关键词: 汶川M_S 8.0地震, 地表破裂带, 浅层地震反射剖面, 隐伏逆断层

Abstract: The M_S 8.0 great Wenchuan earthquake of May 12th,2008 was generated by abrupt faulting of the Yingxiu-Beichuan Fault along the Longmenshan Fault zone.The earthquake produced not only the surface ruptures along the Yingxiu-Beichuan Fault and Guanxian-Jiangyou Fault,but also surface rupture,highway's pavement arching,sand-boils and waterspouts in various degrees in the areas such as Shifang and Mianzhu of the Chengdu plain.To know the shallow geological structures under the surface rupture zone,a high-resolution shallow seismic reflection profile of 6350m long in near-EW direction was completed.This profile is located at the Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered.In this study,a trace interval of 3m,shot interval of 18m,and a 300-channel 25-fold observation system was used.In order to give consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique.For suppressing random-noise and raising signal to noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records.By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15～800m after data processing.The result shows that there are the buried thrust fault thrusting to the plain and the back-thrust fault under surface rupture zone,and that the activity of the buried thrust fault may be the main causes for folding and deformation in near-surface strata and for the coseismic surface rupturing.

Key words: M_S 8.0 Wenchuan earthquake, surface rupture zone, shallow seismic reflection profile, buried thrust fault