兰州盆地最大潜在地震变形数值模拟
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摘要
在分析兰州盆地及周边地震构造环境、深部地球物理特征及盆地结构构造特征的基础上,建立了马衔山北缘断层西段发震的三维地震构造模型。采用三维有限元方法计算了该断层段未来发生MS7.0地震在兰州盆地的变形影响。计算结果表明:地震产生的变形及地震应力在兰州盆地区内已有很大程度的衰减,在量值上从盆地西侧到盆地东侧总位移值从1.25 m降至0.3 m;盆地内部最大地震应力则基本保持在0.02 MPa左右,只在盆地边缘及高阶地前缘局部点达到0.2 MPa。地震应变在东、西盆地有明显的分异,但量值总体保持在10-5,只在局部异常点达到10-4,不会在盆地区内形成地表裂缝等破坏,对建筑结构的永久变形影响也较小。但应注意盆地边缘地貌单元分界处与断层附近的局部异常影响及其可能触发的次生灾害。
On the bases of the regional seismic tectonics,deep geophysical characters and the basin structure of Lanzhou area,the 3D seismotectonic model is created for earthquake occurring on west part of north Mahanshan fault,and the earthquake deformation influence to Lanzhou basin is calculated on the case of earthquake MS=7.The results show that the deformation in Lanzhou basin has certain degree of attenuation and the total displacement of ground surface is from 1.25 m to 0.3 m from west to east of the basin.The maximum earthquake stress is about 0.02 MPa in the basin and only reached to 0.2 MPa on parts of the basin edge and front of high terraces.Although the earthquake strain has differentiation in east basin and west basin,the main strain magnitude is 10-5 and only a few abnormal points reachs to 10-4.The deformation would not cause destruction such as ground fracture,and the effect to buildings′ permanent deformation is weak also.But we should pay attention to the local abnormal effect near the boundaries of geomorphic elements and faults as well as the secondary hazard may be triggered.
On the bases of the regional seismic tectonics,deep geophysical characters and the basin structure of Lanzhou area,the 3D seismotectonic model is created for earthquake occurring on west part of north Mahanshan fault,and the earthquake deformation influence to Lanzhou basin is calculated on the case of earthquake MS=7.The results show that the deformation in Lanzhou basin has certain degree of attenuation and the total displacement of ground surface is from 1.25 m to 0.3 m from west to east of the basin.The maximum earthquake stress is about 0.02 MPa in the basin and only reached to 0.2 MPa on parts of the basin edge and front of high terraces.Although the earthquake strain has differentiation in east basin and west basin,the main strain magnitude is 10-5 and only a few abnormal points reachs to 10-4.The deformation would not cause destruction such as ground fracture,and the effect to buildings′ permanent deformation is weak also.But we should pay attention to the local abnormal effect near the boundaries of geomorphic elements and faults as well as the secondary hazard may be triggered.
引文
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[19]曾海容,宋惠珍.利用三维有限单元格林函数反演1989年Loma Prieta地震的震源机制[J].地震学报,1999,21(3):225-232.
[20]王爱国,石玉成,马巍.地震地表变形三维有限元数值分析[J].岩石力学与工程学报,2004,23(24):4124-4130.
[21]王爱国,石玉成,柳煜.黄河黑山峡大柳树坝址区最大潜在地震变形及地震应力模拟预测[J].西北地震学报,2007,29(4):314-318.
[22]郭增建,秦保燕.震源物理[M].北京:地震出版社,1979.
[23]李善邦.中国地震[M].北京:地震出版社,1981
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[25]Christensen N I,Mooney W D.Seismic velocity structure andcomposition of the continental crust:a global view[J].J.G.R.,1995 100(B7):9761-9788
[2]袁道阳,王兰民,何文贵,等.兰州市活断层探测新进展[J].地震地质,2008,30(1):236-249.
[3]K Kasahara.The nature of seismic origins as inferred from seismo-logical and geodetic observations(Ⅰ)[J].B.E.R.I.,1957,35(3):473-532.
[4]K Kasahara.Physical conditions of earthquake faults(Ⅱ),Amodel of strike-slip faults with various dip angles[J].B.E.R.I.1959,37(1):39-52.
[5]L Knopoff.Energy release in earthquakes[J].Geophys,J.R.A.S.,1958,1(1):44-52.
[6]MAChinnery.The deformation of the ground around surface faults[J].B.S.S.A.,1961,51(3):355-372.
[7]TMarayama.Statical elastic dislocation in an infinite and semi-infinite medium[J].Bull.Earthq.Res.Inst.,Tokyo Univ.,1964,42(2):355-372.
[8]F Press.Displacements,strains and tilts at teleseismic distances[J].J.G.R.,1965,70(10):2395-2412.
[9]MAChinnery,J APetrak.The dislocation fault model with a var-iable discontinuity[J].Tectonophysics,1968,5(6):513-529.
[10]N Canitez,MNTokosoz.Static and dynamic study of earthquakesource mechanism:San Fernando earthquake[J].J.G.R.,1972,77(14):2583-2594.
[11]陈运泰,林邦慧,林中洋,等.根据地面形变的观测研究1966年邢台地震的震源过程[J].地球物理学报,1975,18(3):164-182.
[12]Okada Y.Surface deformation due to shear and tensile fault in ahalf space[J].Bull.Seismol.Soc.Am.,1985,75(4):1135-1145.
[13]黄立人,顾国华.静力位错理论[M].北京:地震出版社,1982.
[14]Segall P,Harris R.Earthquake deformation cycle on the San An-dress fault near Parkfield,California[J].J.Geophys,Res.,1987,92(B10):10511-10525.
[15]宋惠珍,刘洁,兰印刚.位错模型的有限单元公式[J].西北地震学报,1993,15(2):6-12.
[16]Segall P,Lisowski M.Surface displacements in the 1906 SanFrancisco and 1989 Loma Prieta earthquakes[J].Science,1990,250(9):1241-1244.
[17]Thora A,Segall P.The 1989 Loma Prieta earthquake imagedfrom inversion of geodetic data[J].J.Geophys Res.,1994,99(B11):21 835-21855.
[18]曾海容,宋惠珍.三维有限单元反演的数学方法[J].地质力学学报,1999,5(1):45-49.
[19]曾海容,宋惠珍.利用三维有限单元格林函数反演1989年Loma Prieta地震的震源机制[J].地震学报,1999,21(3):225-232.
[20]王爱国,石玉成,马巍.地震地表变形三维有限元数值分析[J].岩石力学与工程学报,2004,23(24):4124-4130.
[21]王爱国,石玉成,柳煜.黄河黑山峡大柳树坝址区最大潜在地震变形及地震应力模拟预测[J].西北地震学报,2007,29(4):314-318.
[22]郭增建,秦保燕.震源物理[M].北京:地震出版社,1979.
[23]李善邦.中国地震[M].北京:地震出版社,1981
[24]马瑾.构造物理学概论[M].北京:地震出版,1987.
[25]Christensen N I,Mooney W D.Seismic velocity structure andcomposition of the continental crust:a global view[J].J.G.R.,1995 100(B7):9761-9788
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