State of knowledge and practice on single-station microtremor horizontal-to-vertical spectral ratio (mHVSR) analysis for seismic site response

Alan Yong

Submitted September 7, 2025, SCEC Contribution #14671, 2025 SCEC Annual Meeting Poster #TBD

The resonant frequencies (fp) produced by unconsolidated sediments overlying high velocity bedrock are often used as the basis for estimating the seismic site response function. The lowest fp in the spectrum is distinguished as the site resonance (or fundamental) frequency (f0), whereas the frequency with the highest amplitude is the site dominant frequency (fd). The fd may or may not correlate with the f0, as it is possible that a site may also yield several peaks at frequencies higher than that of f0.

Several analytical methods have been developed to estimate frequency dependent site response. Most methods are based on spectral analyses (e.g., standard spectral ratio techniques) and do not require supplementary data beyond earthquake recordings. Nevertheless, sufficient earthquake recordings are not always readily available for robust analyses. Other site-specific approaches (e.g., one-dimensional frequency domain linear or equivalent linear ground response analysis) require several downhole body- or surface-wave based measurements from in situ seismic recordings. This field data acquisition portion of site characterization can be cost-, as well as environmentally, prohibitive.

To address these challenges, the single-station microtremor (i.e., ambient noise) horizontal-to-vertical spectral ratio (mHVSR) analysis method is gaining traction as a stop gap when earthquake data is scarce. The mHVSR method, however, still lacks consensus towards standardized guidelines and commercial use. The greatest challenges to an international standardization of mHVSR acquisition and analysis are two-fold: (1) the underlying composition of the microtremor wavefield is site dependent, therefore the appropriate theoretical model for inversion is still strongly debated; and, (2) there are many factors and options involved in the data acquisition, processing, and interpretation stages that remain inconsistently applied (Molnar et al., 2022).

I present briefly an update of the historical development of the mHVSR technique and the physical basis of the mHVSR. I then propose preliminary recommendations for developing guidelines for mHVSR acquisition and analysis.

Molnar, S., Sirohey, A., Bard, P.-Y., Castellaro, S., Cornou, C., Cox, B., Guillier, B., Hassani, B., Kawase, H., Matsushima, S., Sánchez-Sesma, F. J., and Yong, A. (2022). A Review of the Microtremor Horizontal-to-Vertical Spectral Ratio (MHVSR) Method, J. of Seism., https://doi.org/10.1007/s10950-021-10062-9.

Key Words
site effects, peak frequencies, fundamental frequency, dominant frequency, single-station, eHVSR, mHVSR

Citation
Yong, A. (2025, 09). State of knowledge and practice on single-station microtremor horizontal-to-vertical spectral ratio (mHVSR) analysis for seismic site response. Poster Presentation at 2025 SCEC Annual Meeting.

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