浅层地震在永冻区探测冻土层厚度的试验研究  

An experimental study of the capability of shallow seismic method in detecting the frozen soil thickness in permafrost region

作　　者：徐建宇[1,2] 姜春香 岳航羽[1,2] 王凯 

机构地区：[1]中国地质科学院地球物理地球化学勘查研究所,河北廊坊065000 [2]国家现代地质勘查工程技术研究中心,河北廊坊065000 [3]吉林大学地球探测科学与技术学院,吉林长春130026

出　　处：《物探与化探》2017年第6期1121-1126,共6页Geophysical and Geochemical Exploration

基　　金：国家高技术研究发展计划("863"计划)课题"冻土带天然气水合物地球物理勘查技术"(2012AA061403);中国地质调查局地质调查项目"羌塘盆地天然气水合物资源勘查(浅层高分辨率反射地震测量)"(GZHL20110305);"陆域天然气水合物勘查技术研究与集成"(GZHL20110324)

摘　　要：作为陆域永冻土区天然气水合物矿藏的盖层,天然气水合物的分布与冻土层密切相关。利用地震方法探测冻土层是该方法寻找天然气水合物的新尝试。青藏高原永冻土区冻土厚度相对较薄,为有效地探测冻土层,需采用小道间距、小炮间距、小偏移距和高覆盖次数的反射地震方法技术。由于松散沉积地层冻结前后的速度差别较大,利用地震速度谱和冻土底界反射波能够可靠地探测冻土层的厚度。对于孔隙度较低的硬岩沉积地层,虽冻结前后的地层速度差别相对较小,但冻结层底界面上下地层的波阻抗差异也会因冻结层的存在使正常反射波组在冻结层底界处出现不连续和扰动,依据地震速度谱和倾斜地层反射波组的扰动不连续可解释冻土层厚度。As the cover of natural gas hydrate deposits in terrestrial permafrost region, the distribution of natural gas hydrate is closely related to the permafrost.h is a new attempt to find the natural gas hydrate by means of seismic method.In order to detect frozen soil ef- fectively, the authors used the method of seismic reflection with small group distance, small shot interval, small offset and high coverage because the permafrost thickness is relatively thin in permafrost region of the Tibetan Plateau. Due to the large difference between the velocities of unconsolidated sedimentary strata with and without freezing, the thickness of frozen soil layer can be reliably detected by analyzing seismic velocity spectrum and reflections reformed by frozen bottom interface.Although the velocity difference of the strata with and without freezing is relatively small for low porosity hard rock sedimentary strata, the impedance difference between the upper and lower strata of the frozen bottom interface will cause the normal reflections to be disturbed and discontinuous.The thickness of the hard rock sedimentary frozen strata can be explained according to the seismic velocity spectrum and the discontinuous disturbance of the tilted reflections.

关 键 词：永冻土盖层 松散沉积地层 硬岩沉积地层 天然气水合物 反射地震 速度谱 

分 类 号：P631.4[天文地球—地质矿产勘探]