SPATIAL CHARACTERISTICS AND VISUAL EVALUATION OF STRONG GROUND MOTION ON 3-D SEDIMENTARY BASINS WITH THE AID OF PARALLEL COMPUTING

采用直接三维边界元法评价三维沉积盆地地震反应，对1995年神户市小庙地震重灾区带地震动的放大特征进行了估计。本文应用直接三维边界元方法对平面波、点源和Haskel型断层等三维沉积盆地的地震波进行了评价。我们对弹性半空间介质使用了格林函数。通过与其他方法计算结果的比较，验证了格林函数的准确性。首先，我们考虑了P波、SH波和SV波的平面波入射。给出了这些速度结构的两层模型的表面波基模的频散曲线。从频域结果，我们使用FFT算法计算合成地震图。这些响应清楚地表明，沉积盆地边缘产生了更多的Love波。沉积盆地边缘产生的Love波和Rayleigh波向盆地中心传播，对盆地中心的放大最大，边缘附近的几个位置虽然有一定的放大，但其放大幅度仍小于其他位置的1.3倍左右。其次，计算了盆地到点源的地震运动。可以看出，体波即SH波首先到达站点，然后从盆地边缘产生的Love波沿纵向向前传播，从另一个盆地边缘反射后向后传播。从图中还可以看出，虽然体波随源-接收距离的增加而衰减，但由于假定盆地的物质性质为完美弹性介质，Love波不衰减。介质界面倾角对表面响应的影响较小。最后，将盆地的地震运动计算为一个Haskell型断源。数值计算结果表明，靠近盆地边缘的一些限定区域的地震动放大最大，并定性地验证了神户市重灾区带地震动的放大特征。少

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 … More 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