USGS Groundwater Information: Branch of Geophysics
USGS scientists Fred Stumm (left) and Tony Chu (right) monitor data on laptop while testing seismometer in New York. (The seismometer is the gray cylinder in the left side of the photo.)
Estimating sediment thickness and the geometry of the bedrock surface is a key component of many hydrogeologic studies. Some studies do not require or cannot support the expense of high-resolution continuous geophysical data and would benefit from an inexpensive method capable of rapidly providing a robust estimate of bedrock depth at a point. The horizontal-to-vertical spectral ratio (HVSR) seismic method is a novel, non-invasive technique that can be used to rapidly estimate the depth to bedrock.
Initial applications of the method by the USGS Office of Groundwater, Branch of Geophysics (OGW BG) indicate that the HVSR seismic method is a promising method for local- to basin-scale mapping of bedrock geometry; mapping Quaternary geology; and delineation of buried valleys, channels, and faults. In 2009, with support from the USGS Groundwater Resources Program, the USGS Office of Groundwater, Branch of Geophysics conducted an HVSR seismic technology demonstration/evaluation project to evaluate the use of the method to support hydrologic studies, particularly the development of conceptual and numerical groundwater flow models. As part of this project, the USGS conducted pilot studies across the Nation.
Hydrologists from USGS Water Science Centers learn to operate the seismic equipment during technology demonstration and evaluation project.
During 2009, the Branch of Geophysics supported HVSR seismic technology demonstration and evaluation projects by USGS Water Science Centers (WSC) in locations around the Nation, including:
As part of the technology demonstration and evaluation, the Branch of Geophysics provided training to the USGS WSC hydrologists on data collection, processing, and interpretation. Each participating WSC had use of HVSR seismic equipment systems for 30 days to collect data to support an existing WSC project or program. In addition to providing technology transfer to the WSCs about this method and equipment, these pilot studies provided an evaluation of how and in what hydrogeologic settings HVSR seismic surveys can best be used to support development of USGS groundwater flow models.
The HVSR (also known as H/V for "horizontal-to-vertical") method uses a single, broad-band three-component seismometer to record ambient seismic noise. It is considered a "passive" seismic method because it does not require an artificial seismic source, such as an explosive charge or hammer blow. The HVSR method measures vertical and two horizontal (north-south and east-west) components of ambient seismic noise, which includes microtremors induced by wind, ocean waves, and anthropogenic activity. The ratio of the averaged horizontal-to-vertical frequency spectrum is used to determine the fundamental site resonance frequency, which can be interpreted using regression equations to estimate sediment thickness and depth to bedrock.
A broadband, three-component seismometer.
For more information about applied research on the use of HVSR seismic methods in groundwater investigations, contact John W. Lane, Jr., Chief, Branch of Geophysics or see the publications listed below.
This project was conducted with support from the USGS Groundwater Resources Program.
Lane, J.W., Jr., White, E.A., Steele, G.V., and Cannia, J.C., 2008, Estimation of bedrock depth using the horizontal-to-vertical (H/V) ambient-noise seismic method, in Symposium on the Application of Geophysics to Engineering and Environmental Problems, April 6-10, 2008, Philadelphia, Pennsylvania, Proceedings: Denver, Colorado, Environmental and Engineering Geophysical Society, 13 p.
Lane, J.W., Jr.; Liu, Lanbo; Chen, Yongping; and White, E.A., 2007, Near-surface site characterization using a combination of active and passive seismic arrays: EOS Transactions, American Geophysical Union, v. 88, no. 52, Fall Meeting Supplement, Abstract H13M-04.
Liu, Lanbo; Zhu, Lieyuan; and Lane, J.W., Jr., 2007, Analysis of the two-dimensional effect in the H/V spectral ratio method for bedrock depth estimation on bedrock depth estimation by the H/V seismic method [abs]: EOS Transactions, American Geophysical Union, v. 88, no. 52, Fall Meeting Supplement, Abstract H21A-0187.
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