| Budget Amount *help |
¥7,800,000 (Direct Cost: ¥7,800,000)
Fiscal Year 1997: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 1996: ¥4,700,000 (Direct Cost: ¥4,700,000)
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| Research Abstract |
A direct three-dimensional boundary element method is applied to evaluate seismic responses in three-dimensional sedimentary basin to estimate the amplification characteristics of the ground motions in the heavily damaged belt zone in Kobe City during the 1995 Hyogoken eathquake. We have applied a direct 3-D boundary element method to evaluate seismic waves in a 3-D sedimentary basin due to 1)plane waves, 2)point sources, and 3)Haskel type fault. We have utilized the Green's functions for an elastic half-space medium. The accuracy of the Green's functions was verified through comparison of the numerical results with those obtained by other methods.
Firstly, we considered the incidence of plane waves of the P,SH,and SV waves. The dispersion curves of the fundamental modes of the surface waves for the two layred model of these velocity structures are, shown. From frequency domain results we computed synthetic seismograms using the FFT algorithm. Those responses clearly show propagation of
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Love waves generated from edge of the sedimentary basin. Thef also show that the center of the basin is most amplified since Love waves as well as Rayleigh waves generated from edge of the sedimentary basin propagate toward the center of the basin, and though several sites near the edge show some amplification, the magnitude of amplification remains to be less about 1.3 times than theremaining sites.
Secondly, we calculated the seismic motion of the basin to a point source. It is seen that body waves, i.e., SH waves, first arrive at the sites and then Love waves generated from the basin edge propagate forward along the longitudinal direction and propagate backward reflected from the other basin edge. It is also seen that though the body waves decay with the increase of source-receiver distance, Love waves do not decay because the material property of the basin is assumed to be a perfect elastic medium.It seems that the effect of angle of inclination of medium interface on the surface responses is small.
Finally, we calculated the seismic motion of the basin to a Haskell type fault source. Numerical results show that ground motions of some restricted area near basin edge are most amplified and that it is qualitatively verified that the amplification chariacterstics of the ground motions in the heavily damaged belt zone in Kobe city. Less
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