Crustal anisotropy in the eastern Himalayan syntaxis and adjacent areas

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.

Automated summary

This study is based on teleseismic waveform data from 48 broadband seismic stations in the eastern Himalayan syntaxis and adjacent areas. The results show that the crustal anisotropy in these regions is mainly attributed to the middle and lower crust, with the Pms wave splitting reflecting the anisotropy of the middle and lower crust. The anisotropy of the upper mantle is believed to be responsible for SKS wave splitting.