Horizontal-to-Vertical Seismic Ratio (HVSR) Passive-Seismic Data Collected at the USGS Kankakee Research Site in Hanna Township Indiana July-August 2023

In July and August 2023, 11 passive seismic surveys were conducted at or near the U.S. Geological Survey Kankakee River Research Site in Hanna Township, Indiana. The horizontal-to-vertical spectral ratio (HVSR) method is a passive seismic technique that uses a three-component seismometer to measure the vertical and horizontal components of seismic noise in the range of ~0.1 to 50 Hertz (Hz). The ambient source of noise is caused by ocean waves, large regional storms, and tectonic sources. A resonance frequency (f0) is induced in the unconsolidated when there is a substantial contrast (greater than 2:1) in shear-wave acoustic impedance between the overburden and the bedrock. The f0 is determined from the analysis of the spectral ratio of the horizontal and vertical components of the seismic data. The thickness of the overburden can be related to the f0. In general, lower f0 relates to thicker sediments, and higher f0 relates to relatively thinner overburden. An estimate of the depth to the contact between the unconsolidated layer and top of bedrock can be computed using either a direct measurement of shear wave velocity (Vs) or an indirect measurement of Vs. For this data set, Vs was computed indirectly using four HVSR measurements taken adjacent to two nearby wells with known depth to bedrock at each well. The average Vs, which was estimated to be 226 meters per second, was used along with the measured resonance frequency to estimate the depth to bedrock at seven other locations where depth to rock was unknown. All HVSR measurements had sufficient quality to obtain f0 values and data and output plots are provided in this data set.