龙门山断裂带深部构造变形的粘弹性模拟分析
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摘要
根据龙门山断裂带地区的构造特征,建立该地区二维有限元模型.在考虑到深部构造发生粘弹性蠕动的条件下,利用粘弹性接触的有限元方法模拟计算上、下地壳和上地幔的滑动情况.模拟结果表明,龙门山断裂带及周围是应力集中区域,且随着时间的推移应力集中程度加剧.模拟还表明龙门山断裂带断层深处滑动速率比地表的滑动速率大,平均为3倍左右.因此,在龙门山断裂带地表滑动速率较小的情况下,速率较大的断层深部物质在滑动过程中则会产生能量高度的积聚,当能量积累超过极限强度,断层产生滑动,从而引发了地震.
Based on regional tectonic characteristics of the Longmen Shan fault zone,a two-dimensional finite element model is established,and the contact viscoelastic finite element method is used to simulate slippage situation between the lower crust and upper mantle with considering the creep effects in the internal structure.The simulation results indicate that there are stress concentration areas in the Longmen Shan fault zone and the surrounded regions and the stress concentration strengthens with time.And the slip rate of the lower crust is larger than that in the upper crust,and generally,it reaches three times.Since smaller slip rate exists near the surface of the Longmen Shan fault zone,however,material of the lower crust,which has larger slip rate,can generate energy accumulation during sliding.Once the energy exceeds the ultimate strength,and the fault will slip,therefore an earthquake occurs.
Based on regional tectonic characteristics of the Longmen Shan fault zone,a two-dimensional finite element model is established,and the contact viscoelastic finite element method is used to simulate slippage situation between the lower crust and upper mantle with considering the creep effects in the internal structure.The simulation results indicate that there are stress concentration areas in the Longmen Shan fault zone and the surrounded regions and the stress concentration strengthens with time.And the slip rate of the lower crust is larger than that in the upper crust,and generally,it reaches three times.Since smaller slip rate exists near the surface of the Longmen Shan fault zone,however,material of the lower crust,which has larger slip rate,can generate energy accumulation during sliding.Once the energy exceeds the ultimate strength,and the fault will slip,therefore an earthquake occurs.
引文
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[11]杨挺青.粘弹性力学[M].武汉:华中理工大学出版社,1990.
[12]Potvin M J.Comparison of time-domain finite element modelling of viscoelastic structures using anefficient fractional Voigt-Kelvin model or prony series[D].Montreal:Mcgill University,2001.
[2]Densmore A L,Ellis M A,Li Y,et al.Active tectonics of the Beichuan and Pengguan faults at theeastern margin of the Tibetan Plateau[J].Tectonics,2007,26:TC4005.
[3]Burchfiel B C,Royden L H,vander Hilst R D,et al.A geological and geophysical context for theWenchuan earthquake of 12May 2008,Sichuan,Peoples Republic of China[J].GSA Today,2008,18(7):4-11.
[4]张培震.青藏高原东缘川西地区的现今构造变形、应变分配与深部动力过程[J].中国科学:D辑,2008,38(9):1041-1056.
[5]赵祎喆,吴忠良,蒋长胜,等.用地震资料估计的龙门山断裂深部形变及其对于汶川地震成因的意义[J].地质学报,2008,82(12):1778-1787.
[6]Chen Q F,Li L,Niu F L,et al.Large slip rate detected at the seismogenic zone of the 2008 MW 7.9Wenchuan earthquake[J].Earthquake Science,2011,24(1):101-106.
[7]白超英,秦保燕.深部剪切形变带对浅源地震的控制——立交模式有限元的模拟计算[J].西北地震学报,1990(01):1-11.
[8]朱守彪,张培震.2008年汶川Ms8.0地震发生过程的动力学机制研究[J].地球物理学报,2009,52(2):418-427.
[9]Godard V,Pik R,LavéJ,et al.Late cenozoic evolution of the central Longmen Shan,eastern Tibet:Insight from(U-Th)/He thermochronometry[J].Tectonics,2009,28(5):TC5009.
[10]朱守彪,石耀霖.青藏高原地形扩展力以及下地壳对上地壳的拖曳力的遗传有限单元法反演[J].北京大学学报:自然科学版,2005,41(2):225-234.
[11]杨挺青.粘弹性力学[M].武汉:华中理工大学出版社,1990.
[12]Potvin M J.Comparison of time-domain finite element modelling of viscoelastic structures using anefficient fractional Voigt-Kelvin model or prony series[D].Montreal:Mcgill University,2001.
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