Principal Research Results

Investigation of Source, Path and Deep Local Site Effects for Evaluationof Broadband Strong Ground Motions
Background
It is necessary to precisely predict the seismic ground motions at the specified evaluation point for advanced seismic designof energy facilities such as nuclear power plants. Since the characteristic period is different according to the target structure, theevaluation of the strong motion in the period range from about 0.1 to 10 seconds is required. The quantitative modeling techniques ofseismic source, wave propagating path from source to site, and deep subsurface structure beneath the evaluation site are important toovercome such issues.

Objectives
The purpose of this study is to reveal the detailed source, path, and local site effect of the past earthquakes for the development of broadband strong-motion prediction method, along with the investigation of deep velocity profile particularly for the estimation of the long-period motions.

Principal Results
1. Spatio-temporal rupture process during the large destructive earthquake using the inversion
technique
Since the spatial distributions of slip and stress drop on the seismic fault affect the strong ground motions observed particularly in the near-source area, it is important to examine such detailed source rupture process for the evaluation of strong ground motion
from inland crustal earthquakes. In this study the source inversion technique is applied to the strong-motion records from the 2007
Niigata-ken Chuetsu-Oki earthquake of M 6.8, and the distribution of asperities, which are areas of relatively large slips, is specified(Fig.1 and 2).
2. Separation analysis of source and path effect from the strong-motion records for the intra-plateearthquakes
It has been difficult to determine the source parameters of intra-plate earthquakes particularly for the Philippine Sea Plate
due to a lack of data for historical large events. Here the spectral inversion analysis is carried out on the data containing the 2004 off
the Kii peninsula earthquakes, which are recognized as intra-plate events, to derive the source and the path effect separately. As aresult we find the relatively low attenuation effect (high Qs values) along the wave-propagation path in the Kii peninsula region(Fig.3). The high-frequency excitations during the 2004 off the Kii peninsula earthquake sequence correspond to the empirical
relationship derived from the database of crustal and inter-plate earthquakes (Fig.4).
3. Deep subsurface structure modeling for the evaluation of long-period ground motion
Exploration of deep S-wave structure is conducted to the Niigata plain where thick sedimentary layers raise large longperiod motions. Microtremor array observation reveals the basin structure along the north-south coast line with the thickest sedimentsof 5 km near Niigata city (Fig.5). The postdiction of the long-period spectral level from the 2007 Niigata-ken Chuetsu-Oki earthquake
shows the good agreement with the observed data by using the normal mode solution based on the estimated one dimensional deep Swave structure model (Fig.6).

Future Developments
The methodology of broadband strong-motion prediction reflected the knowledge obtained in this study will be constructed
and probabilistic approach such as seismic hazard analysis will be integrated to build the comprehensive strong-motion evaluation
system.
Main Researcher: Yoshiaki SHIBA, Ph. D. and Hiroaki Sato,Research Engineer, Earthquake Engineering Sector, Civil Engineering Research Laboratory
Reference
H.Sato, et al., 2007, “Exploration of deep S-wave velocity structure using microtremor array technique to estimate long-period groundmotion”, CRIEPI Report N07004 (in Japanese)
Y. Shiba, et al., 2007, “Source and path characteristics of earthquakes occurring off the Kii peninsula”, CRIEPI Report N07007 (inJapanese)1229. Construction and Preservation of Electric Facilities

Fig.2 Estimated slip distribution model of the2007 Niigata-ken Chuetsu-OkiearthquakeFig.1

Fault plane of the 2007 Niigata-ken
Chuetsu-Oki earthquake and strongmotion stations used in the source
inversion analysis (triangles) together
with the microtremor site (doublecircles)

Dan et al. (2001)

Fig.4

Kato (2004)

Relationship between the seismic
moment and the acceleration source
spectral level. Solid line shows theempirical scaling relation. Open andsolid circles indicate intra-plate andinter-plate earthquakes respectively.
2007 Off Chuetsu eq.
(M6.8, Depth12km)

2Fig.3 Comparison of the Qs values in the Kii
peninsula (circles and red broken line)with those estimated in other regions ofJapan (yellow colored area).
0Depth(km)1233.0km/s

MAKNIG

SEI

MRA

0.8km/s

0.7km/s

0.4km/s
0.8km/s

1.0km/s
2.0km/s
2.3km/s

1.4km/s

1.5km/s

0.3km/s

1.4km/s4

Calculated
level果スペクトルの評価結110

Observedける
spectra
NIGH05にお観測結果
NS

10

2.1km/s

3.0km/s

Fig.6

1.9km/s

3.0km/s

EW

010

2.1km/s

5Fig.5TRD
0.4km/s
1.0km/s
1.9km/s
2.3km/s

Fourier amplitude (gal*s)

103.0km/s

Deep S-wave velocity structures beneath theNiigata Plain. The seismic basement with S-wave
velocity higher than 3 km/s forms basinstructure.

1230Period(s)101Comparison of observed
acceleration spectra from the2007 Niigata-ken Chuetsu-Oki
earthquake with the spectrallevel (red line) estimated from thenormal mode solution based on
the deep S-wave velocity profile
at SEI shown in Fig. 5.

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