Shear wave anisotropy beneath the Qinghai and Tibetan Plateau
Danian, Shi; Yingjun, Dong; Mei, Jiang; Kaiyi, Ma; Poupinet, G.; Him, A.; Nercessian, A.
published: Jan 1, 1999
ArtNo. ESP136000701013, Price: 19.00 €
During the two years of Sino-French cooperative research program (1992-1993), total of 108 digital seismic stations were deployed in two phases along the profile from Tingri, the south of Tibet, to Xietiesam, the north of Qinghai province. Four months of field recording resulted in hundreds of teleseismic events. Obvious SKS and PKS splitting has been observed on the seismograms of the 43 three-component stations with more than one event. Measurements of the fast polarization and the delay time show a very big difference on the two sides of Indus-Tsangpo suture (ITS) but little difference on the elder Bangong-Nujiang suture (BNS) and Jinshariver suture (JS). Obvious inconsistency exists between the anisotropy directions and the superficial tectonic/geological trends, which might not be explicable directly by the coherent upper mantle deformation usually supposed in a collisional belt. On the other hand, however, strong spatial relationships were revealed by our anisotropy results, such as the perpendicular directions of anisotropy on both sides of ITS and the good correlation between the region of larger magnitude of anisotropy and the zone of inefficient Sn propagation of Qiangtang as well as the systematic rotation of its directions of anisotropy, which should testify much more complicated aspects of the continental convergence mechanism. To the best of our data, we tend to suppose that Qinghai-Tibet plateau might result from a mechanism complicated by the coexistence of Argand's underthrust and Dewey's diffuse deformation, and Qiangtang region might be most probably undergoing the delamination.