上海地区地壳精细结构的综合地球物理探测研究
摘要
通过在上海地区开展深、浅地震反射、地震宽角反射/折射、高分辨地震折射和大地电磁测深等联合剖面探测,获得了该地区近地表至Moho面的精细速度结构、电性结构和深浅构造关系.结果表明,该地区地壳可划分为上、中、下三个组成部分.其中,上地壳厚为12~14km,波速为5.7~5.9km/s;中地壳厚度约为10km,波速为5.9~6.2km/s;下地壳厚为10~11km,波速为6.2~6.3km/s,Moho面深度约为32km.剖面浅部地质构造复杂,共解释出12条特征明显的断裂.其中,除3条断裂错断结晶基底(G界面)并向下延伸至上地壳底界面外,其他断裂均在深度3~5km以上终止或收敛于G界面之上.此外,仅在剖面西侧基底下部约13~15km埋深处发现一厚度在2km左右的壳内高导层.所以,在综合各方面资料后分析认为,在剖面经过地区不存在发生大地震的深部构造条件,近地表所存在的活动断层是未来产生对该区有影响地震的震源区.
The fine seismic velocity structure, electrical conductivity structure and geometrical construction of the crust in Shanghai region and the coupled relationship between the deep and shallow structures are investigated by using multi_geophysics exploration methods, such as shallow seismic reflection, deep seismic reflection, high_resolution seismic refraction, deep seismic wide angle reflection/refraction and magnetotelluric sounding. The research results indicate that the crust in the region can be divided into three layers, namely upper, middle, and lower crust. The upper crust is 12～14km thick with a seismic velocity of 5.7～5.9km/s, the middle crust is about 10 km thick with a velocity of 5.9～6.2 km/s, and the lower crust is 10～11 km thick with a velocity of 6.2～6.3 km/s. The depth of Moho in the region is 31～33 km. There are 12 main faults explained in the experimental profile. Except for three faults, which have dislocated G interface (crystalline basement) and extended down to the bottom interface (whose depth is about 10 km) of the upper crust, the other faults have ended above G interface at 3 to 5 km depth, or have converged at G interface. Moreover, there is only a high conductivity layer (about 2 km thick) within crust at 13～15 km depth. Therefore, there is no deep structure condition for potential big earthquakes in the local region. However, the active rupture zones near the earth's surface are potential seismic source zone. The experimental profiling is the first high-resolution comprehensive deep survey profile in Shanghai and its conjoined regions.
The fine seismic velocity structure, electrical conductivity structure and geometrical construction of the crust in Shanghai region and the coupled relationship between the deep and shallow structures are investigated by using multi_geophysics exploration methods, such as shallow seismic reflection, deep seismic reflection, high_resolution seismic refraction, deep seismic wide angle reflection/refraction and magnetotelluric sounding. The research results indicate that the crust in the region can be divided into three layers, namely upper, middle, and lower crust. The upper crust is 12～14km thick with a seismic velocity of 5.7～5.9km/s, the middle crust is about 10 km thick with a velocity of 5.9～6.2 km/s, and the lower crust is 10～11 km thick with a velocity of 6.2～6.3 km/s. The depth of Moho in the region is 31～33 km. There are 12 main faults explained in the experimental profile. Except for three faults, which have dislocated G interface (crystalline basement) and extended down to the bottom interface (whose depth is about 10 km) of the upper crust, the other faults have ended above G interface at 3 to 5 km depth, or have converged at G interface. Moreover, there is only a high conductivity layer (about 2 km thick) within crust at 13～15 km depth. Therefore, there is no deep structure condition for potential big earthquakes in the local region. However, the active rupture zones near the earth's surface are potential seismic source zone. The experimental profiling is the first high-resolution comprehensive deep survey profile in Shanghai and its conjoined regions.
