Abstract

Widespread coseismic change in pore-water pressure across a large alluvial fan in central Taiwan in the 1999 Chi-Chi (Mw = 7.5) earthquake was captured for the first time by a dense network of hydrologic monitoring wells. The complex, yet systematic, pattern in the water-pressure change appears inconsistent with the existing models; it requires a model that is based on the nonlinear mechanical behavior of sediments under earthquake shaking. This paper presents direct field evidence that earthquake shaking causes rising pore pressure in alluvial fans, which in turn may lead to landslides, even on very gentle slopes.

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