摘要
P and some S arrival times were picked from 80 earthquakes recorded by 51 seismographs deployed on a profile that followed the southern Tibetan highway during 1992 Sino French seismic experiment.We analysed the azimuthal and distance variations of P, PKP residuals and S P travel time residuals along the profile and their tectonic implication, and finally, we applied the ″ACH″ inversion scheme to calculate the velocity perturbation in the crust and upper mantle. The initial results from our study are: (1) the upper mantle velocity beneath Tibetan Plateau is lower than that of normal continents, the lowest mantle velocity is found beneath QiangTang block. The early PKP residuals in the north (north to Sangxiong) of the profile indicates a shallower Moho depth. (2) The abrupt increase of S P travel time residuals northward from Indus Tsangpo Suture (ITS) and the low velocity crust feature in this area from tomography inversion evidenced the existence of partial melting within the crust. (3) Karakorum Jiali Fault Zones (KJFZ) may be the southern branch of Banggong Nujiang Suture (BNS), the southern boundary of Qiangtang block. (4) The high velocity anomaly beneath north Himalaya revealed by tomography inversion may represents the the front of the underthrusting Indian lithosphere. The lower velocity anomaly beneath the center of the profile may reflect the physical state change related to high temperature.
P and some S arrival times were picked from 80 earthquakes recorded by 51 seismographs deployed on a profile that followed the southern Tibetan highway during 1992 Sino French seismic experiment.We analysed the azimuthal and distance variations of P, PKP residuals and S P travel time residuals along the profile and their tectonic implication, and finally, we applied the ″ACH″ inversion scheme to calculate the velocity perturbation in the crust and upper mantle. The initial results from our study are: (1) the upper mantle velocity beneath Tibetan Plateau is lower than that of normal continents, the lowest mantle velocity is found beneath QiangTang block. The early PKP residuals in the north (north to Sangxiong) of the profile indicates a shallower Moho depth. (2) The abrupt increase of S P travel time residuals northward from Indus Tsangpo Suture (ITS) and the low velocity crust feature in this area from tomography inversion evidenced the existence of partial melting within the crust. (3) Karakorum Jiali Fault Zones (KJFZ) may be the southern branch of Banggong Nujiang Suture (BNS), the southern boundary of Qiangtang block. (4) The high velocity anomaly beneath north Himalaya revealed by tomography inversion may represents the the front of the underthrusting Indian lithosphere. The lower velocity anomaly beneath the center of the profile may reflect the physical state change related to high temperature.
