Passive Seismic Horizontal-to-Vertical Spectral Ratio Measurements at Transportation Infrastructure Sites in New Hampshire, 2022

In 2022, the U.S. Geological Survey (USGS) in cooperation with the New Hampshire Department of Transportation (NHDOT) made 107 horizontal-to-vertical spectral ratio (HVSR) passive seismic geophysical measurements at four transportation infrastructure sites in New Hampshire to determine the benefits of HVSR as an enhancement to traditional geotechnical site characterizations performed by NHDOT. Typically, data are obtained from the subsurface during borings to characterize geotechnical properties but often borings are spaced hundreds of feet apart. Geotechnical site characterization guided by geophysical surveys (such as the HVSR method) between borings will help provide a more thorough characterization. By combining analysis of geophysical and boring data, transportation projects can produce a more comprehensive representation of geotechnical subsurface conditions than can be determined using conventional borings alone.

The HVSR method measures the resonance frequency (f0) induced by ambient seismic noise in unconsolidated sediments overlying bedrock when there is a substantial contrast in shear-wave acoustic impedance between the two layers (> 2:1). Spectral ratio analysis of the horizontal and vertical components of the seismic data is used to determine f0. Overburden thickness can be related to f0 with thicker overburden related to lower frequencies, and higher frequencies with thinner overburden. A three-component seismometer was used to measure the vertical and horizontal components of ambient seismic noise using the HVSR method. This data release contains raw HVSR data and measurement locations.