2007 Ground Water Summit

Monday, April 30, 2007 : 1:00 p.m.

Seismic Shear Wave Reflection Characterization of Aquifers: An Example from the Former Fort Ord, Monterey, California

Seth S. Haines, Ph.D. and Karl J. Ellefsen, Ph.D., U.S. Geological Survey

The seismic shear wave reflection method offers sensitivity to heterogeneity in aquifer mechanical properties (e.g. stratigraphic layering) without interference from saturation variations or other pore-fluid properties.  It is well-suited to imaging unconsolidated sediments such as at the former Fort Ord, in Monterey County, Calif., where the upper 100 m of geology consists of sand and gravel aquifers separated by silt and clay aquitards.  In order to help guide cleanup efforts, the US Geological Survey has undertaken seismic shear and compressional (P) wave reflection surveys at the site.  Sledgehammer-source SH- (horizontally polarized shear) wave data show reflections from interfaces up to approximately 60 m deep, and delineate the major aquifer/aquitard boundaries.  In contrast, P-wave seismic data show only the reflection from the water table at approximately 30 m depth.  The SH-wave images agree with available borehole information and provide additional information between and beyond areas with boreholes.  This study demonstrates the effectiveness of SH reflection methods for imaging aquifer stratigraphy and for providing groundwater modeling constraints.

Seth S. Haines, Ph.D., U.S. Geological Survey Seth Haines received his BA (geology and physics) from Middlebury College in 1997. He received his M.S. (2001) and Ph.D. (2005) in the Geophysics Department at Stanford University, first studying the tectonic evolution of the Tibetan plateau using seismic refraction methods, and then working to develop seismoelectric experimental methods for use in near-surface applications. He is currently a Mendenhall Postdoctoral Research Fellow with the U.S. Geological Survey in Denver, CO, working primarily on shear-wave seismic reflection imaging of near-surface targets.

Karl J. Ellefsen, Ph.D., U.S. Geological Survey Karl J. Ellefsen works for the U.S. Geological Survey as geophysicist. He specializes in geophysical methods related to seismic and radar wave propagation, and he uses these methods to characterize both unconsolidated sediments and bedrock. He is especially interested in characterization related to ground water and contaminants.


The 2007 Ground Water Summit