The seismic response of two-dimensional sedimentary deposits with large vertical velocity gradients
The seismic response of two-dimensional sedimentary deposits with large vertical velocity gradients
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发表时间：
1986-04
影响因子：
3
通讯作者：
P. Bard;J. Gariel
中科院分区：
文献类型：
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作者：
P. Bard;J. Gariel
Aki-Larner技术的延伸垂直不均匀介质，使垂直速度梯度可以考虑在二维模型。本文只考虑了SH波，但该理论对P波和SV波同样适用。应用该方法研究了具有大速度梯度的二维沉积层的地震响应。考虑三种不同的情况：浅的高对比度谷、深的高对比度谷和深的低对比度谷。在每种情况下，进行比较的结果，二维模型考虑到均匀的沉积物和一维模型考虑到沉积物的垂直不均匀性。大的速度梯度的存在不会改变很多的定性行为的二维存款：局部表面波和/或二维共振模式的情况下，均匀的沉积物观察。然而，表面波具有更低的相速度和群速度以及更大的振幅。只有非常深的山谷才会引起二维共振的发展。另一方面，在这样的存款中获得的放大可能会达到更大的值比那些预测的二维，均匀的模型或一维，不均匀的模型。由于这些结果已经获得了现实价值的山谷几何和力学的考虑，他们应该找到一些应用在地震工程或地震小区划研究。
An extension of the Aki-Larner technique to vertically inhomogeneous media is presented, so that vertical velocity gradients may be taken into account in two-dimensional models. Only SH waves are considered here, but the theory is valid for P and SV waves as well. This method is applied to investigate the seismic response of two-dimensional sedimentary deposits with large velocity gradients. Three different cases are considered: a shallow, high-contrast valley, a deep, high-contrast valley, and a deep, low-contrast valley. In each case, a comparison is performed with the results of a two-dimensional model taking into account only homogeneous sediments and a one-dimensional model taking into account the vertical inhomogeneity of sediments. The presence of a large velocity gradient does not change a lot the qualitative behavior of a two-dimensional deposit: local surface waves and/or two-dimensional resonance patterns are observed as in the case of homogeneous sediments. Nevertheless, the surface waves are much more dispersive with lower phase and group velocities and larger amplitudes. Only very deep valleys give rise to the development of two-dimensional resonance. On the other hand, the amplifications obtained in such deposits may reach much larger values than those predicted with either two-dimensional, homogeneous models or one-dimensional, inhomogeneous models. Since these results have been obtained for realistic values of valley geometrical and mechanical considerations, they should find some application in earthquake engineering or seismic microzonation studies.