S wave splitting observed in southwest Japan
S wave splitting observed in southwest Japan
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日本西南部观测到 S 波分裂
DOI：
10.1016/s0040-1951(96)00205-3
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发表时间：
1997
期刊：
影响因子：
2.9
通讯作者：
H. Shimizu
中科院分区：
文献类型：
--
作者：
H. Oda;H. Shimizu
本文研究了日本西南部中国地区SBK地震台记录的S波和ScS波的横波偏振各向异性。用波形互相关法测量了被弹性各向异性分裂的剪切波快分量的偏振方向和时间滞后。S波和ScS波分裂的比较表明，在400 km深度以上的上地幔中，剪切波各向异性大于400 km深度以下的下地幔中，分裂的ScS波快分量几乎都是向北西-南东方向偏振的，与震中方位角无关。该极化方向与直达S波快分量的极化方向一致，但伊豆-小笠原弧区深震辐射的S波表现出与ScS波不同的NE-SW方向的极化各向异性。NW-SE偏振方向是由于菲律宾海板块俯冲到日本西南部引起的上地幔速度各向异性，NE-SW偏振方向是由于太平洋板块俯冲带伊豆-小笠原地区弧后地幔的各向异性。这种极化各向异性是由于大洋板块俯冲导致上地幔橄榄石晶体产生形变诱导晶格择优取向所致。
Shear wave polarization anisotropy was investigated for S and ScS waves recorded at seismological station SBK in the Chugoku district, southwest Japan. Polarization direction of the fast component and time lag of shear wave which was split by elastic anisotropy were measured by a waveform cross-correlation method. Comparison between splittings of the S and ScS waves reveals that the shear wave anisotropy is higher in the upper mantle above the depth of 400 km than in the lower mantle below it. The fast components of the split ScS waves were polarized nearly in the NW–SE direction, irrespective of azimuth angles of earthquake epicenters. This polarization direction agrees with that of the fast components of the direct S waves, but the S waves radiated from deep earthquakes in the Izu–Ogasawara arc region show the polarization anisotropy of the NE–SW direction which is different from that of ScS waves. The NW–SE polarization direction is attributed to the velocity anisotropy in the upper mantle caused by subduction of the Philippine Sea plate beneath southwest Japan and the NE–SW polarization direction is interpreted as being due to the anisotropy in the back arc mantle under the Izu–Ogasawara region which is a subduction zone of the Pacific plate. The measured polarization anisotropy is due to deformation-induced lattice preferred orientation which is caused to olivine crystals in the upper mantle by subduction of oceanic plate.