Microtremor measurements collected from permanent stations in and around California and Nevada between 2000 and 2025

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.