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Estimation of the Horizontal Site Amplification Factors at Sites in the Noto-hanto Area in Japan based on the Microtremor Horizontal-to-vertical Spectral Ratios: A Special Case for the Vertical Amplification Correction Function

Description: 

We have been studying the relationship between the Horizontal-to-Vertical Spectral Ratios of microtremors (mHVSRs) and the Horizontal-to-Vertical Spectral Ratios of earthquakes (eHVSRs), as well as the relationship between eHVSRs and the Horizontal Site Amplification Factors (HSAFs) of earthquakes delineated by the Generalized Inversion Technique (GIT, Nakano et al. BSSA2015). We proposed that we can transform mHVSR into pseudo eHVSR based on the empirically-obtained Earthquake-to-Microtremor Ratio (EMR). We also proposed the Vertical Amplification Correction Function (VACF) that can transform eHVSR or pseudo eHVSR into HSAF as the average of the Vertical Site Amplification Factor (VSAF*). We have proven that these double-correction method of EMR*VACF can successfully reproduce pseudo HSAF from mHVSR (Kawase et al., SDEE2018, Ito et al., BSSA2020).

Immediately after the Noto-Hanto earthquake of Mw7.4 that occurred on January 1, 2024, on a thrust fault of 150 km long extending in the northern part of the Noto Peninsula in Japan, we visited the heavily damaged cities and towns in the epicentral area to measure microtremors in order to delineate the site amplification factors and subsequent underground structures. We deployed our instruments at about 20 sites in Suzu City, Wajima City, Anamizu Town, and Nanao City. We collocated at least one site in each city and town with the strong-motion observation sites by NIED or JMA in order to verify the HSAF evaluation method by referencing HSAFs separated by GIT. At several sites with ordinary HSAFs we have successfully reproduced them by using the double correction method of EMR and VACF from mHVSRs. However, at three sites, namely ISK002, E10, and ISK005 with extraordinarily large (80~100 times) HSAFs in the frequency range equal to or less than 1 Hz, we found that we cannot reproduce observed HSAFs from pseudo eHVSRs unless we use VSAF* specific at these sites. This strongly suggests that the extraordinarily large HSAF and VSAF* at these sites could be the result of the 2D/3D deep basin resonances.

Session: Challenges and Opportunities in Constraining Ground-motion Models from Physics-based Ground-motion Simulations [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Eri

Student Presenter: No

Invited Presentation: 

Poster Number: 40

Authors