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Journal: |
Earthquake Research In China 2009 No.3
clicks:823 |
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Title:
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Author:
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Liu Baojin Yang Xiaoping Feng Shaoying and Kou Kunpeng |
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Adress: |
Geophysical Prospecting Center ,China Earthquake Administration ,Zhengzhou 450002 ,China |
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Abstract:
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The great MS810 Wenchuan earthquake on May 12 ,2008 was generated by abrupt faulting in the Yingxiu2Beichuan fault along the Longmenshan fault zone. The earthquake not only produced surface ruptures along the Yingxiu2Beichuan and Guanxian2Jiangyou faults ,but also surface ruptures ,arching of highway pavement , sand2boils and waterspouts in various degrees in areas such as Shifang and Mianzhu on the Chengdu Plain. To understand the shallow geological structures under the surface rupture zone , a 6350m long high2resolution shallow seismic reflection prof ile in near2EW direction was performed. This prof ile is located at Shigu town ,Shifang city ,where a suspected earthquake surface rupture zone was discovered. In this
study ,a group interval of 3m ,shotpoint interval of 18m ,and a 3002channel 252fold observation system were used. In consideration of both near2surface reflections and dipping interface imaging , we adopted the split2spread geometry and asymmetrical zero2offset receiving technique. To better suppress random2noise and raise the signal2to2noise ratio of seismic data , 30 times vertical stacking of vibrator signals was made for each common2shot gather after correlation of individual records. By using the above work method and spread geometry , we obtained high2resolution images of structures in the depth range of 15m～ 800m after data processing. The result shows the existence of buried thrust faults thrusting to the plain area and back2thrust faults under the surface rupture zone. It also shows that the activity of the buried thrust faults may be the main cause for folding and deformation in near2surface strata and coseismic surface rupturing. |
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