Crustal anisotropy in the eastern Himalayan syntaxis and adjacent areas
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摘要:
利用喜马拉雅东构造结及周边地区的48个宽频带地震台站记录的远震波形数据，通过Pms波分裂测量得到了295对地壳各向异性横波分裂参数，获得了研究区的地壳各向异性图像.喜马拉雅东构造结的快波偏振方向主要为NE-SW方向，周边地区的快波偏振方向呈现出绕东构造结顺时针旋转的趋势.Pms波分裂的慢波延迟时间范围为0.11~0.30 s，平均值为0.24 s.对比分析研究区内Pms波分裂、近震直达S波分裂和远震SKS波分裂的结果发现，上地壳各向异性对Pms波分裂影响有限，地壳各向异性主要来自于中下地壳矿物和熔体的定向排列；地壳各向异性对SKS波分裂影响较小，SKS波分裂主要反映了上地幔的各向异性特征；Pms波分裂的快波偏振方向与近震直达S波分裂和远震SKS波分裂的快波偏振方向表现出较好的一致性，并且与地表构造和变形特征具有较好的相关性，反映了喜马拉雅东构造结及周边地区的岩石圈变形可能为垂直连贯变形模式.
Abstract:This work is based on teleseismic waveform data of 48 broadband seismic stations in the eastern Himalayan syntaxis and adjacent areas. We acquired 295 pairs of anisotropy parameters by measurement to Pms wave splitting, which permit to image the crustal anisotropy of the study area. Results show that the fast wave polarization directions of the eastern Himalayan syntaxis are NE-SW, rotating clockwise in the adjacent areas. The delay time of the Pms wave splitting in the study area ranges from 0.11 s to 0.30 s, with an average of 0.24 s. Comparison of the Pms wave splitting, the direct S wave splitting and the teleseismic SKS wave splitting suggests that the crustal anisotropy of the eastern Himalayan syntaxis and adjacent areas is mainly from the middle and lower crust, and the Pms wave splitting mainly reflects the anisotropy of the middle and lower crust. It also shows that the crust anisotropy has little effect on the SKS wave splitting, and SKS wave splitting is attributed to the anisotropy of the upper mantle. The fast wave polarization directions of the Pms wave splitting are well consistent with those of the direct S wave splitting and the teleseismic SKS wave splitting, and have good correlations with surface structures and deformation characteristics, indicating that the lithospheric deformation of the eastern Himalayan syntaxis and adjacent areas can be characterized by a vertical coherent deformation model.
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图 5
喜马拉雅东构造结Pms波分裂各向异性结果
Figure 5.
The results of the Pms wave splitting in the eastern Himalayan syntaxis
图 6
各台站Pms波分裂结果随地震事件后方位角分布变化情况
Figure 6.
The results of the Pms wave splitting with different back azimuths of seismic events in each station
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