Seismic P-wave tomography in eastern Tibet: Formation of the rifts

Abstract

For better studying the relationship between the rifts and deep structure, a detailed P-wave velocity structure under eastern Tibet has been modeled using 4767 arrival times from 169 teleseismic events recorded by 51 portable stations. In horizontal slices through the model, a prominent low-velocity anomaly was detected under the rifts from the surface to a depth of ∼250 km; this extends to a depth of ∼400 km in the vertical slice. This low-velocity anomaly is interpreted as an upper mantle upwelling. The observations made provide seismic evidence for the formation of north-south trending rifts. East of the low-velocity anomaly, a clear high-velocity anomaly is found between depths of 40 and 200 km. Due to its shallow depth, we suggest that it consists of materials from an ancient continental closure rather than the Indian Plate. From depths of 250 to 400 km, a high-velocity anomaly appears to the south of the Jiali Fault. This anomaly may correspond to the northern edge of the Indian Plate that detached from the surface under the Himalayan block. We suggest that the Indian Plate underthrusts no further than the Jiali Fault in eastern Tibet.