Direct inversion of surface wave dispersion for three-dimensional shallow crustal structure based on ray tracing: methodology and application
Direct inversion of surface wave dispersion for three-dimensional shallow crustal structure based on ray tracing: methodology and application
复制标题
基于射线追踪的三维浅地壳结构面波色散直接反演方法与应用
DOI：
10.1093/gji/ggv080
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发表时间：
2015-06-01
影响因子：
2.8
通讯作者：
van der Hilst, Robert D.
中科院分区：
文献类型：
--
作者：
Fang, Hongjian;Yao, Huajian;van der Hilst, Robert D.
我们提出了一种方法来反演面波频散数据直接为3-D变化的剪切波速度，也就是说，没有中间步骤的相位或群速度图，使用频率相关的射线追踪和基于小波的稀疏约束层析反演。快速推进法用于计算，在每个周期，面波旅行时和射线路径之间的源和接收器。这避免了在大多数表面波层析成像研究中使用的大圆传播假设，但这在复杂介质中是不合适的。为了简化问题，我们考虑具有平滑变化的地震属性的准分层艾德介质。我们通过网格点下的1-D轮廓表示3-D剪切波速度模型，这些轮廓是使用基于小波的稀疏约束层析成像方法同时从所有色散数据确定的。波速模型的小波系数采用迭代加权最小二乘算法进行估计，并在迭代时使用新获得的波速模型更新表面波射线路径和数据灵敏度矩阵。为了证明其可行性，我们应用该方法来确定3-D浅层地壳剪切波速度的变化，在台湾台北盆地使用短周期站间瑞利波相位速度频散测量提取的环境噪声互相关方法。结果与以往的研究结果一致，并揭示了强烈的浅层地壳的非均匀性，与地表地质。
We propose a method to invert surface wave dispersion data directly for 3-D variations of shear wave speed, that is, without the intermediate step of phase or group velocity maps, using frequency-dependent ray tracing and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. To simplify the problem we consider quasi-stratified media with smoothly varying seismic properties. We represent the 3-D shear wave speed model by means of 1-D profiles beneath grid points, which are determined from all dispersion data simultaneously using a wavelet-based sparsity-constrained tomographic method. The wavelet coefficients of the wave speed model are estimated with an iteratively reweighted least squares algorithm, and upon iteration the surface wave ray paths and the data sensitivity matrix are updated using the newly obtained wave speed model. To demonstrate its feasibility, we apply the method to determine the 3-D shallow crustal shear wave speed variations in the Taipei basin of Taiwan using short period interstation Rayleigh wave phase velocity dispersion measurements extracted from the ambient noise cross-correlation method. The results are consistent with previous studies and reveal strong shallow crustal heterogeneity that correlates with surface geology.