黄土覆盖的阶地陡坎附近渭河断裂活断层探测
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摘要
陕西咸阳渭河北岸窑店、石何杨、杜家堡渭河断裂活断层探测结果表明,对于有黄土覆盖的、与阶地陡坎重合的活断层探测,要综合采用地形地貌分析、浅层人工地震、钻探和探槽等方法进行。特别是对于钻孔探测,要深、中、浅孔结合。首先用中、深孔确定断层在深部的位置,再用浅孔确定断层在近地表的位置和活动性。由于河流侵蚀,阶地陡坎区的河流相沉积地层是倾斜的,风成的古土壤层披盖在已有的倾斜地层上亦呈倾斜状态,因此,用以上地层判断断层的位置和活动量时,钻孔孔距一定要小,以2～3m为宜,孔距太大,会把侵蚀形成的已有陡坎高度加入断层的错距中,严重放大断层的错动量。探测结果表明,渭河断裂在窑店、石何杨、杜家堡等处与Ⅲ级阶地陡坎重合。该断裂在阶地陡坎上的活动量很小,错断晚更新世第1古土壤层1～2m,远小于2个阶地面的高差。可见,以前认为S1错距4.8m、17.94m是不准确的。
Based on the survey and study of active faults at three sites,i.e.Yaodian,Shiheyang and Dujiapu on the north bank of Weihe River in Xianyang,Shaanxi,this paper probes into the methodology of survey of the loess-covered active faults coincident with terrace scarps,and presents the displacement amount of the Weihe Fault zone at Shiheyang in late Pleistocene.At Shiheyang,exploration of the Weihe Fault zone was carried out by means of shallow seismic prospecting,drilling,topographic analysis and age dating.The initial survey result showed a displacement of 17.94m of the stratum S1 on the Weihe Fault zone.The causes leading to this false result were mainly due to incorrect judgment on geomorphic unit,and followed by the so big spacing of drill holes that the subtle change of strata tilting due to erosion couldn't be seen.The drop of the same stratum at the profile detected at two drill holes far away from each other was mistaken for fault displacement.With the scarp caused by erosion added to the fault displacement,the fault throw was magnified.By densifying the drill holes to a spacing of 1.9m between holes,we get the displacement of the top of S1 to be only about 1.2m.At Yaodian,data are available,including the 200m deep drilling section data,the densified mid-deep drilling data and shallow seismic prospecting data.Drilling data with borehole spacing of 30m revealed an offset of 4.8m on the top of S1 by the Weihe Fault.Since the two holes were located at scarp change zone,the 4.8m height difference of the top of S1 might be the elevation difference of tilted terrain superimposed possibly with certain amount of faulting.The 30m hole spacing is too large to affirm that S1 has been faulted.The drilling section at Dujiapu was implemented at last,in which deficiencies in dealing with the first two ones were avoided.At this site,the shallow seismic methods couldn't be performed,therefore the fault was located by combining the deep drilling with shallow drilling at a hole spacing as small as possible(2～3m).In spite of the small borehole spacing,it was difficult to identify the displacement amount of the fault according to the paleosol layer S1,which is probably due to too small fault throw.All the explorations of fault at the above three sites have a certain deficiency in methodology,mainly in the depth and spacing of drill holes.The common shortcoming is that no deep trenches were excavated.If allowable,it would be better to verify the fault location and activity by trenching.The above results show that the exploration of loess-covered active faults coincident with terrace scarps shall be carried out with comprehensive method combining topographic analysis,shallow seismic survey,drilling and trenching.Particularly for drilling exploration,deep,medium and shallow holes shall be combined in use with the medium and deep holes drilled to determine the location of faults at depth,and the shallow holes used to identify the location and activity of faults near surface.Due to river erosion,the fluvial deposition layer in terrace scarp zone is tilted.Aeolian paleosol layer draping over the tilted layer is tilted too.As a result,the spacing between holes must be small(2～3m preferable)when such strata are used to identify the location and movement of faults.Excessive spacing may lead to the addition of the height of erosion-formed scarp to the fault offset,thus greatly overstating the later.It is highly recommended to make verification by trenching in the end.The above exploration results show that the Weihe Fault zone coincides with the scarps of the third terrace at Yaodian,Shiheyang and Dujiapu.The displacements associated with faulting only have a small proportion of the terrace scarp and the 1～2m offset of the first late Pleistocene paleosol layer by faulting is much less than the difference in elevation of terrace surface.The previously thought 4.8m and 17.94m displacements are incorrect.
