地震断层粘滑错动对青藏铁路变形效应的有限元分析——以东昆仑活动断裂为例
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摘要
东昆仑断裂是青藏高原北部现今仍在强烈活动的左旋走滑地震断裂之一,该断裂的未来地震活动及其突发性粘滑错动是青藏铁路面临的重大工程地质问题。本文基于断裂几何学和运动学特征,通过加入8m的水平左旋位移,模拟了东昆仑断裂未来地震活动震中位于铁路线附近时铁路变形效应。结果表明,震中位于铁路线附近时,基岩整体移动,而第四纪松散层和道床则发生了变形,靠近断裂带附近的第四系自下而上水平位移明显减小,而铁轨和道床没有明显的断错,表现为长度约为25m的连续左旋弯曲变形;在铁路东、西两侧形成NE向的张裂陷和NW向的地震鼓包。在断裂带附近,铁轨发生了严重扭曲,铁轨应力自断裂带向两侧逐渐降低,而且铁轨的最大剪应力平面与铁轨的延伸方向垂直,因而在地震影响下,铁轨最有可能发生的破坏是剪切性的,并提出加宽路基、置换土层等工程防治措施。
The East Kunlun fault(EKF) is one of the present-day most active,left-lateral strike-slip seismogenic faults in the northern Qinghai-Tibet Plateau.Future seismic activities or abrupt strike-slip movement of the EKF will cause serious engineering-geological problems to the Qinghai-Tibet Railway.On the basis of the geometric and kinematic characteristics of the EKF,the deformation effects of the rails occurring when the epicenter of a future earthquake is located near the railway were simulated,with 8 m horizontal left-lateral displacement added.The results show that the bedrock moves 8 m en masse when the epicenter is located near the railway,while the Quaternary loose sediments and groundsill are deformed.The horizontal diaplacement of the Quaternary close to the fault is obviously smaller from above downward,while the rails and groundsill show successive left-lateral crooked deformation for about 25 m.There occur a NE-trending tensional graben and a NW-trending seismic drumlin on the east and west sides of the railway respectively.The rails are seriously distorted near the fault and the stress of the rails is reduced toward both sidess of the fault and the maximum shear stress plane of the rails is perpendicular to the direction of elongation of the rails;therefore the rails are most likely to be subjected to shear once an earthquake happens.On the basis of the simulation,the paper puts forward such countermeasures as widening of the groundsill and replacement of the soil layer near the fault.
The East Kunlun fault(EKF) is one of the present-day most active,left-lateral strike-slip seismogenic faults in the northern Qinghai-Tibet Plateau.Future seismic activities or abrupt strike-slip movement of the EKF will cause serious engineering-geological problems to the Qinghai-Tibet Railway.On the basis of the geometric and kinematic characteristics of the EKF,the deformation effects of the rails occurring when the epicenter of a future earthquake is located near the railway were simulated,with 8 m horizontal left-lateral displacement added.The results show that the bedrock moves 8 m en masse when the epicenter is located near the railway,while the Quaternary loose sediments and groundsill are deformed.The horizontal diaplacement of the Quaternary close to the fault is obviously smaller from above downward,while the rails and groundsill show successive left-lateral crooked deformation for about 25 m.There occur a NE-trending tensional graben and a NW-trending seismic drumlin on the east and west sides of the railway respectively.The rails are seriously distorted near the fault and the stress of the rails is reduced toward both sidess of the fault and the maximum shear stress plane of the rails is perpendicular to the direction of elongation of the rails;therefore the rails are most likely to be subjected to shear once an earthquake happens.On the basis of the simulation,the paper puts forward such countermeasures as widening of the groundsill and replacement of the soil layer near the fault.
引文
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[2]董治平,张守洁,简春林.青藏铁路未来地震灾害问题讨论[J].灾害学,2003,18(4):35~39.
[3]青海省地震局.东昆仑活动断裂带[M].北京:地震出版社,1999.1~186.
[4]刘光勋.东昆仑活动断裂带及其强震活动[J].中国地震,1996,12(2):119~126.
[5]党光明,王赞军.青海昆仑山口西MS8.1级地震地表破裂代特征与主要震害———对青藏高原区域稳定性评价的制约[J].地质通报,2002,21(2):105~108.
[6]Lin A,Fu B,Guo J et al.Co-seismin strike-slip and rupture length produced by the 2001 Ms 8.1 Central Kunlun earthquake[J].Science,2002,296(14):2015~2017.
[7]吴树仁,李贵书,何锋,等.昆仑山地震地表破裂带东段几何学与运动学[J].地质通报,2002,21(8~9):554~561.
[8]赵瑞斌,李军,向志勇,等.昆仑山口西8.1级地震地表破裂带西段考察[J].内陆地震,2002,16(2):175~179.
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