中国大陆科学探井岩性的VSP地震特征分析
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摘要
中国大陆科学钻探(CCSD)井位于苏鲁超高压变质带南部,地处郯庐断裂东侧的东海县境内。VSP地震勘探为CCSD多学科研究内容之一,利用数字地震仪(HF300)和多级三分量数字检波器(GeoChain)对探井进行了VSP测量。结合VSP勘探结果和CCSD探井5000 m岩性资料,分析了井中岩性分段特征、超高压变质岩的地震响应特征和vp/vs比值特征,取得了若干具有科学意义的结论:(1)以榴辉岩的分布和组合特征进行的岩性分段比较合理,每段的VSP速度和测井密度等特征和岩性分布具有很好的一致性。(2)榴辉岩与片麻岩界面以及剪切带均可形成强反射,正/副片麻岩界面也可产生明显反射,透镜状和条带状岩体的反射同相轴呈现不同程度的弯曲,剪切带的反射同相轴连续性好。(3)榴辉岩以高波速(6.3 km/s)、低vp/vs值(1.2)和波组强而稀疏为特征,副片麻岩以较高波速(6.1 km/s)、高vp/vs值(1.8)和波组较稀疏为特征,正片麻岩以较低波速(5.8 km/s)、中等vp/vs值(1.5)和波组较密集为特征,而剪切带以强反射、vp/vs值最高(2.2)为特征,而且不论剪切带出现在哪种岩性中其vp/vs值都很高。该研究成果不但揭示了变质带的地震响应特征,同时为二维或三维地面地震解释提供科学依据,减少解释分析中的多解性和不确定性,能够有效地提高中国大陆科学钻探孔区地质构造解释的可信度,为其他学科研究提供依据。
The main hole of Chinese Continental Scientific Drilling(CCSD) is located at Donghai County which is in the eastern side of the Tanlu fault and is at the southern part of Sulu ultra-high pressure metamorphic belt.The VSP survey is one part of the multi-scientific research.The hole has been surveyed by employing digital seismic instrument(HF300) and digital three-component geophone technique(GeoChain).Combining the VSP surveying results and the 5,000-meter lithologic characteristics of the hole,the features of lithology grouping,seismic responses of ultrahigh-pressure metamorphic rocks,and the relationship between vp/vs and lithology have been analyzed,it comes to a conclusion that:(1) it is advisable that metamorphic rock is grouped by the characteristics of distribution and association of eclogites,because the VSP velocities match well with logging density and lithology distribution in each group;(2) all the eclogite-gneiss interfaces and the shear zones can generate strong reflections,the orthogneiss-paragneiss interfaces can form obvious reflections,and sometimes the reflection events of lending or banded rocks are bending,while the reflection events of shear zones are continuous;and(3)the eclogites are characterized with high velocity(6.3 km/s),low vp/vs ratio(1.2),and strong and sparse wave trains,while the paragneisses with middle velocity(6.1 km/s) and high vp/vs ratio(1.8) and sparse wave trains,the orthogneisses with low velocity(5.8 km/s) and middle vp/vs ratio(1.5) and dense wave trains;and the shear zones have the characteristics of the strong reflections and the highest vp/vs ratio(2.2),the vp/vs ratio of shear zones is high,no matter what kind of rocks they emerge in.The research results can not only discover the seismic responses of ultrahigh-pressure metamorphic rocks,but also and more significantly,provide evidences for 2D or 3D surface seismic interpretation,decrease the ambiguity and uncertainty of interpretation,enhance the reliability of geological structure interpretation in CCSD region.
The main hole of Chinese Continental Scientific Drilling(CCSD) is located at Donghai County which is in the eastern side of the Tanlu fault and is at the southern part of Sulu ultra-high pressure metamorphic belt.The VSP survey is one part of the multi-scientific research.The hole has been surveyed by employing digital seismic instrument(HF300) and digital three-component geophone technique(GeoChain).Combining the VSP surveying results and the 5,000-meter lithologic characteristics of the hole,the features of lithology grouping,seismic responses of ultrahigh-pressure metamorphic rocks,and the relationship between vp/vs and lithology have been analyzed,it comes to a conclusion that:(1) it is advisable that metamorphic rock is grouped by the characteristics of distribution and association of eclogites,because the VSP velocities match well with logging density and lithology distribution in each group;(2) all the eclogite-gneiss interfaces and the shear zones can generate strong reflections,the orthogneiss-paragneiss interfaces can form obvious reflections,and sometimes the reflection events of lending or banded rocks are bending,while the reflection events of shear zones are continuous;and(3)the eclogites are characterized with high velocity(6.3 km/s),low vp/vs ratio(1.2),and strong and sparse wave trains,while the paragneisses with middle velocity(6.1 km/s) and high vp/vs ratio(1.8) and sparse wave trains,the orthogneisses with low velocity(5.8 km/s) and middle vp/vs ratio(1.5) and dense wave trains;and the shear zones have the characteristics of the strong reflections and the highest vp/vs ratio(2.2),the vp/vs ratio of shear zones is high,no matter what kind of rocks they emerge in.The research results can not only discover the seismic responses of ultrahigh-pressure metamorphic rocks,but also and more significantly,provide evidences for 2D or 3D surface seismic interpretation,decrease the ambiguity and uncertainty of interpretation,enhance the reliability of geological structure interpretation in CCSD region.
引文
[1]杨文采.后板块地球内部物理学导论[M].北京:地质出版社,1999:1-142.
[2]许志琴,张泽明,刘福来,等.中国大陆科学钻探主孔1200米构造柱及变形构造初步解析[J].岩石学报,2004,20(1):53-72.
[3]杨文采,杨午阳,程振炎.中国大陆科学钻探区三维地震资料的初步解释[J].岩石学报,2004,20(1):127-138.
[4]长安大学应用地球物理研究所.中国大陆科学钻探工程先导孔地震调查VSP子工程总结报告[R].西安:长安大学,2002.
[2]许志琴,张泽明,刘福来,等.中国大陆科学钻探主孔1200米构造柱及变形构造初步解析[J].岩石学报,2004,20(1):53-72.
[3]杨文采,杨午阳,程振炎.中国大陆科学钻探区三维地震资料的初步解释[J].岩石学报,2004,20(1):127-138.
[4]长安大学应用地球物理研究所.中国大陆科学钻探工程先导孔地震调查VSP子工程总结报告[R].西安:长安大学,2002.
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