Based on the survey and study of active faults at three sites,i.e.Yaodian,Shiheyang and Dujiapu on the north bank of Weihe River in Xianyang,Shaanxi,this paper probes into the methodology of survey of the loess-covered active faults coincident with terrace scarps,and presents the displacement amount of the Weihe Fault zone at Shiheyang in late Pleistocene.At Shiheyang,exploration of the Weihe Fault zone was carried out by means of shallow seismic prospecting,drilling,topographic analysis and age dating.The initial survey result showed a displacement of 17.94m of the stratum S1 on the Weihe Fault zone.The causes leading to this false result were mainly due to incorrect judgment on geomorphic unit,and followed by the so big spacing of drill holes that the subtle change of strata tilting due to erosion couldn't be seen.The drop of the same stratum at the profile detected at two drill holes far away from each other was mistaken for fault displacement.With the scarp caused by erosion added to the fault displacement,the fault throw was magnified.By densifying the drill holes to a spacing of 1.9m between holes,we get the displacement of the top of S1 to be only about 1.2m.At Yaodian,data are available,including the 200m deep drilling section data,the densified mid-deep drilling data and shallow seismic prospecting data.Drilling data with borehole spacing of 30m revealed an offset of 4.8m on the top of S1 by the Weihe Fault.Since the two holes were located at scarp change zone,the 4.8m height difference of the top of S1 might be the elevation difference of tilted terrain superimposed possibly with certain amount of faulting.The 30m hole spacing is too large to affirm that S1 has been faulted.The drilling section at Dujiapu was implemented at last,in which deficiencies in dealing with the first two ones were avoided.At this site,the shallow seismic methods couldn't be performed,therefore the fault was located by combining the deep drilling with shallow drilling at a hole spacing as small as possible(2～3m).In spite of the small borehole spacing,it was difficult to identify the displacement amount of the fault according to the paleosol layer S1,which is probably due to too small fault throw.All the explorations of fault at the above three sites have a certain deficiency in methodology,mainly in the depth and spacing of drill holes.The common shortcoming is that no deep trenches were excavated.If allowable,it would be better to verify the fault location and activity by trenching.The above results show that the exploration of loess-covered active faults coincident with terrace scarps shall be carried out with comprehensive method combining topographic analysis,shallow seismic survey,drilling and trenching.Particularly for drilling exploration,deep,medium and shallow holes shall be combined in use with the medium and deep holes drilled to determine the location of faults at depth,and the shallow holes used to identify the location and activity of faults near surface.Due to river erosion,the fluvial deposition layer in terrace scarp zone is tilted.Aeolian paleosol layer draping over the tilted layer is tilted too.As a result,the spacing between holes must be small(2～3m preferable)when such strata are used to identify the location and movement of faults.Excessive spacing may lead to the addition of the height of erosion-formed scarp to the fault offset,thus greatly overstating the later.It is highly recommended to make verification by trenching in the end.The above exploration results show that the Weihe Fault zone coincides with the scarps of the third terrace at Yaodian,Shiheyang and Dujiapu.The displacements associated with faulting only have a small proportion of the terrace scarp and the 1～2m offset of the first late Pleistocene paleosol layer by faulting is much less than the difference in elevation of terrace surface.The previously thought 4.8m and 17.94m displacements are incorrect.
