中国大陆科学钻探工程地震资料采集处理与综合解释
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摘要
中国大陆科学钻探是举世瞩目的重大科学工程，江苏省东海县毛北地区以其独特的大地构造位置、大量的超高压变质岩以及丰富的深部信息等优越条件而成为第一个中国大陆科学钻探孔区。本文以在该区实施的两次地震勘探工作为素材，较为深入地研究了孔区的地震响应特征，其目的是揭示苏鲁超高压变质带的内部结构，以重塑超高压变质岩石的折返过程。
由于工区岩石类型多样、地质构造复杂、地层倾角大，围绕预先导孔和先导孔所进行的两次地震数据采集均采用了井地联合的观测方法，微测井则是按照三维逆VSP的观测方式进行的。VSP速度分析表明，苏鲁超高压变质岩的地震波速度介于4500-7000m／s之间，明显高于一般的沉积岩类岩石，而且随深度增加而增加的趋势不明显。研究认为，变质岩的地震波速度与变质作用类型和强度、岩石密度、岩性及构造有关，同时由于该区超高压变质岩的面状构造发育，而且不同地震波速度的岩石在空间上表现出明显的迭置关系，因此地震波速度呈现出显著的各向异性和横向不均匀性。根据微测井资料的处理结果，工区地壳表层由浅到深可依次划分为低速带、高降速带、低降速带和新鲜基岩四个带，是风化作用强度和工区岩石性质的综合反映。关于地震反射的原因，认为主要是韧性剪切带、岩性分界面和断层(破碎带)。通过地震反射剖面综合解释，查明了地震剖面上不同波组的地质意义，清晰地勾勒出韧性剪切带、榴辉岩体和断层在空间上的产出特征和展布规律。此外，利用地震资料中的倾角信息，对工区地层和构造的倾斜情况及空间变化作了分析。本文最后根据地质特征以及苏鲁超高压变质带的变质变形历史，结合地震资料提供的丰富深部信息，对苏鲁超高压变质带的折返机制进行了探讨。
Chinese Continental Scientific Drilling (CCSD) is a grand scientific project and received a worldwide attention. Maobei region of Donghai, Jiangsu, is selected as the CCSD site due to its specific tectonic position, large amount of ultra-high pressure metamorphic (UHPM) rocks and abundant information deep in the crust. Seismic response of the drilling site is discussed thoroughly in this paper on the basis of two seismic explorations, aiming at revealing the internal structure of Su-Lu UHPM belt and modeling returning process of UHPM rocks.
Since various rocks, complex structure and steep strata in the site, integrated well and ground seismic explorations were adopted on the two pilot holes, and 3D reverse VSP layout was used in microlog data acquiring. VSP velocity analysis shows that seismic velocities of the UHPM rocks, varying mainly from 4500 m/s to 7000m/s, are much higher than that of common sedimentary rocks and do not vary with their seated depth. It's considered that seismic velocity of metamorphic rock is related to metamorphic type and strength, density, Hthology and geologic structure, at the same time, intense foliation structure and interlayer of rocks different in velocity make seismic velocity present obvious anisotropy and transverse imhomogeneity. On the basis of microlog data, crustal surface layer in the site is divided from above to below into four belts: low-velocity belt, rapidly lowering belt, slowly lowerign belt and fresh bedrock, which embody both weathering strength and Hthology. With regard to the origin of seismic reflections, compositional contrasts, ductile shear zones and fractures are considered as the main cause. Comprehensive interpretation to seismic sections finds out geological implication of different wave groups and clearly sketch occurrence and distribution of ductile shear belt, eclogite body and fault. Moreover, dip information included in seismic files is used to analyze strata and structure dip and its variation in space. At the end, the returning mechanism of Su-Lu UHPM belt is discussed on the basis of geologic characteristics and its deforming-metamorphic history as well as abundant information deep in the crust provided by seismic files.
