Azimuthal variation in seismic anisotropy of the southern California uppermost mantle
Azimuthal variation in seismic anisotropy of the southern California uppermost mantle
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DOI：
10.1029/2001jb000637
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发表时间：
2003
影响因子：
--
通讯作者：
P. Davis
中科院分区：
文献类型：
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作者：
P. Davis
[1]Backus [1965]的地震各向异性理论被用来获得射线与斜方弹性张量的对称轴成小角度时的准P波和S波的速度和偏振的表达式。给出了P波偏振和S波分裂参数与入射角θ和方位角z的关系式。对于小θ，分裂和P波速度主要表现为两个z变化。P波速度的平方由vp 2 = v0 2 + c1θ2 + c2 cos（2 z）θ2给出，其中ci是弹性张量系数的组合。对应于快、慢S波的本征值由类似的表达式给出。P波水平极化的变化表现为2 z变化; δzp = −Δz sin（2 z），对θ的依赖性很小。SKKS和SKS分裂参数表现出由下式给出的方位角变化：δ t = δ t0 + d1 sin（2 z）θ2和δt = δt0 + e1θ2 + e2 cos（2 z）θ2，其中δ t是快方向，δt是时间延迟。我们报告在全球地震台网台站在南加州的分裂参数的2 z变化。我们使用地震各向异性的其他估计来反演弹性张量的深度平均值。所得到的张量充分描述了P波水平极化中的方位角变化[Schulte-Pelkum等人，2001]、Pn、Rayleigh和Love波速度以及SKKS和SKS分裂，表明它们都来自地幔上部200 km的各向异性的共同来源。
[1] The Backus [1965] theory of seismic anisotropy is used to obtain expressions for the velocities and polarizations of quasi-P and S waves for rays making small angles to the symmetry axes of an orthorhombic elastic tensor. Expressions are found for P wave polarization and S wave splitting parameters as a function of incidence angle θ and azimuth z. For small θ, splitting and P wave velocity exhibit predominantly a two z variation. P wave velocity squared is given by vp2 = v02 + c1θ2 + c2cos(2z)θ2, where the ci are combinations of coefficients of the elasticity tensor. The eigenvalues corresponding to the fast and slow S waves are given by similar expressions. Variation in P wave horizontal polarization exhibits a 2z variation; δzp = −Δz sin(2z) with little dependence on θ. SKKS and SKS splitting parameters exhibit an azimuthal variation given by ϕ = ϕ0 + d1 sin(2z) θ2 and δt = δt0 + e1θ2 + e2 cos(2z)θ2, where ϕ is the fast direction and δt is the time delay. We report 2z variation in splitting parameters at the Global Seismic Network stations in southern California. We use other estimates of seismic anisotropy to invert for depth-averaged values of the elasticity tensor. The resulting tensor adequately describes azimuthal variation in P wave horizontal polarization [Schulte-Pelkum et al., 2001], Pn, Rayleigh and Love wave velocities, as well as SKKS and SKS splitting, suggesting they all arise from a common source of anisotropy in the upper 200 km of the mantle.