引文
[1]国家地质总局第三普查大队,1977,汾渭盆地石油普查阶段地质成果报告。
[2]陕西省地质矿产局第一水文队,1987,渭河发电厂扩建工程供水西部水源地水文地质勘察报告。
[3]西北电力设计院,1979,渭河电厂一期工程供水水文地质勘察报告。
[4]陕西省地震局,1990,咸阳市地震小区划工作报告。
[1]同9页[2]。
[1]长安大学工程技术研究院,2000,西安咸阳国际机场高速公路工程物探勘察报告。
[2]咸阳市城乡建设规划局,咸阳市勘察测绘院,2007,咸阳工程地质图集。
[1]陕西省工程地震勘察研究院,2005,西郑铁路工程场地地震安全性评价报告。
常旭,吴国雄,郭迁.2006.溜砂坡形成机理及防治措施研究[J].公路,(1):89—91.CHANG Xu,WU Guo-xiong,GUO Qian.2006.The study of formation mechanism and prevention measure of sand-sliding slope[J].Highway,(1):89—91(in Chinese).
冯希杰,戴王强,董星宏.2003a.从陕西省扶风县古水路堑剖面剖析渭河断裂第四纪活动[J].中国地震,19(2):188—193.FENG Xi-jie,DAI Wang-qiang,DONG Xing-hong.2003a.Quaternary activity of the Weihe Fault obtained from theanalysis of Gushui trough profile in Fufeng county,Shaanxi Province[J].Earthquake Research in China,19(2):188—193(in Chinese).
冯希杰,田勤俭,申旭辉.2003b.渭河断裂西段活动差异性分析[J].地质论评,49(3):233—238.FENG Xi-jie,TIAN Qin-jian,SHEN Xu-hui.2003b.Analysis of activity difference of the west section of the WeiheFault[J].Geological Review,49(3):233—238(in Chinese).
国家地震局鄂尔多斯周缘活动断裂系课题组.1988.鄂尔多斯周缘活动断裂系[M].北京:地震出版社.Research group of active fault system around Ordos massif,State Seismological Bureau.1988.Active Fault Systemaround Ordos Massif[M].Seismological Press,Beijing(in Chinese).
刘俊峰,罗长胜,刘渭.2003.陕西咸阳市某厂工程场地地裂缝初步研究[J].地质灾害与环境保护,14(4):6—10.LIU Jun-feng,LUO Chang-sheng,LIU Wei.2003.Preliminary study on the ground fissure in one plant engineeringsite,Shaanxi Province[J].Journal of Geological Hazards and Environment Preservation,14(4):6—10(inChinese).
石雨亮,陆晶,詹义正,等.2007.泥沙的水下休止角与干容重计算[J].武汉大学学报(工学版),40(3):14—17.SHI Yu-liang,LUJing,ZHANYi-zheng,et al.2007.Calculation of angle of repose and dry density of sediment[J].Engineering Journal of Wuhan University,40(3):14—17(in Chinese).
师亚芹,李晋,冯希杰,等.2007.渭河断裂带古地震研究[J].地震地质,29(3):607—616.SHI Ya-qin,LI Jin,FENG Xi-jie,et al.2007.The study of paleoearthquake on the Weihe Fault zone[J].Seismology and Geology,29(3):607—616(in Chinese).
吴国雄,曾榕彬,王成华,等.2006.溜砂坡的形成诱发因素及失稳破坏条件[J].中国铁道科学,27(5):7—12.WU Guo-xiong,ZENG Rong-bin,WANG Cheng-hua,et al.2006.The inducing factors and the collapse conditions ofsand-sliding slope[J].China Railway Science,27(5):7—12(in Chinese).
詹义正,谢葆玲.1996.散体泥沙的水下休止角[J].水电能源,14(1):56—59.ZHAN Yi-zheng,XIE Bao-ling.1996.Under water angle of rest for non-cohesive sediment[J].International Journalof Hydroelectric Energy,14(1):56—59(in Chinese).
