Rupture of Ramp-Décollement Faults in the 2008 Wenchuan Earthquake-Geodetic Evidence for the Uplift of the Longmenshan Driven by Convergent Deformation
详细信息
- 责任者：Tan Kai (Key Laboratory of Earthquake Geodesy ; Institute of Seismology ; CEA ; Wuhan 430071 ; China) ; Yang Shaomin
- 刊名：Chinese Journal of Geophysics
- 出版年：2013
- 卷期：56(5)
- 关键词：隆起 ; uplifts ; 滑脱断层 ; detachment faults ; 四川 ; Sichuan Province
- 页码：p.1506-1516
- 图表：illus., 1 table, 34 refs.
- 分类号：0300
- issnNo：ISSN0001-5733
- isbnNo：CN11-2074/P
摘要
The mechanism for the build-up of the Longmen Shan on the eastern margin of Tibet is controversial with two end-member models of crustal thickening -mid-crustal channel flow vs crustal shortening.The former states that the uplift of the Longmen Shan results from an eastward flowing of mid-lower crust from the interior of the Tibetan Plateau driven by the collision between India and Tibet.As a result,the thrust fault system on the foothill of the Longmen Shan was produced to accommodate differential vertical motions between eastern Tibet and Sichuan Basin,requiring no large-scale ramp-décollement structure associated with crustal shortening.In this study,we use dense near-field geodetic measurements of coseismic deformation to constrain rupture geometry and slip distribution of the Wenchuan earthquake.Our modelling shows a sub-horizontal décollement fault at depths of 16~21 km with a 60~80 km downdip width,on which there are several high-slip patches with peak values of 6~7 meters,altogether corresponding to 12% of total scalar geodetic moment.Deep slip with a dipping angle of 7° extends updip with rupturing on two high-angle ramp faults,one of which emerges at the surface as the Beichuan fault dipping about 55° to west.The great rupture on the ramp and décollement faults under the Longmen Shan provide evidence of the existence of a large-scale faulting system characterized with substantial crustal shearing at depth along a transition zone located between the upper brittle and the underlying ductile layers,suggesting that the crustal shortening across the eastern margin of the Tibetan Plateau gives rise to the growth of the Longmen Shan.
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