帕米尔—兴都库什地区板块俯冲及其应力状态
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摘要
利用美国国家地震信息中心(NEIC)提供的1973—2006年地震目录、哈佛大学提供的1978—2005年地震机制解资料,精细地研究了帕米尔—兴都库什地区印度板块与欧亚板块的碰撞形态,分析了地震震源机制特征。研究结果认为:欧亚板块以约50°的倾角向南俯冲,地震最大深度为364km;印度板块以层间插入的方式与欧亚板块碰撞,在帕米尔"结"附近碰撞强烈,地震活动明显增强,震源剖面显示"V"字型分布形态;在帕米尔"结"两侧,随着印度板块俯冲动力减弱,地震活动也明显减弱,地震震源剖面显示,印度板块向北俯冲的剖面形态逐渐消失,欧亚板块向SE俯冲的剖面形态越加清晰,从地震震源剖面分布形态分析,印度板块没有穿过欧亚板块,印度板块向北的反复、多期的叠瓦式地震分布形态,可能反映印度板块向北俯冲→断离、再俯冲→再断离的过程。由于印度板块与欧亚板块间的强烈碰撞挤压作用,帕米尔—兴都库什地区处于以近SN向的挤压构造应力状态,逆断层数量约占70%,正断层数量约占11%,走滑断层数量约占19%。P轴优势方位显示帕米尔—兴都库什地区主压应力近SN向,倾角近水平,呈现由南向北倾斜;T轴倾角近垂直,整体接近俯冲带的倾向。帕米尔—兴都库什地区应力场特征表明,印度板块向北的主动推挤,是形成这一区域应力场的主动力,向南倾的欧亚板块处于一种被动的被挤压状态。
In this paper,the collision configuration between Indian plate and Eurasian plate was studied in detail and the focal mechanism solutions of the earthquakes were analyzed by using the earthquake catalogues from 1973 to 2006 provided by NEIC and focal mechanism solutions from 1978 to 2005 provided by Harvard University.The results indicate that:Eurasian plate was underthrust southwards with a dip of 50°,and the maximum focal depth is 364km;Indian plate collided with Eurasian plate by means of interlayer intercalation.The collision was strong among the Pamir knot,where the seismic activities were enhanced significantly.The focal profile shows a "V-shape" distribution;on the sides of the Pamir knot,the seismic activities decreased apparently along with the decreasing subduction force of the Indian plate.The focal profile indicates that the profile configuration of the northward-subduction of the Indian plate disappeared gradually and the profile configuration of the southeastward-subduction of the Eurasian plate is more perspicuous.The analysis on the distribution pattern of the focal profile suggests that the Indian plate did not penetrate the Eurasian plate.The repeated multi-period and imbricate distribution of earthquake may be the reflection of the process of northward-subduction,detachment,and then re-subduction and re-detachment of the Indian plate.As a result of strong collision and extrusion between Indian plate and Eurasian plate,Pamir-Hindukush region is under a tectonic stress state of near-NS compression.The number of reverse faults accounts for about 70%of the total,the normal faults account for about 11%,and the strike-slip faults,about 19%.The predominant orientation of P axis indicates that the principal compressive stress is oriented near-NS,the dip is near-horizontal,inclining from south to north;and the dip of T axis is near-vertical,similar to the dip of subduction zone.Characteristics of stress field in Pamir-Hindukush show that the active northward-extrusion of Indian plate is the main dynamics of the regional stress field,and the Eurasian plate which dips southward is in a state of passive extrusion.
In this paper,the collision configuration between Indian plate and Eurasian plate was studied in detail and the focal mechanism solutions of the earthquakes were analyzed by using the earthquake catalogues from 1973 to 2006 provided by NEIC and focal mechanism solutions from 1978 to 2005 provided by Harvard University.The results indicate that:Eurasian plate was underthrust southwards with a dip of 50°,and the maximum focal depth is 364km;Indian plate collided with Eurasian plate by means of interlayer intercalation.The collision was strong among the Pamir knot,where the seismic activities were enhanced significantly.The focal profile shows a "V-shape" distribution;on the sides of the Pamir knot,the seismic activities decreased apparently along with the decreasing subduction force of the Indian plate.The focal profile indicates that the profile configuration of the northward-subduction of the Indian plate disappeared gradually and the profile configuration of the southeastward-subduction of the Eurasian plate is more perspicuous.The analysis on the distribution pattern of the focal profile suggests that the Indian plate did not penetrate the Eurasian plate.The repeated multi-period and imbricate distribution of earthquake may be the reflection of the process of northward-subduction,detachment,and then re-subduction and re-detachment of the Indian plate.As a result of strong collision and extrusion between Indian plate and Eurasian plate,Pamir-Hindukush region is under a tectonic stress state of near-NS compression.The number of reverse faults accounts for about 70%of the total,the normal faults account for about 11%,and the strike-slip faults,about 19%.The predominant orientation of P axis indicates that the principal compressive stress is oriented near-NS,the dip is near-horizontal,inclining from south to north;and the dip of T axis is near-vertical,similar to the dip of subduction zone.Characteristics of stress field in Pamir-Hindukush show that the active northward-extrusion of Indian plate is the main dynamics of the regional stress field,and the Eurasian plate which dips southward is in a state of passive extrusion.
