Radiation from point sources in general anisotropic media
Radiation from point sources in general anisotropic media
复制标题
一般各向异性介质中点源的辐射
DOI：
10.1111/j.1365-246x.1993.tb00889.x
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发表时间：
1993
影响因子：
2.8
通讯作者：
D. Gajewski
中科院分区：
文献类型：
--
作者：
D. Gajewski
摘要介绍了一种计算任意各向异性介质慢度表面几何性质的方法。这使得我们可以利用所考虑的波的慢度表面的高斯曲率来计算一般各向异性介质中的点源的位移场。由于所使用的公式是基于高频渐近的，只要不遇到慢度曲面的抛物线点，该程序就能给出可靠的结果。给出并讨论了代表地壳和上地幔岩石模型的点源辐射模式。将各向异性模型中的点源辐射与平均各向同性模型中的点源辐射进行了比较，强调了两者之间的差异。各向异性要么是由定向裂缝(地壳岩石)引起的，要么是由定向橄榄石晶体(上地幔岩石)引起的。考虑到仅在裂纹材料(水或气体)的物理参数上不同的定向裂纹模型，得到了明显不同的辐射方向图。具有湿裂纹的模型在某些方向上表现出准S波能量的集中，而具有干裂纹的相应模型则没有观察到这种效应。爆炸产生的准S波辐射图是多叶的，湿裂纹模型比干裂纹模型表现出更多的波瓣。橄榄石中的单力辐射表现出类S波的强烈能量聚焦(波调谐)，然而，对于具有约10%优先取向的橄榄石的实际上地幔岩石成分，这种波调谐不那么明显。
SUMMARY A procedure to evaluate the geometrical properties of the slowness surface for arbitrary anisotropic media is presented. This allows us to use results for computing the displacement field from point sources in general anisotropic media utilizing the Gaussian curvature of the slowness surface of the considered waves. Since the formulae used are based on high frequency asymptotics the procedure gives reliable results as long as no parabolic points of the slowness surface are encountered. Radiation patterns of point sources for models representing rocks in the crust and upper mantle are presented and discussed. The radiation from point sources in anisotropic models is compared with the radiation from point sources in average isotropic models to emphasize the differences. Anisotropy is either caused by aligned cracks (crustal rocks) or by aligned olivine crystals (upper mantle rocks). Considering models of aligned cracks differing only in the physical parameters of the crack material (water or gas) significantly different radiation patterns are obtained. Models with wet cracks exhibit focusing of quasi S-wave energy for some directions whereas this effect is not observed for the corresponding model with dry cracks. The quasi S-wave radiation pattern from explosions are multilobed and the wet crack models exhibit more lobes than the dry crack models. The radiation of single forces in olivine shows strong energy focusing (wave tuning) of quasi S waves, however, for realistic compositions of upper mantle rocks with some 10 per cent of preferentially orientated olivine this wave tuning is less pronounced.