新丰江库区上地壳三维细结构层析成像
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摘要
在新丰江库区布设一个范围约50km×40km、由50个地震临时台站组成的观测台阵,接收来自不同方位的人工震源产生的莫霍界面反射波;台阵中的20个台站和5个区域固定台还对2009年3月至2010年5月发生在库区的地方震进行了观测.本文联合利用人工地震莫霍面反射波走时和天然地震直达波走时,采用连续模型反演技术重建了库区上地壳P波、S波慢度扰动和Vp/Vs扰动分布图像.研究结果表明:新丰江库区东、西部地区上地壳结构存在明显的差异.库区东部地区构造复杂,多条断裂在该区呈交叉状分布.北西向的石角—新港—白田断裂带在库区段内具有复杂的岩性和构造特征,该断裂带在新港至双塘一线可能延伸至地下8km左右;近北东向的断裂带切割地壳较深.峡谷区及大坝以东附近地区存在上、下贯通的波速比高值区,尤其是大坝以西的深水峡谷区,存在一条顺河走向的陡倾角断层裂隙带,为库水渗透提供了良好通道.库区西部地区为相对稳定构造区,完整坚硬的花岗岩体透水性能较差,受库水渗透影响很小.新丰江水库诱发地震的形成与深部构造环境密切相关.峡谷区及大坝以东附近地区上地壳介质性质呈现明显的横向不均匀性,微震分布在介质物性结构的特定部位,"软"、"硬"交错的介质环境是倾滑正断层型微小震产生的可能原因.
A three-dimensional temporary seismic array with 50 stations was deployed in an approximately 50 km×40 km region around the Xinfengjiang reservoir to receive seismic waves generated by artificial sources from different azimuths.The local earthquakes occurred in the area from March 2009 to May 2010 were recorded by 20 stations of the seismic array and 5 permanent seismic stations.With the inversion method without model blocks,both reflection waves generated by the artificial sources from Moho at critical distances and direct waves from local earthquakes are used to reconstruct the 3-D images of P,S velocity and Vp/Vs perturbation of the upper crust under the seismic array.The results show that the upper crust structures below the Xinfengjiang reservoir area have significant differences between the eastern and the western region.The structure is complicated in the east of the reservoir where the faults intersect mutually.Under the reservoir,the NNW striking Shijiao-Xingang-Baitian fault zone has complex lithology and structural features,and from Xingang to Shuangtang,it probably extends down to 8 km depth.The fault zone of nearly NE direction cuts crust deep.There are through shallower and deeper high-velocity ratio zones in both the canyon and near the east of the Xinfengjiang dam,especially in the western deep water canyon region of Xinfengjiang dam,along the river there is a steep fault fracture zone.The high-velocity ratio zones provide a good channel for water infiltration.The west of reservoir is a relatively stable tectonic region,where intact and hard granite rock with low permeability has been affected little by reservoir water.The occurrence of Xinfengjiang reservoir-induced earthquakes is closely related to the deep structure environment.The upper crustal medium property in the canyon and near the east of the dam is obviously laterally heterogeneous.The micro earthquakes are located in the specific parts of medium physical property and structure.It is suggested that the "soft" and "hard" staggered media environment possibly leads to occurrence of dip-slip normal fault type micro earthquakes.
A three-dimensional temporary seismic array with 50 stations was deployed in an approximately 50 km×40 km region around the Xinfengjiang reservoir to receive seismic waves generated by artificial sources from different azimuths.The local earthquakes occurred in the area from March 2009 to May 2010 were recorded by 20 stations of the seismic array and 5 permanent seismic stations.With the inversion method without model blocks,both reflection waves generated by the artificial sources from Moho at critical distances and direct waves from local earthquakes are used to reconstruct the 3-D images of P,S velocity and Vp/Vs perturbation of the upper crust under the seismic array.The results show that the upper crust structures below the Xinfengjiang reservoir area have significant differences between the eastern and the western region.The structure is complicated in the east of the reservoir where the faults intersect mutually.Under the reservoir,the NNW striking Shijiao-Xingang-Baitian fault zone has complex lithology and structural features,and from Xingang to Shuangtang,it probably extends down to 8 km depth.The fault zone of nearly NE direction cuts crust deep.There are through shallower and deeper high-velocity ratio zones in both the canyon and near the east of the Xinfengjiang dam,especially in the western deep water canyon region of Xinfengjiang dam,along the river there is a steep fault fracture zone.The high-velocity ratio zones provide a good channel for water infiltration.The west of reservoir is a relatively stable tectonic region,where intact and hard granite rock with low permeability has been affected little by reservoir water.The occurrence of Xinfengjiang reservoir-induced earthquakes is closely related to the deep structure environment.The upper crustal medium property in the canyon and near the east of the dam is obviously laterally heterogeneous.The micro earthquakes are located in the specific parts of medium physical property and structure.It is suggested that the "soft" and "hard" staggered media environment possibly leads to occurrence of dip-slip normal fault type micro earthquakes.
