**6. Conclusions**

In order to evaluate an equivalent 1D S-wave site amplification factor at an arbitrary point, we propose an empirical method of correction on to the theoretical site amplification factor calculated from the unified velocity model of NIED for the Kanto and Tokai regions where the shallower- and deeper parts of the velocity structure are combined. First, we check how well the current unified velocity model in Japan can reproduce horizontal site amplification factors derived from the observed strong motions in the form of the equivalent 1D S-wave theoretical transfer functions at the nearest grid of every 250 m. The observed site amplification factors were obtained by GIT relative to the reference spectra extracted as the outcrop motions on the seismological bedrock. To be consistent with these observed site amplification factors, the theoretical transfer functions are calculated relative to the outcrop motions (twice of the input) on the seismological bedrock. We find that at about one-half of the sites the calculated 1D amplification factors show more or less acceptable fit to the observed ones, however, they tend to underestimate the observed amplifications in general. Therefore, we propose a simple, empirical method to fill the gap between the observed site amplification factors and the calculated ones based on the frequency and amplitude modification

**137**

**Author details**

\*, Kenichi Nakano2

1 DPRI, Kyoto University, Kyoto, Japan

provided the original work is properly cited.

2 HAZAMA ANDO CORPORATION, Tsukuba, Japan

\*Address all correspondence to: ito@sere.dpri.kyoto-u.ac.jp

, Shigeki Senna3

The authors declare that they have no conflict of interest.

3 National Research Institute for Earth Science and Disaster Resilience, Tsukuba,

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Hiroshi Kawase1

Eri Ito1

Japan

*S-Wave Site Amplification Factors from Observed Ground Motions in Japan: Validation…*

ratios. Once we obtain these modification ratios at 546 observed sites, we can interpolate them in space to obtain the modification ratios at an arbitrary point. Validation examples show that our proposed method effectively predict better site amplifications than the direct substitute of theoretical amplification factors at a

In the future investigation, we will apply the proposed correction method to the sites where we have observed records of either earthquakes or microtremors but we do not include them in the delineation of the modification ratios in order to further

This study has used the strong-motion observation records from the K-NET and KiK-net of the National Research Institute for Earth Science and Disaster Resilience (doi: 10.17598/NIED.0004) as well as the seismic intensity (Shindokei) network of the Japan Meteorological Agency (https://www.jma.go.jp/jma/indexe. html, last accessed November 2020). A part of this study was supported by the Japan Society for the Promotion of Science (JSPS) Kakenhi Grant-in-Aid for Basic Research (B) Number 19H02405. Continuous support from Hanshin Consultants

*DOI: http://dx.doi.org/10.5772/intechopen.95478*

validate the effectiveness of the proposed method.

site without observed data.

**Acknowledgements**

Co., Ltd. is highly appreciated.

**Conflict of interest**

*S-Wave Site Amplification Factors from Observed Ground Motions in Japan: Validation… DOI: http://dx.doi.org/10.5772/intechopen.95478*

ratios. Once we obtain these modification ratios at 546 observed sites, we can interpolate them in space to obtain the modification ratios at an arbitrary point. Validation examples show that our proposed method effectively predict better site amplifications than the direct substitute of theoretical amplification factors at a site without observed data.

In the future investigation, we will apply the proposed correction method to the sites where we have observed records of either earthquakes or microtremors but we do not include them in the delineation of the modification ratios in order to further validate the effectiveness of the proposed method.
