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A Gross Picture of the S-Wave Site Amplification Factors Throughout Japan Based on the Generalized Spectral Inversion and One-Dimensional Theoretical Prediction

Session: Data Fusion and Uncertainty Quantification in Shallow Crust Characterization and Modeling

Type: Oral

Date: 4/19/2021

Presentation Time: 06:00 PM Pacific

Description: 

We have been applying the generalized spectral inversion to strong-motion data in Japan (Nakano et al., 2015) in order to separate source, path, and site terms in the frequency range from 0.12 Hz to 15 Hz. We first focus our attention on the spatial distribution of the horizontal site amplification factors (HSAFs) of the S-wave part (5 to 15 s from the onset of S-wave). We have been using various kinds of site proxies to represent HSAFs empirically, however, we should see their spatial distribution before delineating the phenomenological correlations for these proxies. Thus, we plot a gross picture of the separated HSAF throughout Japan using GMT (Wessel and Smith, 1998) for 2600 sites of K-NET and KiK-net by NIED, JMA networks, and CEORKA network. The observed HSAF from the generalized inversion is the site amplification relative to the seismological bedrock with the S-wave velocity of 3.45 km/s. The gross picture of the observed HSAFs clearly shows that large sedimentary basins such as the Kanto, Osaka, Nobi, Sapporo, and Kumamoto basins are creating large amplifications. Amplifications in eastern Japan tend to be higher than those in the west.

A deep velocity structure from the engineering bedrock to the seismological bedrock throughout Japan, called JIVSM (Koketsu et al., 2012), was constructed to calculate theoretical long-period responses for selected scenarios of mega-thrust earthquakes along the Philippine-Sea Plate as a part of the activities in the National Headquarter of Earthquake Research Promotion. For shallow structures, we can use PS logging information published by NIED for K-NET and KiK-net. By combining these two structures directly, we can construct a pointwise 1D velocity model at each site and calculate its theoretical HSAF at 1700 sites of K-NET and KiK-net. In the same manner, we plot the gross picture of the theoretical HSAFs all over Japan. We can see quite similar spatial characteristics of site amplification in the theoretical HSAFs, however, we found that their amplifications are systematically deficient in comparison to the observed ones.

Presenting Author: Hiroshi Kawase

Student Presenter: No

Authors