Horizontal-to-Vertical Seismic Ratio (HVSR) Passive-Seismic Data Collected in Select Subwatersheds and Arroyos Near Los Planes, Mexico May 2022 to August 2023

Between May 2022 and April 2023, 57 passive seismic measurements were collected in select subwatersheds and arroyos near Los Planes, Mexico. 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 ~0.3 to 40 Hertz (Hz). Common sources of ambient noise include ocean waves, large regional storms, and tectonics. A resonance frequency (f0) is induced in the sediments 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 the 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 collected adjacent to nearby wells with known depth to bedrock. The average Vs, estimated to be 330 meters per second, was used along with the measured resonance frequency to estimate depth to bedrock at locations where depth to rock was unknown. Twenty‑five of the 57 measurements were deemed unusable due to a combination of poor instrument coupling with loose surface sediments and high uncertainty associated with low‑quality data. HVSR measurements from the remaining 32 locations were of sufficient quality to obtain f0 values, and the range of inferred depth to bedrock values were 1.0 to 107.9 meters. The raw data and output plots from processing are provided in this data release.