Non-linear crustal corrections in high-resolution regional waveform seismic tomography
Non-linear crustal corrections in high-resolution regional waveform seismic tomography
复制标题
高分辨率区域波形地震层析成像中的非线性地壳校正
DOI：
10.1111/j.1365-246x.2007.03399.x
复制
发表时间：
2007
影响因子：
2.8
通讯作者：
B. Romanowicz
中科院分区：
文献类型：
--
作者：
F. Marone;B. Romanowicz
在非线性渐近耦合理论（NACT）的框架下，采用标准和改进的地壳修正，对长周期三分量基波和高模态地表波形数据进行了对比，得到了北美大陆下的三维上地幔各向异性结构。我们在高分辨率区域波形层析模型中修正地壳结构的改进方法超越了线性摄动近似，因此更准确地解释了观测到的短距离内莫霍地形的大变化，例如在海洋-大陆边缘。该改进方法将浅层校正分解为线性和非线性两个部分，利用根据局部构造构造定义的一维灵敏度核进行正演计算和反演灵敏度核计算。采用标准和改进的地壳校正方法得到的三维上地幔各向异性结构的对比表明，模型范数没有受到强烈的影响。然而，在检索到的三维扰动中观察到显著的变化。速度模型的最大差异出现在250公里深度以下，而不是像预期的那样出现在最上层地幔。我们建议，不准确的地壳修正优先映射到模型中约束最小的部分，因此，对浅层结构的准确修正对于提高我们对上地幔部分的认识至关重要，因为我们的数据具有最小的敏感性。
SUMMARY We compare 3-D upper mantle anisotropic structures beneath the North American continent obtained using standard and improved crustal corrections in the framework of Non-linear Asymptotic Coupling Theory (NACT) applied to long period three component fundamental and higher mode surface waveform data. Our improved approach to correct for crustal structure in high-resolution regional waveform tomographic models goes beyond the linear perturbation approximation, and is therefore more accurate in accounting for large variations in Moho topography within short distances as observed, for instance, at ocean‐continent margins. This improved methodology decomposes the shallow-layer correction into a linear and non-linear part and makes use of 1-D sensitivity kernels defined according to local tectonic structure, both for the forward computation and for the computation of sensitivity kernels for inversion. The comparison of the 3-D upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected. However, significant variations are observed in the retrieved 3-D perturbations. The largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle, as would be expected. We suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow-layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity.