龙门山及邻区重、磁异常特征及与地震关系的研究
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摘要
本文通过研究龙门山构造带及邻区的区域重、磁场特征,以及龙门山断裂带的产状等特征,探讨其与地震关系.研究结果表明,龙门山断裂带是环绕青藏高原的重力梯度带的一部分.其对应密度分界面向西北方向倾斜,向下延深数十公里,切穿莫霍面.推测密度分界面分为两段,深部较陡的为岩石圈块体的边界,浅部较缓.基底隆起与凹陷的界线大体与大地构造单元的界线一致.由西部的岩石圈块体的边界至东部在地表的大地构造单元界线之间的距离约为40-50 km.隶属于中上地壳脆性变形层的地质体由岩石圈块体界线沿缓倾的密度界面推覆至地表的大地构造单元的界线处,在此过程中伴随岩层破碎,从而发生地震.龙门山构造带主要部分位于负磁异常区,这种反磁化和退磁的现象,可能与逆冲推覆作用所引起的深部岩层倒转有关.
The gravity gradient belt in the Longmenshan fault zone is part of the great gravitygradient belt surrounding the Tibetan plateau in the north and the east. The density boundary plane, corresponding to the gravity gradient belt, exists beneath the surface. Based on seismic data, the immense boundary plane of density distribution might be extended downward several ten kilometers across the Moho. According to analysis for the Wenchuan earthquake and aftershocks, most of the earthquakes occurred in the upper and middle crust. Therefore, we suggest that the immense boundary plane of density distribution might be divided into two parts in depth. The deeper part in the westernmost of the Longmenshan fault zone is the boundary of lithosphere blocks, which dips steeply toward northwest. In contrast the shallower part located in the upper and middle crust and dips gently northwest. The boundary of the shallower part at the surface coincides roughly with the Anxian-Guanxian fault, the easternmost one of the Longmenshan fault system. The distance is about 40-50 km between the boundary of lithosphere block and the Anxian-Guanxian fault. When brittle part of the continental block move along the density boundary surfaces from boundary of lithosphere block to the tectonic boundary on the surface and rupture, earthquake will occur. The area around the Qingchuan-Wenchuan-Dujiangyan exhibits negative magnetic anomalies. Thrust faulting resulted in the overturn of the strata, which in turn caused reversal magnetization.
The gravity gradient belt in the Longmenshan fault zone is part of the great gravitygradient belt surrounding the Tibetan plateau in the north and the east. The density boundary plane, corresponding to the gravity gradient belt, exists beneath the surface. Based on seismic data, the immense boundary plane of density distribution might be extended downward several ten kilometers across the Moho. According to analysis for the Wenchuan earthquake and aftershocks, most of the earthquakes occurred in the upper and middle crust. Therefore, we suggest that the immense boundary plane of density distribution might be divided into two parts in depth. The deeper part in the westernmost of the Longmenshan fault zone is the boundary of lithosphere blocks, which dips steeply toward northwest. In contrast the shallower part located in the upper and middle crust and dips gently northwest. The boundary of the shallower part at the surface coincides roughly with the Anxian-Guanxian fault, the easternmost one of the Longmenshan fault system. The distance is about 40-50 km between the boundary of lithosphere block and the Anxian-Guanxian fault. When brittle part of the continental block move along the density boundary surfaces from boundary of lithosphere block to the tectonic boundary on the surface and rupture, earthquake will occur. The area around the Qingchuan-Wenchuan-Dujiangyan exhibits negative magnetic anomalies. Thrust faulting resulted in the overturn of the strata, which in turn caused reversal magnetization.
引文
2) 孙文珂,涂承林,金宜声.中国及毗邻海区布格重力异常图(1:500万),1999
[1] 许志琴,李化启,侯立炜等.青藏高原东缘龙门-锦屏造山带的崛起--大型拆离断层和挤出机制.地质通报,2007,26(10) :1262-1267 Xu Z Q, Li H Q, Hou L W,et al. Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau:Large-scale detachment faulting and extrusion mechanism. Geological Bulletin of China ( in Chinese) , 2007,26(10) :1262-1276
[2] 四川省地质矿产局.四川省区域地质志.中华人民共和国地质矿产部地质专报,一区域地质,第23号.北京:地质出版社,1982 Bureau of Geology and Mineral Resources of Sichuan Province. Regional geology of Sichuan province, People s Republic of China, Ministry of Geology and Mineral Resources, Geological Memoirs, Series 1, Number 23 (in Chinese). Beijing: Geological Publishing House, 1982
[3] 宋鸿彪,刘树根.龙门山中北段重磁场特征与深部构造关系.成都地质学院学报,1991,18(1) :74-82 Song H B, Liu S G. The relation of gravity and aeromagnetic field and deep structure in middle-northern Longmenshan mountains. Journal of Chengdu College of Geology (in Chinese), 1991,18(1) :74-82
[4] 宋鸿彪.龙门山造山带地质和地球物理资料的综合解释.成都地质学院学报,1994,21(2) :79-87 Song H B. The comprehensive interpretation of geological and geophysical data in the orogenic belt of Longmen mountains. Journal of Chengdu College of Geology (in Chinese), 1994, 21(2) :79-87
[5] 王懋基.黑水-泉州地学断面的重磁解释.地球物理学报,1994,37(3) :321-329 Wang M J. Gravity and magnetic interpretation of Heishui-Quanzhou geoscience transect. Chinese J. Geophys. (in Chinese), 1994,37(3) :321-329
[6] 钟锴,徐鸣洁,王良书等.川滇地区重力场特征与地壳变形研究.高校地质学报,2005,11(1) :111-117 Zhong K, Xu M J, Wang L S, et al. Study on characteristics of gravity field and crustal deformation in Sichuan-Yunnan region. Geological Journal of China Universities (in Chinese), 2005,11(1) :111-117
[7] Frey H. MAGSAT scale anomaly distribution: the global perspective. Geophys. Res. Lett. ,1982,9(6) ,277-280
[8] Press W H, Teukolsky S A, Vetterling W T, et al. Numerical Recipes in Fortran 77． The Art of Scientific Computing, Second Edition, Cambridge University Press,1992
[9] Hornby P, Boschetti F, Horowitz F G. Analysis of potential field data in the wavelet domain. Geophys. J. Int. , 1999,137:175-196
[10] 崔作舟,陈纪平,吴苓.花石峡-邵阳深部地壳结构和构造.中华人民共和国地质矿产部地质专报,五构造地质、地质力学,第21号.北京:地质出版社,1996 Cui Z Z, Chen J P, Wu L. Texture and structure of Huashixia-Shaoyang deep crust, People s Republic of China, Ministry of Geology and Mineral Resources, Geological Memoirs, Series 5, Number 21 (in Chinese). Beijing: Geological Publishing House, 1996
[11] 朱介寿.汶川地震的岩石圈深部结构与动力学背景.成都理工大学学报(自然科学版),2008,35(4) :348-356 Zhu J S. The Wenchuan earthquake occurrence background in deep structure and dynamics of lithosphere. Journal of Chengdu University of Technology Cin Chinese), 2008, 35 (4) :348-356
[12] 贾东,陈竹新,贾承造等.龙门山前陆褶皱冲断带构造解析与川西前陆盆地的发育.高校地质学报,2003,9:402-410 Jia D, Chen Z X, Jia C Z, et al. Structural features of the Longmen Shan fold and thrust belt and development of the western Sichuan foreland basin, central China. Geological Journal of China Universities (in Chinese), 2003,9:402-410
[13] 王有学,Mooney W D,韩国花等.台湾-阿尔泰地学断面阿尔金龙门山剖面的地壳纵波速度结构.地球物理学报,2005,48(1) :98-106 Wang Y X, Mooney W D, Han G H, et al. Crustal P-wave velocity structure from Altye Tagh to Longmen mountains along the Taiwan-Altay geoscience transect. Chinese J. Geophys. (in Chinese), 2005,48(1) :98-106
[14] Holbrook W H, Mooney W D, Christensen N I. The seismic velocity structure of the deep continental crust. In: Fountion D M eds. Continental Lower Crust, Developments in Geotectonics 23． 1992． 1-43
[15] Parker R L. The rapid calculation of potential anomalies. Geophys. J. R. astr. Soc. , 1973,31:447-455
[16] 朱迎堂,王绪本,余年等.龙门山大地电磁深部结构及汶川地震(M_s8． 0) .地质学报,2008,82(12) :1769-1777 Zhu Y T, Wang X B, Yu N, et al. Deep structure of magnetotelluric profile on Longmen Mts. and its relation to the M_s8． 0 Wenchuan earthquake. Acta Geologica Sinica (in Chinese), 2008, 82(12) :1769-1777
