Array analysis of two-dimensional variations in surface wave phase velocity and azimuthal anisotropy in the presence of multipathing interference
Array analysis of two-dimensional variations in surface wave phase velocity and azimuthal anisotropy in the presence of multipathing interference
复制标题
DOI：
10.1029/157gm06
复制
发表时间：
2013-03
期刊：
影响因子：
--
通讯作者：
D. Forsyth;Aibing Li
中科院分区：
文献类型：
--
作者：
D. Forsyth;Aibing Li
面波的多径传播在波形中引入了失真，这可能会影响相速的阵列测量。我们提出了一种横向和方位变化相速度的阵列分析方法，它将每一次地震的入射波场表示为两个干涉平面波的总和。这个简单的近似很好地模拟了在东太平洋海隆的熔融实验中记录的大多数地震在16到67 S的周期内的幅度和相位变化。速度的反演自动地降低了来自地震或用这个近似不能很好描述的周期的数据的重要性。反演中的每一次迭代包括两个阶段：模拟退火法反演以获得每个事件的最佳波参数描述，以及线性化反演速度和波参数的变化。在29 S周期，双平面波解表明，几乎每个信号都受到多路径的显著影响。两个平面波中较大的一个通常有一个明显的传播方位，它位于大圆周路径的几度之内。较小的波离散度较大，视方位角相差约13°，在29 S处。研究区瑞雷波相速度的横向和方位变化都很显著，尽管可以抵消方位各向异性与速度的快速和可能不切实际的横向变化。视方位各向异性达5~6%，快方向大致垂直于山脊。
Multipath propagation of surface waves introduces distortions in waveforms that can bias array measurements of phase velocities. We present a method for array analysis of laterally and azimuthally varying phase velocities that represents the incoming wavefield from each earthquake as the sum of two interfering plane waves. This simple approximation successfully represents the amplitude and phase variations for most earthquakes recorded in the MELT Experiment on the East Pacific Rise in the period range from 16 to 67 s. The inversion for velocities automatically reduces the importance of data from earthquakes or periods that are not described well by this approximation. Each iteration in the inversion involves two stages: a simulated annealing inversion for the best wave parameter description of each event, and a linearized inversion for velocities and changes in the wave parameters. At 29 s period, the two-plane-wave solutions indicate that nearly every signal is significantly affected by multipathing. The larger of the two plane waves typically has an apparent azimuth of propagation that is within a few degrees of the great circle path. The smaller wave is more scattered, differing in apparent azimuth from the larger wave by an average of about 13° at 29 s. Both lateral and azimuthal variations in Rayleigh wave phase velocity in the study area are significant, although it is possible to trade off azimuthal anisotropy with rapid and probably unrealistic lateral variations in velocity. Apparent azimuthal anisotropy reaches 5 to 6%, with the fast direction approximately perpendicular to the ridge.