IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Oral Presentation 2263
Seismic velocity and anisotropy structures of the collision zone in
Himalaya
Prof. Zhifeng Ding
Institute of Geophysics, CEA IASPEI of China IASPEI
Wulin Liao, Hong Zhang, Guiyin Li, Hui Wang
Himalayan area is the collision zone of the Indian and Eurasian continents. With the increasing seismic
observatory data, we can obtain more and more evidences of the collision processes. In this research,
the seismic velocity map and the anisotropy of the lithospheric structures were used to study the
collision features. The seismic arrivals of the regional and teleseismic events were collected and used to
inverse the seismic structure in mid of the Himalayan area. These data were from the recordings of the
permanent and portable seismic stations in and around the mid of Himalayan area during the past 15
years. The 3-D seismic structures in the research area were obtained by using the seismic tomography
method (Zhao D., 1992, 1993). The shear wave anisotropies were also studied by using the seismic
recordings from the portable seismic stations which were deployed in Himalayan area during 2000-
2004. The results of the seismic tomography obviously show the collision structures in Himalayan area.
The abnormal higher velocity zones can be traced from the southern part of Himalaya north to the mid
of Tibetan region, with the increased depth. The images of the cross sections from to the northern part
of the Plateau show the clear subduction and collision structures of the Indian plate and the Eurasian
plate. The Indian lithosphere seemed to be delaminated into two subducting layers. The Lower part of
Indian crust subducted below to the Moho of the south , which can be trace up to the Bangong-Nujiang
suture; and the mantle lithosphere of the Indian continent subduct to the deeper part of the upper
mantle beneath the southern. The shear wave splitting were observed in the 39 stations in Himalayan
area. The fast polarization directions from the splitted S waves were vary in different part of the
research area. The directions were NWW or NW in western part, and near NS in eastern part of the
Himalayan area. Both the tomography and anisotropy research described the complicated collision
structures in Himalayan area. The subduction mechanisms of the Indian plate were not alike along the
collision front. The Indian plate may subduct to the Eurasian plate at some places which are low velocity
and higher temperature in upper mantle.
Keywords: himalaya, collision, structures