Site Effects Evaluation

**119**

**Chapter 5**

**Abstract**

at sites without observed data.

**1. Introduction**

S-Wave Site Amplification Factors

from Observed Ground Motions

in Japan: Validation of Delineated

Velocity Structures and Proposal

*Eri Ito, Kenichi Nakano, Shigeki Senna and Hiroshi Kawase*

We first derived site amplification factors (SAFs) from the observed strong motions by the Japanese nationwide networks, namely, K-NET and KiK-net of National Institute of Earthquake Research and Disaster Resilience and Shindokei (Instrumental Seismic Intensity) Network of Japan Meteorological Agency by using the so-called generalized spectral inversion technique. We can use these SAFs for strong motion prediction at these observation sites, however, we need at least observed weak motion or microtremor data to quantify SAF at an arbitrary site. So we tested the capability of the current velocity models in Japan whether they can reproduce or not the observed SAFs at the nearest grid of every 250 m as the one-dimensional theoretical transfer functions (TTF). We found that at about one-half of the sites the calculated 1D TTFs show more or less acceptable fit to the observed SAFs, however, the TTFs tend to underestimate the observed SAFs in general. Therefore, we propose a simple, empirical method to fill the gap between the observed SAFs and the calculated TTFs. Validation examples show that our proposed method effectively predict better SAFs than the direct substitute of TTFs

**Keywords:** site effect, generalized spectral inversion, strong motion, theoretical

The quantitative strong motion prediction with a source- and site-specific scheme is very important for mitigation of earthquake disaster and seismic design of important structures. It is especially true in Japan where large mega-thrust earthquakes are expected to occur within the coming 30 years. That is why we have a couple of nation-wide strong-motion networks in which a considerable number of

There are several ways to simulate strong-motions as waveforms on the surface at a target site located at an arbitrary position. One is a theoretical Green's function method (TGF) in which wave generation at the source, propagation from the

transfer function, velocity structure, seismological bedrock

strong motion records have been accumulated since 1996 [1].

for Empirical Correction
