Abstract
AbstractTectonically active coastal margins commonly host landslides that are influenced by hydrologic, geologic, and/or anthropogenic perturbations. The work reported here is motivated by the hydrologically driven, deep‐seated bedrock slides that intersect the (former) Pacific Coast Highway in the active landslide zone at Devil's Slide near Pacifica, California. Numerical simulation of subsurface flow is employed to investigate saturated zone fluid pressure scenarios for 3‐D Devil's Slide‐like systems. The four‐phase concept‐development effort is comprised of 134 hydrogeologic simulation scenarios which investigate fluid pressure response for complex subsurface conditions and historically based climate forcings. Recharge, heterogeneity, and anisotropy are shown to increase fluid pressures in targeted failure‐prone locations by up to 73.8, 10.3, and 1.8 %, respectively. The interaction between fault zone characteristics and topographically driven flow are shown to influence fluid pressures for up to 85% of the approximately 7.0 105 m2 study area. Simulated fluid pressures support the known slope instability for the Devil's Slide site. A quantitative hypothesis‐testing discussion explores the likelihood of perched water above the regional water table at the site. Further understanding of hydrologically driven slope movement in the active landslide zone will require additional data focused on rigorous characterization of the unsaturated zone.
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