平面应变双轴压缩岩样剪应力异常及破坏过程模拟
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摘要
利用FLAC,模拟了双轴压缩岩样的破坏过程及剪应力异常.在峰值强度之前及之后,岩石的本构模型分别取为线弹性及莫尔库仑剪破坏与拉破坏复合的应变软化模型.本文仅分析了3个具有较大应力降的周期的剪应力异常及塑性区分布.在第1及第2周期,剪破坏分别发生在试样的两侧及背景空区内部,前兆明显,地震属于断错型.在第3周期,背景空区之外的新剪切破裂带引起断错型地震;空区内部的老破裂带引起走滑型地震,未观测到前兆.在塑性区边缘,剪应力梯度较高.破裂带位置剪应力值反而较低.尽管在应力-应变曲线的软化阶段之前,不同单元的剪应力表现出千姿百态的复杂形态,但尚有规律可循.若几个单元都位于某条破裂带上,则剪应力的变化可能是同步的,或演变规律类似.鉴于原地复发地震类型可能不同,前兆将有差别.
The anomalies of shear stress and failure process of a rock specimen under biaxial plane strain compression are modeled using Fast Lagrangian Analysis of Continua(FLAC).In the elastic stage,the adopted constitutive relation is linear elasticity.In the strain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off is used and the post-peak constitutive relation is linear.The anomalies of shear stress in three periods with marked stress decrease beyond the peak stresses are analyzed.In the first and second periods,shear failure occurs on the specimen sides and in the gap,respectively,and earthquakes belong to the rupture type with apparent precursors.In the third period,new shear failure occurring outside the gap leads to rupture earthquakes;shear failure in the gap results in strike-slip earthquakes without precursor.In the process of failure,higher shear stress gradients appear in the shear fracture zone boundaries.Shear stress is lower at the zone center,reflecting the strain-softening behavior of rock in the zone.In the short-term stage,the migration is opposite.Though the anomalies of shear stress are especially complex prior to the strain-softening stages of the stress-strain curve,the shear stresses of different elements have similar or synchronous evolutionary regularities if the monitored elements are located at the same fracture zones.Precursors of shear stress on the condition of recurrence of earthquakes are possibly different due to different earthquake types.
The anomalies of shear stress and failure process of a rock specimen under biaxial plane strain compression are modeled using Fast Lagrangian Analysis of Continua(FLAC).In the elastic stage,the adopted constitutive relation is linear elasticity.In the strain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off is used and the post-peak constitutive relation is linear.The anomalies of shear stress in three periods with marked stress decrease beyond the peak stresses are analyzed.In the first and second periods,shear failure occurs on the specimen sides and in the gap,respectively,and earthquakes belong to the rupture type with apparent precursors.In the third period,new shear failure occurring outside the gap leads to rupture earthquakes;shear failure in the gap results in strike-slip earthquakes without precursor.In the process of failure,higher shear stress gradients appear in the shear fracture zone boundaries.Shear stress is lower at the zone center,reflecting the strain-softening behavior of rock in the zone.In the short-term stage,the migration is opposite.Though the anomalies of shear stress are especially complex prior to the strain-softening stages of the stress-strain curve,the shear stresses of different elements have similar or synchronous evolutionary regularities if the monitored elements are located at the same fracture zones.Precursors of shear stress on the condition of recurrence of earthquakes are possibly different due to different earthquake types.
引文
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[18]范燕,车兆宏.南北地震带北段及其两侧断层现今活动性[J].地震,2001,21(2):87~93.Fan Y,Che Z H.The fault activity in recent time alongnorthern section of North-South seismic belt and its bothsides[J].Earthquake,2001,21(2):87~93.
[19]王学滨.平面应变压缩岩样侧向变形特征数值模拟[J].岩土工程学报,2005,27(5):525~530.Wang X B.Numerical simulation of lateral deformation ofrock specimen in plane strain compression[J].Chinese Jour-nal of Geotechnical Engineering,2005,27(5):525~530.
[20]焦明若,张国民.地震前兆复杂性成因机理研究的讨论(一)——地震前兆复杂性的表现形式[J].地震,1998,18(1):14~20.Jiao M R,Zhang G M.Study on genetic mechanism of seis-mic precursory complexity(I):The manifestation of the seis-mic precursory complexity[J].Earthquake,1998,18(1):14~20.