由于工区岩石类型多样、地质构造复杂、地层倾角大，围绕预先导孔和先导孔所进行的两次地震数据采集均采用了井地联合的观测方法，微测井则是按照三维逆VSP的观测方式进行的。VSP速度分析表明，苏鲁超高压变质岩的地震波速度介于4500-7000m／s之间，明显高于一般的沉积岩类岩石，而且随深度增加而增加的趋势不明显。研究认为，变质岩的地震波速度与变质作用类型和强度、岩石密度、岩性及构造有关，同时由于该区超高压变质岩的面状构造发育，而且不同地震波速度的岩石在空间上表现出明显的迭置关系，因此地震波速度呈现出显著的各向异性和横向不均匀性。根据微测井资料的处理结果，工区地壳表层由浅到深可依次划分为低速带、高降速带、低降速带和新鲜基岩四个带，是风化作用强度和工区岩石性质的综合反映。关于地震反射的原因，认为主要是韧性剪切带、岩性分界面和断层(破碎带)。通过地震反射剖面综合解释，查明了地震剖面上不同波组的地质意义，清晰地勾勒出韧性剪切带、榴辉岩体和断层在空间上的产出特征和展布规律。此外，利用地震资料中的倾角信息，对工区地层和构造的倾斜情况及空间变化作了分析。本文最后根据地质特征以及苏鲁超高压变质带的变质变形历史，结合地震资料提供的丰富深部信息，对苏鲁超高压变质带的折返机制进行了探讨。
Chinese Continental Scientific Drilling (CCSD) is a grand scientific project and received a worldwide attention. Maobei region of Donghai, Jiangsu, is selected as the CCSD site due to its specific tectonic position, large amount of ultra-high pressure metamorphic (UHPM) rocks and abundant information deep in the crust. Seismic response of the drilling site is discussed thoroughly in this paper on the basis of two seismic explorations, aiming at revealing the internal structure of Su-Lu UHPM belt and modeling returning process of UHPM rocks.
Since various rocks, complex structure and steep strata in the site, integrated well and ground seismic explorations were adopted on the two pilot holes, and 3D reverse VSP layout was used in microlog data acquiring. VSP velocity analysis shows that seismic velocities of the UHPM rocks, varying mainly from 4500 m/s to 7000m/s, are much higher than that of common sedimentary rocks and do not vary with their seated depth. It's considered that seismic velocity of metamorphic rock is related to metamorphic type and strength, density, Hthology and geologic structure, at the same time, intense foliation structure and interlayer of rocks different in velocity make seismic velocity present obvious anisotropy and transverse imhomogeneity. On the basis of microlog data, crustal surface layer in the site is divided from above to below into four belts: low-velocity belt, rapidly lowering belt, slowly lowerign belt and fresh bedrock, which embody both weathering strength and Hthology. With regard to the origin of seismic reflections, compositional contrasts, ductile shear zones and fractures are considered as the main cause. Comprehensive interpretation to seismic sections finds out geological implication of different wave groups and clearly sketch occurrence and distribution of ductile shear belt, eclogite body and fault. Moreover, dip information included in seismic files is used to analyze strata and structure dip and its variation in space. At the end, the returning mechanism of Su-Lu UHPM belt is discussed on the basis of geologic characteristics and its deforming-metamorphic history as well as abundant information deep in the crust provided by seismic files.
引文
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[8] 杨文采．后板块地球内部物理学导轮．北京：地质出版社，1999．
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[14] 杨文采，张春贺，朱光明．标定大陆科学钻探孔区地震反射体[J]．地球物理学报，2001，45(3)：370—384．
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[19] 姜修道，朱光明．变质岩区地震波速度的特点及其影响因素．地球物理学进展，2003．18(2)：331—335．
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[22] 姜修道，朱光明．苏鲁超高压变质带的地震响应特征．见：长安大学地质工程与测绘工程学院编。地球探测科学与技术新进展．北京：中国科学技术出版社，2002．
[23] 高山，金振民，H．Kern等．大别超高压榴辉岩高温高压下地震波速和密度的初步实验研究．科学通报，1997，42(8)：862—866．
[24] Christensen, N.I., Mooney, W.D.. Seismic velocity structure and composition of the continental crust: a global view[J]. J. GeoPhys. Res. 1995, 100: 9761-9788.
