Shear-wave anisotropy of the upper and lower crusts estimated by stripping analysis of Ps-converted waves
Shear-wave anisotropy of the upper and lower crusts estimated by stripping analysis of Ps-converted waves
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DOI：
10.1016/j.tecto.2015.07.016
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发表时间：
2015-09
期刊：
影响因子：
2.9
通讯作者：
M. Watanabe;H. Oda
中科院分区：
文献类型：
--
作者：
M. Watanabe;H. Oda
通过测量在康拉德和莫霍面转换的Ps相位的剪切波偏振各向异性，研究了地壳的各向异性结构。PS转换的相位上的P波接收器功能，这是从F-net和Hi-net站在近畿，中国，四国和九州地区在日本西南部的地震记录。通过各向异性层行进的Ps相经历剪切波分裂，其由分裂参数[快偏振方向（FPD）和分裂时间]描述。上、下地壳各向异性分别由Conrad和Moho Ps相的分裂参数估计，分裂参数由波形互相关法确定。为了可靠地估计下地壳各向异性，莫霍面Ps相位通过剥离法针对上地壳中的剪切波分裂效应进行校正，因为上地壳各向异性掩盖了下地壳中Ps相位的各向异性行为。上地壳和下地壳的裂分时间均小于0.2s，但它们的FPD特征各不相同。上地壳中的FPD主要为东西向。在菲律宾海板块俯冲区，下地壳的板块俯冲范围为NW-SE-NE-SW，而在非板块俯冲区，下地壳的板块俯冲范围为NE-SW-SE-NW。因此，地震各向异性存在于下地壳和上地壳，板片俯冲显著影响下地壳各向异性。上地壳各向异性最可能的原因是构造应力在上地壳中诱发的垂直裂缝的排列，而下地壳各向异性则归因于造岩矿物的晶格择优取向沿着下地壳的韧性变形。
The anisotropic structure of the crust is investigated by measuring the shear-wave polarization anisotropy of the Ps phases converted at the Conrad and Moho discontinuities. The Ps-converted phases are identified on the P-wave receiver functions, which are constructed from teleseismic records at the F-net and Hi-net stations in the Kinki, Chugoku, Shikoku, and Kyushu districts in southwest Japan. The Ps phase traveling through an anisotropic layer undergoes shear-wave splitting, which is described by splitting parameters [fast polarization direction (FPD) and split time]. The upper and lower crustal anisotropies are estimated from the splitting parameters of the Conrad and Moho Ps phases, respectively, which are determined by a waveform cross-correlation method. To reliably estimate the lower crustal anisotropy, the Moho Ps phase is corrected for the shear-wave splitting effect in the upper crust by a stripping method because the upper crustal anisotropy masks the anisotropic behavior of the Ps phase in the lower crust. The split times estimated for the upper and lower crusts are less than 0.2 s, but their FPD characteristics differ from each other. The FPDs in the upper crust are predominantly in the E–W direction. The FPDs in the lower crust range from NW–SE to NE–SW in the region with the Philippine Sea (PHS) slab subduction, but from NE–SW to SE–NW in the region without slab subduction. Thus, seismic anisotropy exists in both the lower and upper crusts, and slab subduction significantly influences the lower crustal anisotropy. The most likely cause for the upper crustal anisotropy is the alignment of vertical cracks induced in the upper crust by the tectonic stress, while the lower crustal anisotropy is attributed to the lattice preferred orientation of rock-forming minerals along with ductile deformation of the lower crust.