Abstract
AbstractA large shallow crustal earthquake occurred at the western off-shore of Fukuoka Prefecture, northern Kyushu, Japan, at 10:53 on March 20, 2005 (JST). Source rupture processes of the mainshock and the largest aftershock on April 20, 2005, are estimated by the kinematic waveform inversion of strong motion seismograms. The rupture of the mainshock started with relatively small slip, and the largest slip was observed at the southeast of the hypocenter. The inverted source models showed that both of the ruptures of the mainshock and the largest aftershock mainly propagated to southeast from the hypocenters, and the rupture area of those events did not overlap each other. Three-dimensional ground motion simulation by the finite difference method considering three-dimensional bedrock structure was also conducted to see the spatial variation of the near-source ground motion of the mainshock. The result of the simulation shows that expected groud motions are relatively large in and arround Genkai Island, Shikanoshima Island, and the center of Fukuoka City compared to the other area because of the rupture heterogeneity and the deep basin structure in Fukuoka City.
Highlights
At 10:53 on March 20, 2005 (JST), a large shallow crustal earthquake (MJMA 7.0) occurred beneath the Sea of Genkai, western off-shore of Fukuoka Prefecture, northern Kyushu, Japan
Three-dimensional ground motion simulation by the finite difference method considering three-dimensional bedrock structure was conducted to see the spatial variation of the near-source ground motion of the mainshock
Though this earthquake occurred beneath the sea, it brought severe strong ground motions to the nearsource region, such as Genkai Island, Shikanoshima Island, and the central district of Fukuoka City
Summary
At 10:53 on March 20, 2005 (JST), a large shallow crustal earthquake (MJMA 7.0) occurred beneath the Sea of Genkai, western off-shore of Fukuoka Prefecture, northern Kyushu, Japan. The source rupture process of the mainshock is estimated by the kinematic linear waveform inversion with multiple time windows (Sekiguchi et al, 2000). This methodology is originally based on the technique developed by Hartzell and Heaton (1983). To calculate the Green’s functions, a one-dimensional underground structure model is assumed for each station referring to the underground structure model proposed by Nakamichi and Kawase (2002) They used the underground structure model to evaluate the strong ground motions for a scenario earthquake on the Kego fault in Fukuoka City, so we think this model would be appropriate for the studied area in this paper. The rupture front propagation velocity, which triggers the rupture of the first time
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