[25] Smithson, S.B.. Shive, P.N. Seismic velocity, reflections, and structure of the crystalline crust[J]. Am. Geophys. Union Geophys Monogr. 1977,20: 254-270.
[26] Smithson, S.B.. Johnson, R.A., Hurich, C.A. Crustal reflections and crustal structure. Reflect[J]. Seismol.: the Continental Crust Geodynam. Ser. 1986, 14: 21-32.
[27] Hurich, C.A., Smithson, S.B.. Compositional variation and the origin of deep crustal reflections[J]. Earth Planet. Sci. Lett. 1987, 85: 416-426.
[28] Smithson, S.B., Brewer, J.A., Kaufman, S., et. al. Structure of the Laramide Wind River uplift, Wyoming from COCORP deep reflection data and gravity data[J]. J. Geophys. Res. 1979, 84: 5955-5972.
[29] Hurich, C.A., Smithson, S.B., Fountain, D.M., et.al. Seismic evidence of mylonite reflectivity and deep structure in the Kettle Dome metamorphic core complex[J]. Washington Geology, 1985, 13: 577-580.
[30] Ewald L?schen, Kurt Bram, Walter S?llner, et.al. Nature of seismic reflections and velocities from VSP-experiments and borehole measurements at the KTB deep drilling site in southeast Germany[J]. Tectonophysics, 1996,264, 309-324.
[31] Deemer, S., Hurich, C.. Seismic images of the basal portion of the Bjerkreim-Sokndal layered intrusion[J]. Geology 1997, 25, 1107-1110.
[32] 姜修道，朱光明，朱龙生等．中国大陆科学钻探先导孔VSP资料解释．长安大学学报(地球科学版)，2004，26(1)
[33] Jones, T. D., Nur, A.. The nature of seismic reflections from deep crustal faults zones. J. Geophys. Res. 1984, 89, 3153-3171.
[34] McDonough, D. T., Fountain, D. M.. Reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples. Geophys. J. R. Astron. Soc. 1988, 93,547-558.
[35] Christensen, N.I.. Reflectivity and seismic properties of the deep continental crust. J. Geophys. Res. 1989, 94, 17793-17804.
[36] 中国大陆科学钻探中心地学部．三维地震与先导孔VSP子工程招标文件．2001．8
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[46] 索书田，钟增球，游振东．大别地块超高压变质期后伸展变形及超高压变质岩石折返过程．中国科学(D辑)，2000，1：9—17．
[2] Pakisr I. C, Mooney W D, eds. Geophysical Framework of the Continental United States. Geol. Soc. Am. MeMoir 172, 1999.
[3] Clowes R, Cook F, Hajnal Z, et al. Canada's LITHOPROBE project. Episodes. 1999,22 (1): 3-20.
[4] Teng Jiwen, Xiong Shaohai, Zhang Zhongjie, et al. Deep structure pattern, anisotropy and continental geodynamics revealed by geophysical profiles and transects in China. In: Liu Guangding ed. Proc. 30th international Geological Congress: Geophysics, Vol. 20 Utrecht, Netherlands: VSP, 1997, 21-40.
[5] 张永康．江苏东海——中国第一口大陆科学钻探的最佳选区之一．江苏地质，1997，21(3)：129—137．
[6] 索书田，钟增球，游振东．大别地块超高压变质期后伸展变形及超高压变质岩石折返过程[J]．中国科学(D辑)，2000，30(1)：9—17．
[7] 索书田，钟增球，游振东．大别—苏鲁超高压变质带内变形分解作用对榴辉岩透镜体群发育的影响．地质科技情报，2001，20(2)：15—22．
[8] 杨文采．后板块地球内部物理学导轮．北京：地质出版社，1999．
[9] 索书田，钟增球，周汉文．苏北东海地区超高压变质带内的斜卧褶皱．地质科技情报，2002，(2)：1—7．
[10] 西安工程学院应用物理研究所．苏北东海县毛北大陆科学钻探孔区地球物理调查研究—垂直地震剖面调查研究(科研报告)．1999．
[11] 杜邦公司编；龙维祺等译．爆破手册．北京：冶金工业出版社，1986．
[12] 余钦范，郭友钊，孟小红等．苏北大陆科学钻探靶区岩石物理性质．地球物理学报，2002．45(1)：93—100．
[13] S.B. Smithson, F. Wenzel, Y.V. Ganchin, et. al. Seismic results at Kola and KTB deep scientific borehole: velocities, reflections, fluids, and crustal composition[J]. Tectonophysics, 2000,329:301-317.
