| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2006: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Toward more precise estimation of earthquake hazard maps, we developed a statistical (empirical) evaluation method of strong motion spectra considering regional variation of source, path, and site effects in the Tohoku region, Japan. The main results are as follows.
1. We compiled strong-motion database over the Tohoku region from DPRI K-NET, KiK-net, PARI, JMA type-87 and type-95 strong-motion network data.
2. We conducted spectral inversion analyses for both S-wave Fourier and response spectra for the identical dataset, and obtained source spectrum of each earthquake, Q-value of propagating path (inland and subduction zones, differently), and site amplification factor at each site. By drawing maps of the Brune's stress drop and frequency-dependent site amplifications, the followings tendencies are found :
(1)high-frequency source radiation strength is very high at east of Miyagi prefecture area.
(2)shallow inland earthquakes located near volcanoes show lower high frequency radiation strength. Inland earthquakes at the other area have stress drops similar to the shallow earthquakes occurred in subduction zones.
(3)site amplification factors around 0.2Hz are large at Japan-Sea side, probably due to the basin depth of west of Ohu mountains are deeper than the east area. Still, amplifications around 0.5-2Hz, which is very important ranges for the earthquake damage for low-rise building, are large not only in the west of Ohu mountains but in the east area, such as Sendai plain.
3. Based on the results of spectral inversion, we evaluated attenuation relations of PGA, PGV, response spectrum by modeling earthquake term as a function of moment magnitude and stress drop, and also modeled site amplification factor as a function of Vs30, averaged S-wave velocity from the ground surface to 30m-deep. The variance of earthquake term is largely decreased by adding stress drop as a parameter.
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