The Longmen-Shan fault zone,at the eastern margin of the Tibetan Plateau,is one of the mostextensively studied areas in the world,yet the deformation model and earthquake-generating mechanismremain subjects of vigorous debate.We present the three-dimensional (3-D) velocity models determined usinga large volume of seismic data,together with the crustal stress and GPS data analysis,to investigate the nucleiof crustal deformation and seismotectonics along the reverse-thrust and strike-slip fault zone.It has beenobserved that anomalously low velocity,with low resistivity related to the Sichuan foreland basin,is in sharpcontrast to high-velocity and high-resistivity anomalies in the Songpan-Ganze block in the upper crust.Thetomographic models presented here reveal two crustal bodies with anomalously low velocity and highconductivity underneath the Longmen-Shan fault zone,separated into three contrasting segments by the twocrustal bodies.The two low-velocity and low-resistivity bodies have been interpreted as being associated withextrusion of either fluids or products of partial melting from the lower crust and/or the upper mantle fromTibet.This suggests strong variations in the rheological strength of the rock in the eastern margin of Tibet.This finding implies that coupling between these presumably fluid-bearing bodies and earthquake generationcould be extremely complex.
展开▼