[14] 杨文采，张春贺，朱光明．标定大陆科学钻探孔区地震反射体[J]．地球物理学报，2001，45(3)：370—384．
[15] 董敏煜．地震勘探．北京：石油大学出版社，2000．
[16] 何樵登．地震勘探原理和方法．北京：地质出版社，1985．
[17] R．E．谢里夫，L．P．吉尔达特编；初英，李承楚，王宏伟等译．勘探地震学(第二版)．北京：石油工业出版社，1999．
[18] 周绪文编．反射波地震勘探方法．北京：石油工业出版社，1989．
[19] 姜修道，朱光明．变质岩区地震波速度的特点及其影响因素．地球物理学进展，2003．18(2)：331—335．
[20] 贺同兴，卢良兆，李树勋等．变质岩岩石学．北京：地质出版社，1980．
[21] Jones, T. D., Nur, A., 1984. The nature of seismic reflections from deep crustal faults zones. J. Geophys. Res.89,3153-3171.
[22] 姜修道，朱光明．苏鲁超高压变质带的地震响应特征．见：长安大学地质工程与测绘工程学院编。地球探测科学与技术新进展．北京：中国科学技术出版社，2002．
[23] 高山，金振民，H．Kern等．大别超高压榴辉岩高温高压下地震波速和密度的初步实验研究．科学通报，1997，42(8)：862—866．
[24] Christensen, N.I., Mooney, W.D.. Seismic velocity structure and composition of the continental crust: a global view[J]. J. GeoPhys. Res. 1995, 100: 9761-9788.
[25] Smithson, S.B.. Shive, P.N. Seismic velocity, reflections, and structure of the crystalline crust[J]. Am. Geophys. Union Geophys Monogr. 1977,20: 254-270.
[26] Smithson, S.B.. Johnson, R.A., Hurich, C.A. Crustal reflections and crustal structure. Reflect[J]. Seismol.: the Continental Crust Geodynam. Ser. 1986, 14: 21-32.
[27] Hurich, C.A., Smithson, S.B.. Compositional variation and the origin of deep crustal reflections[J]. Earth Planet. Sci. Lett. 1987, 85: 416-426.
[28] Smithson, S.B., Brewer, J.A., Kaufman, S., et. al. Structure of the Laramide Wind River uplift, Wyoming from COCORP deep reflection data and gravity data[J]. J. Geophys. Res. 1979, 84: 5955-5972.
[29] Hurich, C.A., Smithson, S.B., Fountain, D.M., et.al. Seismic evidence of mylonite reflectivity and deep structure in the Kettle Dome metamorphic core complex[J]. Washington Geology, 1985, 13: 577-580.
[30] Ewald L?schen, Kurt Bram, Walter S?llner, et.al. Nature of seismic reflections and velocities from VSP-experiments and borehole measurements at the KTB deep drilling site in southeast Germany[J]. Tectonophysics, 1996,264, 309-324.
[31] Deemer, S., Hurich, C.. Seismic images of the basal portion of the Bjerkreim-Sokndal layered intrusion[J]. Geology 1997, 25, 1107-1110.
[32] 姜修道，朱光明，朱龙生等．中国大陆科学钻探先导孔VSP资料解释．长安大学学报(地球科学版)，2004，26(1)
[33] Jones, T. D., Nur, A.. The nature of seismic reflections from deep crustal faults zones. J. Geophys. Res. 1984, 89, 3153-3171.
[34] McDonough, D. T., Fountain, D. M.. Reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples. Geophys. J. R. Astron. Soc. 1988, 93,547-558.
[35] Christensen, N.I.. Reflectivity and seismic properties of the deep continental crust. J. Geophys. Res. 1989, 94, 17793-17804.
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