Horizontal-to-Vertical Spectral Ratio Soundings and Depth-to-Bedrock Data for Geohydrology and Water Quality Investigation of the Unconsolidated Aquifers in the Enfield Creek Valley, Town of Enfield, Tompkins County, New York, April 2013 - August 2015

From April 2013 to August 2015, the U.S. Geological Survey, in cooperation with the Town of Enfield and the Tompkins County Planning Department, collected horizontal-to-vertical seismic soundings at 69 locations in the Enfield Creek valley to help determine thickness of the unconsolidated deposits and depth to bedrock.

The HVSR technique, commonly referred to as the passive-seismic method, is used to estimate the thickness of unconsolidated sediments and the depth to bedrock (Lane and others, 2008). The passive-seismic method uses a single, broad-band three-component (two horizontal and one vertical) seismometer to record ambient seismic noise. In areas that have a strong acoustic contrast between the bedrock and overlying sediments, the seismic noise induces resonance at frequencies that range from about 0.3 to 40 Hz. The ratio of the average horizontal-to-vertical spectrums produces a spectral-ratio curve with peaks at fundamental and higher-order resonance frequencies. The spectral ratio curve (the ratio of the averaged horizontal-to-vertical component spectrums) is used to determine the fundamental resonance frequency that can be used along with an average shear-wave velocity or a power-law regression equation to estimate sediment thickness and depth to bedrock (Lane and others, 2008; Brown and others, 2013; Chandler and others, 2014; and Johnson and Lane, 2016).

The HVSR data presented in this data release were collected at each site for 30 minutes using a Tromino Model TEP-3C1 three-component seismometer. The data were processed with Grilla 2012 version 6.21 software to 1) remove anthropogenic noise, 2) convert the time-domain data to frequency domain, 3) compute and plot the spectral ratio curve, and 4) determine the resonance frequency.

This data release presents the resonance frequency peaks identified from the HVSR measurements. Also presented are reported depth-to-bedrock data for wells located at or near HVSR data-collection sites in the Town of Enfield for use in comparison of HVSR forward model depths to reported well depths. Raw and processed HVSR data for each HVSR measurement are presented in the attached. The HVSR data-collection sites are designated by a county sequential numbering system (TMHVSR79, TMHVSR80, etc. where TM indicates Tompkins County).

References

Brown, C.J., Voytek, E.B., Lane, J.W., Jr., and Stone, J.R., 2013, Mapping bedrock surface contours using the horizontal-to-vertical spectral ratio (HVSR) method near the middle quarter area, Woodbury, Connecticut: U.S. Geological Survey Open-File Report 2013-1028, 4 p., available at http://pubs.usgs.gov/of/2013/1028.

Chandler, V. W., and Lively, R. S., 2014, Evaluation of the horizontal-to-vertical spectral ratio (HVSR) passive seismic method for estimating the thickness of Quaternary deposits in Minnesota and adjacent parts of Wisconsin: Minnesota Geological Survey Open File Report 14-01, 52 p.

Johnson, C. D. and Lane, J. W., 2016, Statistical comparison of methods for estimating sediment thickness from horizontal-to-vertical spectral ratio (HVSR) seismic methods: An example from Tylerville, Connecticut, USA, in Symposium on the Application of Geophysics to Engineering and Environmental Problems Proceedings: Denver, Colorado, Environmental and Engineering Geophysical Society, pp. 317-323. https://doi.org/10.4133/SAGEEP.29-057.

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 Proceedings: Denver, Colorado, Environmental and Engineering Geophysical Society, pp. 490-502. https://doi.org/10.4133/1.2963289.