes to test the classic Hubbert-Rubey hypothesis that high static fluid pressures (depth normalized as λ = Pf/Ïrgz) account for the extreme weakness of thrust faults, since effective friction μfâ=μf(1âλ). Taiwan fluid pressures are dominated by disequilibrium compaction, showing fully compacted sediments with hydrostatic fluid pressures at shallow depths until the fluid-retention depth zFRD â 3 km, below which sediments are increasingly undercompacted and overpressured. The Hubbert-Rubey fault weakening coefficient is a simple function of depth (1 â λ) â 0.6zFRD/z. We map present-day and pre-erosion fluid pressures and weakening (1 â λ) regionally and show that active thrusts are too shallow relative to zFRD for the classic Hubbert-Rubey mechanism to be important, which requires z â¥Â â¼4zFRD â 12 km to have the required order-of-magnitude Hubbert-Rubey fault weakening of (1 â λ) â¤Â â¼0.15. The best-characterized thrust is the Chelungpu fault that slipped in the 1999 (Mw = 7.6) Chi-Chi earthquake, which has a low effective friction μfââ0.08-0.12, yet lies near the base of the hydrostatic zone at depths of 1-5 km with a modest Hubbert-Rubey weakening of (1 â λ) â 0.4â0.6. Overpressured Miocene and Oligocene detachments at 5-7 km depth have (1 â λ) â 0.3. Therefore, other mechanisms of fault weakening are required, such as the dynamical mechanisms documented for the Chi-Chi earthquake.
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Physical Sciences and Engineering
Earth and Planetary Sciences
Geology
Authors
Li-Fan Yue, John Suppe,