Crustal Structure Variation Across The Northern Yadong-Gulu Rift From Teleseismic Receiver Function Studies

The Yadong-Gulu rift is one of several long north-south oriented rifts iin southern Tibet formed as a result of the east-west extension of the Tibetan lithosphere. We investigated crustal structure variation across the rift north of the Yarlung-Zangpo Suture using available broadband seismic stations in the region. P receiver functions of 61 stations were calculated using teleseismic events larger than 5 since 1991. Crustal thicknesses and Vp/Vs ratios at individual stations were estimated using the H-kappa stacking technique. High resolution images of the crust and uppermost mantle across the rift were obtained using the Common Conversion Point (CCP) stacking method. Receiver functions and surface wave dispersion data derived from ambient noise cross-correlation were combined to determine 1-D S-wave velocity models beneath stations in and outside the rift. The results show a clear and relative Moho at about 70 km depth outside the rift zone. The crustal structure in the rift zone is more complicate. There are two strong interfaces at depths of 15 km and 50 km in addition to a weak Moho at 70 km depth. The rapid variation of lower crustal structure across the rift zone indicates that the rifting is not decoupled at the mid crust level and the whole southern Tibetan crust, probably the lithosphere too, is undergone rifting deformation at several narrow zones.