Source- and Site-Specific Earthquake Ground Motions

T Nagao,Y Fukushima

doi:10.48084/etasr.3612

Abstract

Seismic design is the preparation for earthquake ground motions considering the seismicity and seismic amplification properties of the ground at the target site. However, the effects of source, path, and site amplification characteristics are not sufficiently anticipated in seismic codes. Regarding the source and path characteristics, earthquakes that have the strongest influence on the target site should be considered specifically, and, concerning seismic amplification, the effects of not only a shallow subsurface but also a deep subsurface should be considered. This article takes the design spectra of Japanese highway bridges as an object and compares them with the spectra produced by a ground motion prediction equation and the source- and site-specific spectra evaluated using a state-of-the-art method. The results show that the spectra differ greatly. In this way, the necessity of the application of a state-of-the-art technique in the evaluation of source, path, and site amplification characteristics is demonstrated.

Highlights

Earthquake Ground Motion (EGM) is affected by source, path, and site characteristics
: source- and site-specific EGM : EGM with 1D amplification : EGM using a Ground Motion Prediction Equations (GMPEs) : EGM according to the Japanese Specifications for Highway Bridges (JSHB)
Regarding EGMs for YMG019, the EGM according to the JSHB is relatively small because the region coefficient is as low as 0.8, it still overestimates the EGM when compared with source- and site-specific EGM because the site amplification factor at YMG019 is small. 1DEGM underestimates EGM, and the EGM of a GMPE is generally consistent with source- and site-specific EGM

Summary

Introduction

Earthquake Ground Motion (EGM) is affected by source, path, and site characteristics. Regarding the first two characteristics, AASHTO design specifications for bridges [1] and NEHRP-recommended seismic provisions for buildings [2] apply site-specific hazard analyses to reflect the effects of source and path characteristics on EGMs. Eurocode 8 [3] classifies the seismicity of the site according to the surface wave magnitude of the associated earthquake, and design coefficients for EGMs are specified according to the seismicity of the site of interest. Regarding the site amplification characteristic, almost all the seismic codes and Ground Motion Prediction Equations (GMPEs) consider the amplification only in relation to a shallow subsurface. The JSHB and Japanese building codes classify ground conditions in accordance with the natural period of the shallow subsurface, from the ground surface down to the engineering bedrock. It has been observed that the effect of a deep subsurface should be considered [7,8,9,10] and an evaluation of the amplification of shallow subsurfaces alone greatly underestimates the amplification values at the relevant sites [9, 10]

Objectives

Results

Conclusion