Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic data collected on the Cedar River floodplain near Cedar Rapids, Iowa, May 2025

In May 2025, Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic surveys were done by the U.S. Geological Survey (USGS) at 28 locations in three field sites on the Cedar River floodplain near Cedar Rapids, Iowa. The USGS collected these data to determine depth to bedrock as part of a cooperative project with the City of Cedar Rapids to analyze the Cedar River alluvial aquifer. HVSR is a passive seismic technique that uses a three-component seismometer to measure the vertical and horizontal components of ambient seismic noise. Seismic noise in the range of approximately 0.1 Hertz (Hz) to 1 Hz is caused by ocean waves, large regional storms, and tectonic sources. A resonance frequency (f0) is induced in the unconsolidated deposits 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. Data for these surveys were collected using a Tromino Blu seismometer (https://moho.world/en/tromino/) and processed using MOHO Grilla HVSR software (https://moho.world/en/moho/).

This data release includes raw data files recorded by the Tromino seismometer in binary '.trc' format, raw data files exported from Grilla in ASCII '.saf' format, image files in 'jpg' format with plots generated using Grilla processing software of the spectral ratio and component power spectra for each measurement, a comma-separated values (.csv) file with tabular data about location and data acquisition notes for each survey site, and a metadata file in Extensible Markup Language (.xml) format.