[1] 许志琴,李化启,侯立炜等.青藏高原东缘龙门-锦屏造山带的崛起--大型拆离断层和挤出机制.地质通报,2007,26(10) :1262-1267 Xu Z Q, Li H Q, Hou L W,et al. Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau:Large-scale detachment faulting and extrusion mechanism. Geological Bulletin of China ( in Chinese) , 2007,26(10) :1262-1276
[2] 四川省地质矿产局.四川省区域地质志.中华人民共和国地质矿产部地质专报,一区域地质,第23号.北京:地质出版社,1982 Bureau of Geology and Mineral Resources of Sichuan Province. Regional geology of Sichuan province, People s Republic of China, Ministry of Geology and Mineral Resources, Geological Memoirs, Series 1, Number 23 (in Chinese). Beijing: Geological Publishing House, 1982
[3] 宋鸿彪,刘树根.龙门山中北段重磁场特征与深部构造关系.成都地质学院学报,1991,18(1) :74-82 Song H B, Liu S G. The relation of gravity and aeromagnetic field and deep structure in middle-northern Longmenshan mountains. Journal of Chengdu College of Geology (in Chinese), 1991,18(1) :74-82
[4] 宋鸿彪.龙门山造山带地质和地球物理资料的综合解释.成都地质学院学报,1994,21(2) :79-87 Song H B. The comprehensive interpretation of geological and geophysical data in the orogenic belt of Longmen mountains. Journal of Chengdu College of Geology (in Chinese), 1994, 21(2) :79-87
[5] 王懋基.黑水-泉州地学断面的重磁解释.地球物理学报,1994,37(3) :321-329 Wang M J. Gravity and magnetic interpretation of Heishui-Quanzhou geoscience transect. Chinese J. Geophys. (in Chinese), 1994,37(3) :321-329
[6] 钟锴,徐鸣洁,王良书等.川滇地区重力场特征与地壳变形研究.高校地质学报,2005,11(1) :111-117 Zhong K, Xu M J, Wang L S, et al. Study on characteristics of gravity field and crustal deformation in Sichuan-Yunnan region. Geological Journal of China Universities (in Chinese), 2005,11(1) :111-117
[7] Frey H. MAGSAT scale anomaly distribution: the global perspective. Geophys. Res. Lett. ,1982,9(6) ,277-280
[8] Press W H, Teukolsky S A, Vetterling W T, et al. Numerical Recipes in Fortran 77． The Art of Scientific Computing, Second Edition, Cambridge University Press,1992
[9] Hornby P, Boschetti F, Horowitz F G. Analysis of potential field data in the wavelet domain. Geophys. J. Int. , 1999,137:175-196
[10] 崔作舟,陈纪平,吴苓.花石峡-邵阳深部地壳结构和构造.中华人民共和国地质矿产部地质专报,五构造地质、地质力学,第21号.北京:地质出版社,1996 Cui Z Z, Chen J P, Wu L. Texture and structure of Huashixia-Shaoyang deep crust, People s Republic of China, Ministry of Geology and Mineral Resources, Geological Memoirs, Series 5, Number 21 (in Chinese). Beijing: Geological Publishing House, 1996
[11] 朱介寿.汶川地震的岩石圈深部结构与动力学背景.成都理工大学学报(自然科学版),2008,35(4) :348-356 Zhu J S. The Wenchuan earthquake occurrence background in deep structure and dynamics of lithosphere. Journal of Chengdu University of Technology Cin Chinese), 2008, 35 (4) :348-356
[12] 贾东,陈竹新,贾承造等.龙门山前陆褶皱冲断带构造解析与川西前陆盆地的发育.高校地质学报,2003,9:402-410 Jia D, Chen Z X, Jia C Z, et al. Structural features of the Longmen Shan fold and thrust belt and development of the western Sichuan foreland basin, central China. Geological Journal of China Universities (in Chinese), 2003,9:402-410
[13] 王有学,Mooney W D,韩国花等.台湾-阿尔泰地学断面阿尔金龙门山剖面的地壳纵波速度结构.地球物理学报,2005,48(1) :98-106 Wang Y X, Mooney W D, Han G H, et al. Crustal P-wave velocity structure from Altye Tagh to Longmen mountains along the Taiwan-Altay geoscience transect. Chinese J. Geophys. (in Chinese), 2005,48(1) :98-106
[14] Holbrook W H, Mooney W D, Christensen N I. The seismic velocity structure of the deep continental crust. In: Fountion D M eds. Continental Lower Crust, Developments in Geotectonics 23． 1992． 1-43
[15] Parker R L. The rapid calculation of potential anomalies. Geophys. J. R. astr. Soc. , 1973,31:447-455
[16] 朱迎堂,王绪本,余年等.龙门山大地电磁深部结构及汶川地震(M_s8． 0) .地质学报,2008,82(12) :1769-1777 Zhu Y T, Wang X B, Yu N, et al. Deep structure of magnetotelluric profile on Longmen Mts. and its relation to the M_s8． 0 Wenchuan earthquake. Acta Geologica Sinica (in Chinese), 2008, 82(12) :1769-1777
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