引文
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[2]丁原章,潘建雄,肖安予等.新丰江水库诱发地震的构造条件.地震地质,1983,5(3):63-74.Ding Y Z,Pan J X,Xiao A Y,et al.Tectonic environment ofreservoir induced earthquake in the Xinfengjiang reservoirarea.Seismology and Geology(in Chinese),1983,5(3):63-74.
[3]潘建雄,肖安予.新丰江水库区地震构造及其活动特征的初步研究.地震地质,1982,4(2):53-58.Pan J X,Xiao A Y.The preliminary study of seismicstructures and their characteristic activity in Xinfengjiangreservoir area.Seismology and Geology(in Chinese),1982,4(2):53-58.
[4]王妙月,杨懋源,胡毓良等.新丰江水库地震的震源机制及其成因的初步探讨.中国科学(A辑),1976,(1):85-97.Wang M Y,Yang M Y,Hu Y L,et al.A preliminary studyon the mechanism of the reservoir impounding earthquakes atHsinfengkiang.Science in China,Ser.A(in Chinese),1976,(1):85-97.
[5]陈益明.新丰江水库地震及其小震震源机制的研究.华南地震,1982,2(3):64-71.Chen Y M.The focal mechanism study of Xinfengjiangreservoir-induced earthquakes and its micro aftershocks.South China Journal of Seismology(in Chinese),1982,2(3):64-71.
[6]丁原章,曾宪译,陈益明.新丰江水库区诱发地震的余震活动.地震地质,1982,4(1):23-29.Ding Y Z,Zeng X Y,Chen Y M.The aftershock activities ofinduced earthquakes in the Xinfengjiang reservoir areas.Seismology and Geology(in Chinese),1982,4(1):23-29.
[7]中国科学院地质研究所破裂与震源力学组,广东省科技局新丰江地震总结组.新丰江水库区微震震源力学的初步研究.地质科学,1974,(3):234-245.Focal mechanism and fracture researching group,Institute ofGeology,Academia Sinica,Hsinfengkiang earthquakesresearching group,Kwangtung Scientific and TechnologicalDepartment.A preliminary analysis of the mechanism ofmicroearthquakes in the region of Hsinfengkiang reservoir.Scientia Geologica Sinica(in Chinese),1974,(3):234-245.
[8]臧绍先.水的渗透作用及新丰江水库地震的特点和机制.地震地质,1983,5(2):59-69.Zang S X.The effect of infiltrating of water and mechanismand characteristics of earthquakes in Xinfengjiang reservoir.Seismology and Geology(in Chinese),1983,5(2):59-69.
[9]沈立英.渗流与新丰江水库地震.华南地震,1989,9(2):92-101.Shen L Y.The influent and earthquakes in Xinfengjiangreservoir.South China Journal of Seismology(in Chinese),1989,9(2):92-101.
[10]魏柏林,陈庞龙,李富光等.新丰江地震震源机制解及构造应力场.地震学报,1991,13(4):462-479.Wei B L,Chen P L,Li F G,et al.Focal mechanisms andtectonic stress field of the Xinfengjiang earthquakes.ActaSeismologica Sinica(in Chinese),1991,13(4):462-479.
[11]丁原章,王仁,孙荀英等.深层构造新活动性的影响——新丰江水库区构造的三维数学模拟计算.中国科学(B辑),1992,(2):194-205.Ding Y Z,Wang R,Sun X Y,et al.Influence of the deepstructure new activity—three-dimensional mathematicalsimulation of the tectonics in Xinfengjiang reservoir area.Science in China,Ser.B(in Chinese),1992,(2):194-205.