[2]陕西省地质矿产局第一水文队,1987,渭河发电厂扩建工程供水西部水源地水文地质勘察报告。
[3]西北电力设计院,1979,渭河电厂一期工程供水水文地质勘察报告。
[4]陕西省地震局,1990,咸阳市地震小区划工作报告。
[1]同9页[2]。
[1]长安大学工程技术研究院,2000,西安咸阳国际机场高速公路工程物探勘察报告。
[2]咸阳市城乡建设规划局,咸阳市勘察测绘院,2007,咸阳工程地质图集。
[1]陕西省工程地震勘察研究院,2005,西郑铁路工程场地地震安全性评价报告。
常旭,吴国雄,郭迁.2006.溜砂坡形成机理及防治措施研究[J].公路,(1):89—91.CHANG Xu,WU Guo-xiong,GUO Qian.2006.The study of formation mechanism and prevention measure of sand-sliding slope[J].Highway,(1):89—91(in Chinese).
冯希杰,戴王强,董星宏.2003a.从陕西省扶风县古水路堑剖面剖析渭河断裂第四纪活动[J].中国地震,19(2):188—193.FENG Xi-jie,DAI Wang-qiang,DONG Xing-hong.2003a.Quaternary activity of the Weihe Fault obtained from theanalysis of Gushui trough profile in Fufeng county,Shaanxi Province[J].Earthquake Research in China,19(2):188—193(in Chinese).
冯希杰,田勤俭,申旭辉.2003b.渭河断裂西段活动差异性分析[J].地质论评,49(3):233—238.FENG Xi-jie,TIAN Qin-jian,SHEN Xu-hui.2003b.Analysis of activity difference of the west section of the WeiheFault[J].Geological Review,49(3):233—238(in Chinese).
国家地震局鄂尔多斯周缘活动断裂系课题组.1988.鄂尔多斯周缘活动断裂系[M].北京:地震出版社.Research group of active fault system around Ordos massif,State Seismological Bureau.1988.Active Fault Systemaround Ordos Massif[M].Seismological Press,Beijing(in Chinese).
刘俊峰,罗长胜,刘渭.2003.陕西咸阳市某厂工程场地地裂缝初步研究[J].地质灾害与环境保护,14(4):6—10.LIU Jun-feng,LUO Chang-sheng,LIU Wei.2003.Preliminary study on the ground fissure in one plant engineeringsite,Shaanxi Province[J].Journal of Geological Hazards and Environment Preservation,14(4):6—10(inChinese).
石雨亮,陆晶,詹义正,等.2007.泥沙的水下休止角与干容重计算[J].武汉大学学报(工学版),40(3):14—17.SHI Yu-liang,LUJing,ZHANYi-zheng,et al.2007.Calculation of angle of repose and dry density of sediment[J].Engineering Journal of Wuhan University,40(3):14—17(in Chinese).
师亚芹,李晋,冯希杰,等.2007.渭河断裂带古地震研究[J].地震地质,29(3):607—616.SHI Ya-qin,LI Jin,FENG Xi-jie,et al.2007.The study of paleoearthquake on the Weihe Fault zone[J].Seismology and Geology,29(3):607—616(in Chinese).
吴国雄,曾榕彬,王成华,等.2006.溜砂坡的形成诱发因素及失稳破坏条件[J].中国铁道科学,27(5):7—12.WU Guo-xiong,ZENG Rong-bin,WANG Cheng-hua,et al.2006.The inducing factors and the collapse conditions ofsand-sliding slope[J].China Railway Science,27(5):7—12(in Chinese).
詹义正,谢葆玲.1996.散体泥沙的水下休止角[J].水电能源,14(1):56—59.ZHAN Yi-zheng,XIE Bao-ling.1996.Under water angle of rest for non-cohesive sediment[J].International Journalof Hydroelectric Energy,14(1):56—59(in Chinese).
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