[21]梅世蓉.地震前兆的地区性[J].中国地震,1985,1(2):17~23.Mei S R.Regionalism of earthquake precursors[J].Earth-quake Research in China,1985,1(2):17~23.
[22]陈棋福.中国震例(1995~1996)[M].北京:地震出版社,2002.Chen Q F.Earthquake cases in China(1995~1996)[M].Beijing:Earthquake Press,2002.
[23]朱令人,周仕勇,杨马陵,等.地震复杂性前兆与强震多重分形谱异常[J].地震,1997,17(4):331~339.Zhu L R,Zhou S Y,Yang M L,et al.Earthquake complexi-ty precursor and anomaly of multi-fractal spectrum of strongearthquakes[J].Earthquake,1997,17(4):331~339.
[24]罗灼礼,丁鉴海,刘德富,等.我国地震预报研究概述[J].地震,1997,17(3):317~324.Luo Z L,Ding J H,Liu D F,et al.Review on earthquakeprediction research in China[J].Earthquake,1997,17(3):317~324.
[2]尹京苑,梅世蓉.地壳应力状态及其三维模型计算中的意义[J].地震,1998,18(3):226~322.Yin J Y,Mei S R.The crustal stress state and its significancein three dimensional simulations[J].Earthquake,1998,18(3):226~322.
[3]谢富仁,陈群策,崔效锋,等.中国大陆地壳应力环境基础数据库[J].地球物理学进展,2007,22(1):131~136.Xie F R,Chen Q C,Cui X F,et al.Fundamental database ofcrustal stress environment in continental China[J].Progress inGeophysics,2007,22(1):131~136.
[4]李均之,陈维升,夏雅琴,等.昆仑山口西Ms8.1级地震前兆[J].地球物理学进展,2006,21(2):340~344.Li J Z,Chen W S,Xia Y Q,et al.The precursors of Ms8.1earthquake occurred in west of mountain gap of Kunlun,China[J].Progress in Geophysics,2006,21(2):340~344.
[5]陈培善,荣玉仿,白彤霞.断裂力学地震破裂模式和应力降模式的比较及其应用[J].地球物理学报,2002,45(增):175~188.Chen P S,Rong Y F,Bai T X.Comparison between the frac-ture mechanics earthquake rupture model and the stress dropmodel and its application to estimation of tectonic ambientshear stress value[J].Chinese Journal of Geophysics,2002,45(Supp.):175~188.
[6]梅世蓉.地震前兆场物理模式与前兆时空分布机制研究(二)[J].地震学报,1996,18(1):1~10.Mei S R.On the physical model of earthquake precursor fieldsand the mechanism of precursors'timespace distribution(II)[J].Acta Seismologica Sinica,1996,18(1):1~10.
[7]马胜利,马瑾.我国实验岩石力学与构造物理学研究的若干新进展[J].地震学报,2003,25(5):453~464.Ma S L,Ma J.Recent progress in studies of experimental rockmechanics and tectonophysics in China[J].Acta SeismologicaSinica,2003,25(5):453~464.
[8]王仁.有限单元等数值方法在我国地球科学中的应用和发展[J].地球物理学报,1994,37(增1):128~139.Wang R.Application and development of finite element andother numerical simulation methods in earth sciences in China[J].Chinese Journal of Geophysics,1994,37(Supp.1):128~139.
[9]焦明若,唐春安,张国民,等.细观非均匀性对岩石破裂过程和微震序列类型影响的数值试验研究[J].地球物理学报,2003,46(5):659~666.Jiao M R,Tang C A,Zhang G M,et al.Numerical test of in-fluence of mesoscopic heterogeneity on macroscopic behavior ofrock failure and seismic sequence types[J].Chinese Journal ofGeophysics,2003,46(5):659~666.
[10]王学滨,赵扬锋,代树红,等.地震块体模型的共轭剪切破裂带数值模拟[J].防灾减灾工程学报,2004,24(2):119~125.Wang X B,Zhao Y F,Dai S H,et al.Numerical simulationof conjugate shear fracture bands for seismic block model[J].Journal of Disaster Prevention and Mitigation Engineering,2004,24(2):119~125.
