帕米尔-兴都库什地区的板块俯冲特征
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摘要
本文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,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,分析了印度板块向北俯冲对地震活动及其区域应力场的影响。地震震源三维图象显示:欧亚板块与印度板块在帕米尔"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"东侧,随着印度板块俯冲动力减弱,地震活动也明显减弱,印度板块向北俯冲的剖面形态逐渐消失,欧亚板块向东南俯冲的剖面形态越加清晰;印度板块向北俯冲具有由浅向深、由南向北反复迁移的特征,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南北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南北向,倾角近水平,呈现由南向北倾斜;T轴倾角较大,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。
Based on earthquake catalogues from 1973 to 2006 provided by NEIC and focal mechanism solutions from 1978 to 2005 provided by Harvard University.,this paper researched the collision forms between Pamir-Hindukushi region and Eurasian plate,and analyzed Indian plate towards north subduction affect seismic active and the local stress field.The 3-d earthquake focal image showed that Eurasian plate and Indian plate created strong collision near the Pamir "node".The seismic activity obviously increased.The focal section was distributed of "V" form;On Pamir "node" eastern,with subduction force of Indian plate weaken.The earthquake activity also obviously decreased.The section form of Indian plate which dived towards north gradually disappeared.The section form of Eurasian plate towards southeast subduction became more clear.Indian plate which dived towards north repeatedly moved from shallow to deep,and from south to north.This character maybe reflect the procedure that Indian plateclived towards north and broken,re-subduction and re-broken.As the strong collision and extrusion between Indian plate and Eurasian plate,Pamir-Hindukush region was in a stress state of nearly NS-trending extrusion structure.The number of reverse faults accounted for about 70%.Normal faults accounted for about 11%.And strike-slip faults accounted for about 19%.P axis advantage trend showed that principal compressive stress was nearly NS-trending,the dip was nearly Horizontal which inclined from south to north.And the dip of T axis was nearly vertical which was close to the dip of subduction zone.Characteristics of stress field in Pamir-Hindukush showed that the northward activity broaching of Indian plate was the main power which formed the regional stress field.And the Eurasian plate which inclined southward was in a status of passive extrusion.
Based on earthquake catalogues from 1973 to 2006 provided by NEIC and focal mechanism solutions from 1978 to 2005 provided by Harvard University.,this paper researched the collision forms between Pamir-Hindukushi region and Eurasian plate,and analyzed Indian plate towards north subduction affect seismic active and the local stress field.The 3-d earthquake focal image showed that Eurasian plate and Indian plate created strong collision near the Pamir "node".The seismic activity obviously increased.The focal section was distributed of "V" form;On Pamir "node" eastern,with subduction force of Indian plate weaken.The earthquake activity also obviously decreased.The section form of Indian plate which dived towards north gradually disappeared.The section form of Eurasian plate towards southeast subduction became more clear.Indian plate which dived towards north repeatedly moved from shallow to deep,and from south to north.This character maybe reflect the procedure that Indian plateclived towards north and broken,re-subduction and re-broken.As the strong collision and extrusion between Indian plate and Eurasian plate,Pamir-Hindukush region was in a stress state of nearly NS-trending extrusion structure.The number of reverse faults accounted for about 70%.Normal faults accounted for about 11%.And strike-slip faults accounted for about 19%.P axis advantage trend showed that principal compressive stress was nearly NS-trending,the dip was nearly Horizontal which inclined from south to north.And the dip of T axis was nearly vertical which was close to the dip of subduction zone.Characteristics of stress field in Pamir-Hindukush showed that the northward activity broaching of Indian plate was the main power which formed the regional stress field.And the Eurasian plate which inclined southward was in a status of passive extrusion.
引文
[1]赵俊猛,李纯植,马宗晋.天山分段性的地球物理学分析[J].地学前缘.2003.10[特刊]:125-131.
[2]BURTMAN V S,MOLNAR P.Geological and GeophysicalEvidence for Deep Subduction of Continental Crust Beneath the Pamir[M].1993.Colorado:The Geological Society of America
[3]雷建设,周蕙兰,赵大鹏.帕米尔及临近地区地壳上地幔P波三维速度结构的研究[J].地球物理学报.2002.45(6):802-811.
[4]宁杰远,臧绍先.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.1990.33(6):657-669.
[5]孙文斌,和跃时,常征等.帕米尔-兴都库什地区板块俯冲及其应力状态[J].地震地质.2009.31(2):207-217
[6]任金卫,马宗晋.东亚地区现代地壳运动特征与构造变形[J].地学前缘.2003.10[特刊]:58-65.
[7]张家声,单新建,李建华.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.2005.21(4):1215-1227.
[8]谢富仁,崔效锋,赵建涛.全球应力场与构造分析[J].地学前缘.2003.10[特刊]:22-30.
[2]BURTMAN V S,MOLNAR P.Geological and GeophysicalEvidence for Deep Subduction of Continental Crust Beneath the Pamir[M].1993.Colorado:The Geological Society of America
[3]雷建设,周蕙兰,赵大鹏.帕米尔及临近地区地壳上地幔P波三维速度结构的研究[J].地球物理学报.2002.45(6):802-811.
[4]宁杰远,臧绍先.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.1990.33(6):657-669.
[5]孙文斌,和跃时,常征等.帕米尔-兴都库什地区板块俯冲及其应力状态[J].地震地质.2009.31(2):207-217
[6]任金卫,马宗晋.东亚地区现代地壳运动特征与构造变形[J].地学前缘.2003.10[特刊]:58-65.
[7]张家声,单新建,李建华.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.2005.21(4):1215-1227.
[8]谢富仁,崔效锋,赵建涛.全球应力场与构造分析[J].地学前缘.2003.10[特刊]:22-30.
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