Seismic Refraction Studies Of Weathered Volcanic Slopes For Characterizing Rainfall-Induced Landslide Potential

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Department of Geological and Mining Engineering and Sciences


Seismic refraction surveys were conducted on steep slopes of San Vicente Volcano, El Salvador, adjacent to the 2009 Hurricane Ida triggered failures and in areas that experienced surface cracks during Tropical Depression 12E in 2011. Surveys were conducted at the ends of the dry and rainy seasons in an attempt to discern changes in soil moisture and perched water tables. The survey design and execution were focused on high-resolution characterization to discern layering. The results were very precise and reproducible. Layering was evident in four of the six surveys collectively for the three sites. One site exhibited no apparent layering over the depth of study. The other sites showed layering but no apparent presence of a water table in either season, but a higher moisture content was observed at the end of the rainy season. Likely that the permeability of the deposits and the steepness of the slopes prevent a perched water table except for extreme rain events, which are associated with named storms. Shear-wave refraction surveys were also performed which yielded no additional insights into subsurface conditions but did provide direct measurements of shear wave velocities that were used to mathematically explore plausible scenarios for changing moisture and depth.

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