引文
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[14]Yu P,W J L,Wu J S.Using the pseudo-tipper data of magnetotelluric sounding to study fault.CPS/SEG2004International Geophyscial Conference,Beijing,2004,725~729
[15]于鹏,王家林,吴健生.有限差分法大地电磁多参数偏移成像.地球物理学报,2001,44(4):552~562Yu P,Wang J L,Wu J S.Multi-parameter migration imaging of magnetotelluric data using finite difference method.Chinese J.Geophys.(in Chinese),2001,44(4):552~562
[2]林命周.上海及其邻近海域”滨海地震学”研究简介.地震,2000,20(增刊):233~237Lin M Z.Research on littoral seismology in Shanghai and its neighboring sea area.Earthquake(in Chinese),2000,20(Suppl.):233~237
[3]陈沪生,周)清,李道琪,贺绍英.中国东部灵壁-奉贤(HQ-13)地学断面图(1∶1000000)说明书.北京:地质出版社,1993.1~73Chen HS,Zhou X Q,Li D Q,He S Y.Explanatory Notes of the Geoscience Transect of Lingbi-Fengxian(HQ-13)in Eastern China(1∶1000000)(in Chinese).Beijing:Geological Publishing House,1993.1~73
[4]国家地震局地学断面编委会.上海奉贤至内蒙古阿拉善左旗地学断面说明书.北京:地震出版社,1992.1~66Geoscience Transect Research Group of CSB.Explanatory Notes of the Geoscience Transect of Shanghai Fengxian-Neimenggu Alashan(in Chinese).Beijing:Seismological Press,1992.1~66
[5]Fuis GS.Images of crust beneath south California will aid study of earthquakes andtheir effects.EOS AGU,1996,77(4):173~176
[6]Fuis GS,Ryberg T,Lutter WJ.Seismic mapping of shallowfault zones in the San Gabriel Mountains fromthe Los Angeles Region Seismic Experiment,Southern California.J Geophys.Research,2001,106(B4):6549~6568
[7]朱金芳,徐锡伟,张先康等.福州盆地及邻区地壳精细结构的深地震反射与高分辨率折射及宽角反射/折射联合探测研究.中国科学(D辑),2005,35(8):738~749ZhuJ F,Xu X W,Zhang X K.Inspection and research on fine crust construction by using deep seismic reflection,high-resolution seismic refraction and seismic wide angle reflection/refraction.Science in China(Series D)(in Chinese),2005,35(8):738~749
[8]张先康,王椿镛,刘国栋等.延庆-怀来地区地壳细结构-利用深地震反射剖面.地球物理学报,1996,39(3):356~364Zhang X K,Wang C R,Liu G D.Fine crustal structure in Yanqing-Huailai region by deep seismic reflection profiling.Chinese J.Geophys.(in Chinese),1996,39(3):356~364
[9]王椿镛,王贵美,林中洋等.用深地震反射方法研究邢台地震区地壳细结构.地球物理学报,1993,36(4):445~452Wang C Y,Wang G M,Lin Z Y.Study onfine crustal structure by using deep seismic reflection method in Xingtai area.Chinese J.Geophys.(in Chinese),1993,36(4):445~452
[10]Sandmeier K J,Wenzel F.Synthetic seismograms for a complex crustal model.Geophysical Research Letters,1986,13(1):22~25
[11]上海地质矿产局.上海市区域地质志.北京:地质出版社,1998Geology Administration of Shanghai.Geology Records in Shanghai Region(in Chinese).Beijing:Geological Publishing House,1998
[12]陈乐寿,王光锷.大地电磁测深法.北京:地质出版社,1990Chen L S,Wang G E.Magnetotelluric Method(in Chinese).Beijing:Geological Publishing House,1990
[13]于鹏,王家林,吴健生.大地电磁全频段偏移成像结合反演技术.同济大学学报,2005,33(4):540~544Yu P,WangJ L,WuJ S.Magnetotelluric sounding wholefrequency bands migration imaging versus inversion technique.Journal of Tongji University(Natural Science)(in Chinese),2005,33(4):540~544
[14]Yu P,W J L,Wu J S.Using the pseudo-tipper data of magnetotelluric sounding to study fault.CPS/SEG2004International Geophyscial Conference,Beijing,2004,725~729
[15]于鹏,王家林,吴健生.有限差分法大地电磁多参数偏移成像.地球物理学报,2001,44(4):552~562Yu P,Wang J L,Wu J S.Multi-parameter migration imaging of magnetotelluric data using finite difference method.Chinese J.Geophys.(in Chinese),2001,44(4):552~562
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