A Novel Application of Earthquake Horizontal-to-Vertical Spectral Ratio

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Ground response analyses (GRA) model the vertical propagation of SH waves through flat-layered media (1DSH) and are widely carried out to evaluate local site effects. In contrast, horizontal-to-vertical spectral ratio (HVSR) technique is a cost-effective approach to obtain certain site-specific information, e.g., site resonant frequency but not the level of amplification. However, Kawase et al. (2019) proposed to double correct the noise HVSR and then use the corrected HVSR to directly estimate the S-wave amplification estimation. In this investigation, we develop a similar procedure to correct earthquake HVSR, which, in essence, compensates HVSR by generic vertical amplifications. Then we evaluate the effectiveness of the corrected HVSR in approximating observed amplification in comparison with that of 1DSH modelling. For this purpose, a total of 207 KiK-net surface-downhole recordings sites are analyzed, and 90 sites are found to have no velocity contrasts below downhole sensor and thus are utilized in the comparison. Empirical transfer function (ETF), derived from surface-to-borehole spectral ratio (SBSR) is taken as observed amplification. 1DSH-based theoretical transfer function (TFF) is computed in the linear domain considering the uncertainty in VS profile through Monte Carlo simulations. Five goodness-of-fit metrics are used to gauge the closeness between observed (ETF) and predicted (i.e., TTF and corrected HVSR) amplifications in both amplitude and spectral shape. Our preliminary results show that the empirical correction procedure to HVSR is highly effective and the corrected HVSR has a “good match” in both spectral shape (Pearson’s r > 0.6) and amplitude (Index of agreement d > 0.6) at 74% of the investigated sites, as opposed to 17% for 1DSH modelling. In addition, the HVSR-based empirical correction approach does not need a site model and thus has great potentials in site-specific seismic hazard assessments.

Presenting Author: Chuanbin Zhu

Authors