[11]马瑾.从断层中心论向块体中心论转变~论活动块体在地震活动中的作用[J].地学前缘,1999,6(6):363~370.Ma J.Changing viewpoint from fault to block—a discussionabout the role of active block in seismicity[J].Earth ScienceFrontiers(China University of Geosciences,Beijing),1999,6(6):363~370.
[12]王学滨.地震前兆特征与岩样剪切应变率异常数值模拟[J].大地测量与地球动力学,2005,25(1):102~107,122.Wang X B.Numerical simulation of anomalies in shear strainrate of rock in biaxial plane strain compression[J].Journal ofGeodesy and Geodynamics,2005,25(1):102~107,122.
[13]李献智,李丽,赵成达.短期前兆动态变化与地震关系的研究[J].地震,1997,17(2):149~156.Li X Z,Li L,Zhao C D.On the relationship between seis-micity and dynamic changes of the short-term precursors[J].Earthquake,1997,17(2):149~156.
[14]陈立德.强震中短期前兆异常的共性特征[J].地震,2000,20(2):7~13.Chen L D.Common features of medium-and short-term pre-cursory anomalies before strong earthquakes[J].Earth-quake,2000,20(2):7~13.
[15]牛安福,张晶,延旭东,等.西南地区强震前后地壳变形异常强度场特征研究[J].地震,2002,22(1):61~69.Niu A F,Zhang J,Yan X D,et al.On the characteristics ofanomaly deformation field around strong earthquakes inSouthwest China area[J].Earthquake,2002,22(1):61~69.
[16]张国民.我国地震监测预报研究的主要科学进展[J].地震,2002,22(1):1~8.Zhang G M.The main science advance of earthquake monito-ring and prediction in China[J].Earthquake,2002,22(1):1~8.
[17]宋治平,徐平,薛艳.华北地区震群活动的阶段性特征[J].地震,2001,21(1):47~52.Song Z P,Xu P,Xue Y.Stage-by-stage characteristics ofearthquake swarm activity in the North China region[J].Earthquake,2001,21(1):47~52.
[18]范燕,车兆宏.南北地震带北段及其两侧断层现今活动性[J].地震,2001,21(2):87~93.Fan Y,Che Z H.The fault activity in recent time alongnorthern section of North-South seismic belt and its bothsides[J].Earthquake,2001,21(2):87~93.
[19]王学滨.平面应变压缩岩样侧向变形特征数值模拟[J].岩土工程学报,2005,27(5):525~530.Wang X B.Numerical simulation of lateral deformation ofrock specimen in plane strain compression[J].Chinese Jour-nal of Geotechnical Engineering,2005,27(5):525~530.
[20]焦明若,张国民.地震前兆复杂性成因机理研究的讨论(一)——地震前兆复杂性的表现形式[J].地震,1998,18(1):14~20.Jiao M R,Zhang G M.Study on genetic mechanism of seis-mic precursory complexity(I):The manifestation of the seis-mic precursory complexity[J].Earthquake,1998,18(1):14~20.
[21]梅世蓉.地震前兆的地区性[J].中国地震,1985,1(2):17~23.Mei S R.Regionalism of earthquake precursors[J].Earth-quake Research in China,1985,1(2):17~23.
[22]陈棋福.中国震例(1995~1996)[M].北京:地震出版社,2002.Chen Q F.Earthquake cases in China(1995~1996)[M].Beijing:Earthquake Press,2002.
[23]朱令人,周仕勇,杨马陵,等.地震复杂性前兆与强震多重分形谱异常[J].地震,1997,17(4):331~339.Zhu L R,Zhou S Y,Yang M L,et al.Earthquake complexi-ty precursor and anomaly of multi-fractal spectrum of strongearthquakes[J].Earthquake,1997,17(4):331~339.
[24]罗灼礼,丁鉴海,刘德富,等.我国地震预报研究概述[J].地震,1997,17(3):317~324.Luo Z L,Ding J H,Liu D F,et al.Review on earthquakeprediction research in China[J].Earthquake,1997,17(3):317~324.
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