Crustal velocity structure beneath the eastern Tibetan Plateau derived from double-difference travel-time tomography
The eastern margin of the Tibetan Plateau is covered by dense faults,with actively destructive earthquakes,which makes it a natural laboratory to study lateral extrusion mechanism of Tibetan Plateau and deep seismogenic environment.In order to understand the role of the Longmenshan subblock and its western boundary,the Longriba fault zone(LRBF),in the uplift of eastern Tibetan Plateau,we use double-difference tomography to reveal the crustal velocity structure beneath the Sichuan Basin and eastern Tibetan Plateau based on the event waveforms with magnitude ≥3.0 recorded by 64 broadband seismic stations between Jan.2008 and Dec.2015.The results show that the Longmenshan subblock,sandwiched between the Longmenshan fault zone(LMSF)and the LRBF,has obvious low crustal velocity characteristics compared with the LMSF itself and the Sichuan Basin to the east.Considering the low-resistance and low-density structure,as well as lack of seismicity within this block,especially in the LRBF,we speculate that this block is"relatively soft"to hardly produce brittle earthquake.During the strong interaction between the eastern edge of the Tibetan Plateau and the western edge of the Yangtze Block,this block absorbs the accumulated strain energy caused by plate extrusion mainly through crustal shortening and thickening and surface uplift.According to the velocity contour changes,we infer that the LRBF steeply dips southeastward in the deep and cuts into the basement,which probably releases its strain energy mainly by strike-slip movement.In contrast,the LMSF has a lower inclination angle leading to crustal shortening mainly by thrusting.In addition,according to the joint constraints of multiple velocity structures in this study,electrical and gravity anomalies revealed by other studies,we speculate that the Xianshuihe and Anninghe fault zones are also inclined to the southeast with a relatively large inclination angle,both of which extend at least into the middle-lower crust.
Eastern margin of the Tibetan PlateauDouble-difference tomographyLongmenshan subblockLongriba fault zone
万方数据
维普
