DOI: 10.17603/ds2-4ehv-c597
title: Microtremor measurements collected from permanent stations in and around California and Nevada between 2000 and 2025
title: in Microtremor Horizontal-to-Vertical Spectral Ratios (mHVSR) from Permanently Installed Broadband Seismometers

description: Microtremor-based horizontal-to-vertical spectral ratios (mHVSR) offer valuable insights into subsurface geology, primarily through resonant features such as frequency spectrum peaks, which can be useful for predicting site response. Typically derived from three-component broadband seismometers over relatively short observation periods (1-2 hrs), mHVSR is a cost-effective and time-efficient method of site characterization. This approach has been shown to correlate with site-specific ground motion characteristics, and recent studies suggest that mHVSR holds significant potential for improving ergodic ground motion models (GMMs). In this study we extract microtremor data from permanent stations across the Western region of the United States (e.g., California, Nevada, Utah) from the Incorporated Research Institution for Seismology (IRIS), which archives data from various data centers (e.g., NCEDC, SCEDC). Each mHVSR curve was uniformly processed using the Python library hvsrprocpy (Ornelas et al., 2024) following standard procedures, with the exception of anti-triggering (or window rejection) because this step was found not to significantly impact the mean results, which is discussed further in the README file. These data were compiled to supplement the Community Shear-Wave Velocity (VS) Profile Database (VSPDB; https://vspdb.org), and for use during the development and application of mHVSR-conditioned GMMs for California. Funding for this research was provided by the California Strong Motion Instrumentation Program (CSMIP) under contract #1023-018, for which we are sincerely grateful. Additionally, partial funding was provided by Pacific Gas and Electric (PG&E), and we also deeply appreciate their support. Finally, we would like to express our sincere gratitude to the HVSR working group for their valuable exchange of information and constructive feedback.
description: The objective of this study was to collect ambient ground motion data (i.e., microtremors) from permanently installed broadband seismometers in and around California for the purpose of developing mHVSR curves to enhance the Community Shear-Wave Velocity (VS)  Profile Database (VSPDB) (Kwak et al. 2021; Ahdi et al. 2018; https://vspdb.org). In total, data was downloaded from 1,194 stations across California and neighboring regions, including Nevada and Mexico. The majority of the selected stations exhibited a flat frequency bandwidth ranging from 0.0083 to 100 Hz (0.01 to 120 seconds), with sampling rates between 80 and 250 Hz. Detailed information regarding the data type, sensor specifications, and other station-related metadata are provided in the accompanying metadata files. We focused on data recorded over approximately 2-hour durations to ensure adequate time windows for averaging, which is essential for generating HVSR at lower frequencies. Additionally, we prioritized downloading data from stations on dates with minimal anthropogenic noise, selecting data from various times between 2000 and 2025. Following the completion of quality checks, the dataset contains mHVSR data for 1,127 stations. A detailed explanation of the quality check process is provided in the README file. These data are of particular interest because they can be used to support the development of ergodic GMMs conditioned on mHVSR, since the stations also record earthquake ground motions. While previous studies have used eHVSR as a parameter for GMM development (e.g., Kwak et al., 2017), mHVSR is attractive due to its greater availability, as it can be readily obtained, unlike eHVSR, which relies on the occurrence of earthquakes and instrumentation at the site of interest. Future GMMs which consider mHVSR have the potential to significantly enhance site response estimations in the United States, where HVSR is not typically incorporated in practice.