[12]胡毓良,陈献程.我国的水库地震及有关成因问题的讨论.地震地质,1979,1(4):45-57.Hu Y L,Chen X C.Discussion on the reservoir-inducedearthquakes in China and some problems related to theirorigin.Seismology and Geology(in Chinese),1979,1(4):45-57.
[13]李安然,徐永键,韩晓光等.中国东部四个水库震例的诱震环境因素研究.华南地震,1990,10(3):89-99.Li A R,Xu Y J,Han X G,et al.Environment factors ofinduced earthquake of four reservoirs in eastern China.SouthChina Journal of Seismology(in Chinese),1990,10(3):89-99.
[14]黄腾浪,杨马陵.新丰江地震S波偏振的初步研究.华南地震,2001,21(4):22-26.Huang T L,Yang M L.Preliminary study on polarization ofS-wave of Xinfengjiang earthquakes.South China Journal ofSeismology(in Chinese),2001,21(4):22-26.
[15]官幼雄,李亚林,颜玉定.1962年3月19日新丰江6.1级水库诱发地震时的构造应力.华南地震,2005,25(3):83-86.Gong Y X,Li Y L,Yan Y D.A study on the tectonic stressvariation caused by Xinfengjiang Ms6.1reservoir inducedearthquake occured on March 19,1962.South China Journalof Seismology(in Chinese),2005,25(3):83-86.
[16]万永芳,叶东华,陈大庆.广东新丰江地区地震研究.华南地震,2008,28(2):60-66.Wan Y F,Ye D H,Chen D Q.Study on earthquakecharacteristics in Xinfengjiang region.South China Journalof Seismology(in Chinese),2008,28(2):60-66.
[17]吴建春,冯锐,宋仲和.CT技术在新丰江台网中的应用.中国地震,1990,6(4):85-92.Wu J C,Feng R,Song Z H.Application of ComputerizedTomography on the Xinfengjiang Reservoir Network.Earthquake Research in China(in Chinese),1990,6(4):85-92.
[18]郭贵安,冯锐.新丰江水库三维速度结构和震源参数的联合反演.地球物理学报,1992,35(3):331-342.Guo G A,Feng R.The joint inversion of 3-D velocitystructure and source parameters in Xinfengjiang reservoir.Chinese Journal of Geophysics(in Chinese),1992,35(3):331-342.
[19]Tarantola A,Nercessian A.Three-dimensional inversionwithout blocks.Geophys.J.R.Astr.Soc,1984,76:299-306.
[20]张先康,杨卓欣,杨玉春等.地壳三维结构的层析成像方法—爆炸和地震资料的联合反演.地震学报,1995,17(4):422-431.Zhang X K,Yang Z X,Yang Y C,et al.Method oftomographic determination of the 3-D crustal structure:Jointinversion of explosion and earthquake data.Acta SeismologicaSinica(in Chinese),1995,17(4):422-431.
[21]王洪体,庄灿涛,薛兵等.精密主动地震监测.地球物理学报,2009,52(7):1808-1815.Wang H T,Zhuang C T,Xue B,et al.Precisely and activelyseismic monitoring.Chinese Journal of Geophysics(inChinese),2009,52(7):1808-1815.
[22]Nercessian A,Hirn A,Tarantola A.Three-dimensionalseismic transmission prospecting of the Mont Dore volcano,France.Geophys.J.R.Astr.Soc,1984,76:307-315.
[23]Tarantola A.Inverse Problem Theory:Methods for DataFitting and Model Parameter Estimation.New York:Elsevier Science Publ.Co.,1986:506-528.
[24]张先康,杨玉春,赵平等.唐山滦县震区的三维地震透射研究——中、上地壳速度层析成像.地球物理学报,1994,37(6):687-694.Zhang X K,Yang Y C,Zhao P,et al.Three-dimensionalseismic transmission experiment in the Luanxian earthquakeregion of North China:tomographic determination of theupper and middle crust structure.Chinese Journal ofGeophysics(in Chinese),1994,37(6):687-694.
[25]Zelt C A.Lateral velocity resolution from 3-D seismicrefraction data.Geophys.J.Int.,1998,135:1101-1112.
[26]王夫运,张先康,陈棋福等.北京地区上地壳三维细结构层析成像.地球物理学报,2005,48(2):359-366.Wang F Y,Zhang X K,Chen Q F,et al.Fine tomographicinversion of the upper crust 3-D structure around Beijing.Chinese Journal of Geophysics(in Chinese),2005,48(2):359-366.
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