引文
雷建设,周蕙兰,赵大鹏.2002.帕米尔及邻近地区地壳上地幔P波三维速度结构的研究[J].地球物理学报,45(6):802—811.LEI Jian-she,ZHOU Hui-lan,ZHAO Da-peng.2002.3-D velocity structure of P wave in the crust and upper mantle be-neath Pamir and adjacent region[J].Chinese J Geophys,45(6):802—811(in Chinese).
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张家声,单新建,李建华.2005.帕米尔地区现今大陆深俯冲:地震构造和动力学解释[J].岩石学报,21(4):1215—1227.ZHANG Jia-sheng,SHAN Xin-jian,LI Jian-hua.2005.Recent deep subducting of continental crust in Pamier:An in-terpretation on seismotectonics and geodynamics[J].Acta Petrologica Sinica,21(4):1215—1227(in Chinese).
赵文津,薛光琦,吴珍汉,等.2004.西藏高原上地幔的精细结构与构造:地震层析成像给出的启示[J].地球物理学报,47(2):449—455.ZHAO Wen-jin,XUE Guang-qi,WUZhen-han,et al.2004.Fine velocity structure of the upper mantle beneath the Xi-zang Plateau from tomography and its geological interpretations[J].Chinese J Geophys,47(2):449—455(inChinese).
赵俊猛,李纯植,马宗晋.2003.天山分段性的地球物理学分析[J].地学前缘,10(特刊):125—131.ZHAO Jun-meng,LI Chun-zhi,MAZong-jin.2003.Geophysical evidence segmentation of the Tianshan[J].Earth Sci-ence Frontiers,10(Special issue):125—131(in Chinese).
Burtman V S,Molnar P.1993.Geological and Geophysical Evidence for Deep Subduction of Continental Crust beneaththe Pamir[M].Colorado:The Geological Society of America.
宁杰远,臧绍先.1990.帕米尔—兴都库什地区地震空间分布特征及应力场特征[J].地球物理学报,33(6):657—669.NING Jie-yuan,ZANG Shao-xian.1990.The distribution of earthquakes and stress state in Pamir-Hindukush regiongs[J].Chinese J Geophys,33(6):657—669(in Chinese).
孙文斌,和跃时.2004.西太平洋Benioff带的形态及其应力状态[J].地球物理学报,47(3):433—440.SUN Wen-bin,HE Yue-shi.2004.Characteristics of the subduction zone in the western Pacific and its stress state[J].Chinese J Geophys,47(3):433—440(in Chinese).
任金卫,马宗晋.2003.东亚地区现代地壳运动特征与构造变形[J].地学前缘,10(特刊):58—65.REN Jin-wei,MAZong-jin.2003.Crustal movement and tectonic deformation of eastern Asia[J].Earth Science Fron-tiers,10(Special issue):58—65(in Chinese).
谢富仁,崔效锋,赵建涛.2003.全球应力场与构造分析[J].地学前缘,10(特刊):22—30.XIE Fu-ren,CUI Xiao-feng,ZHAO Jian-tao.2003.Analysis of global tectonic stress field[J].Earth Science Fron-tiers,10(Special issue):22—30(in Chinese).
张家声,单新建,李建华.2005.帕米尔地区现今大陆深俯冲:地震构造和动力学解释[J].岩石学报,21(4):1215—1227.ZHANG Jia-sheng,SHAN Xin-jian,LI Jian-hua.2005.Recent deep subducting of continental crust in Pamier:An in-terpretation on seismotectonics and geodynamics[J].Acta Petrologica Sinica,21(4):1215—1227(in Chinese).
赵文津,薛光琦,吴珍汉,等.2004.西藏高原上地幔的精细结构与构造:地震层析成像给出的启示[J].地球物理学报,47(2):449—455.ZHAO Wen-jin,XUE Guang-qi,WUZhen-han,et al.2004.Fine velocity structure of the upper mantle beneath the Xi-zang Plateau from tomography and its geological interpretations[J].Chinese J Geophys,47(2):449—455(inChinese).
赵俊猛,李纯植,马宗晋.2003.天山分段性的地球物理学分析[J].地学前缘,10(特刊):125—131.ZHAO Jun-meng,LI Chun-zhi,MAZong-jin.2003.Geophysical evidence segmentation of the Tianshan[J].Earth Sci-ence Frontiers,10(Special issue):125—131(in Chinese).
Burtman V S,Molnar P.1993.Geological and Geophysical Evidence for Deep Subduction of Continental Crust beneaththe Pamir[M].Colorado:The Geological Society of America.
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