拉萨和羌塘地块地震活动和热前兆现象及其机理研究
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摘要
青藏地块活动区南部的II级拉萨和羌塘地块内部的M≥6.5强震活动比北部的巴颜喀拉、柴达木和祁连II级地块内部明显活跃,这可能与拉萨和羌塘地块处于地壳厚度较大、较高的热状态和较低的正断层剪切强度等地学背景下,导致地壳强度较弱有关。拉萨和羌塘地块内部两次拉张性正断层活动的强震(2008年于田7.3级和当雄6.6级)前热异常的震例,可能与临震前孕震区及邻近断层带扩容,以及中下地壳低速层熔融物质或流体的进入有关。
There are relatively active strong seismicity inside the second-order Lasa and Qiangtang blocks compared with other blocks in the first-order Qing-Zang active block region,which might be related to the weaker crust strength due to thicker crust,higher heat and lower shear strength on normal fault there.Inside the second-order Lasa and Qiangtang active blocks,cases of abnormal heat phenomenon have been observed before two strong earthquakes(M7.3 Yutian earthquake and M6.6 Danxion earthquake in 2008),which might be related to the dilatation in the faults of earthquake preparation region and nearby,where melting material and liquid enter into from the low velocity layer in upper-middle crust.
There are relatively active strong seismicity inside the second-order Lasa and Qiangtang blocks compared with other blocks in the first-order Qing-Zang active block region,which might be related to the weaker crust strength due to thicker crust,higher heat and lower shear strength on normal fault there.Inside the second-order Lasa and Qiangtang active blocks,cases of abnormal heat phenomenon have been observed before two strong earthquakes(M7.3 Yutian earthquake and M6.6 Danxion earthquake in 2008),which might be related to the dilatation in the faults of earthquake preparation region and nearby,where melting material and liquid enter into from the low velocity layer in upper-middle crust.
引文
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[16]许忠淮.东亚地区现今构造应力图的编制[J].地震学报,2001,23(5):492-501.
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[22]Brace WF,Paulding B W,Scholz C H.Dilatancyin the fracture of crystalline rocks[J].J GeophysRes,1966,71:3939-3953.
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①http://neic.usgs.gov/neis/bulletin/
②http://neic.usgs.gov/neis/bulletin/
①邓志辉,卫星红外观测与地震前亮温异常特征研究,2009年。
[2]Tsapanos T M,Papazachos B C.Geographical and vertical variation of the earth′s seismicity[J].JSeismology,1998,2:183-192.
[3]Armijo R,Tapponnier P,Mercier J L,et al.Quaternary extensionin southern Tibet:field observa-tion and tectonic i mplication[J].J Geophys Res,1986,91(B14):13803-13872.
[4]中国地震局地质研究所.西藏中部活动断层[M].北京:地震出版社,1992.
[5]Yin A,Kapp P A,Murphy MA,et al.Significant late Neogene east-west extensionin northern Ti-bet[J].Geology,1999,25:787-790.
[6]Braitenberg C,Zadro M,Fang J,et al.Gravity inversionin Qinghai-Tibet plateau[J].Phys ChemEarth(A),2000,25(4):381-386.
[7]Kind R,Ni J,Zhao W,et al.Evidence from Earthquake Data for a Partially Molten Crustal Layer inSouthern Tibet[J].Science,1996,274(5293):1692-1694.
[8]李永华,曾融生,吴庆举,等.青藏高原拉萨及羌塘块体的地壳结构研究[J].地震学报,2006,28(6):586-595.
[9]江在森,杨国华,等.大地形变在2006—2020年中国大陆强震危险区预测中的应用研究[A].“2006—2020年中国大陆强震危险区与地震灾害预测研究”项目组.2006—2020年中国大陆强震危险区与地震灾害预测研究[C].北京:地震出版社,2007.98-101.
[10]王洪涛,范光禄.热震状态[A].马杏垣.中国岩石圈动力学图集[C].北京:地震出版社,1989.15.
[11]汪素云,高阿甲,许忠淮,等.青藏高原东北地区地震重新定位及其活动特征[J].地震学报,2000,22(3):241-248.
[12]Liang Xiaofeng,Shiyong Zhou,John Chen Y,et al.Earthquake distribution in southern Tibet andits tectonic i mplications[J].J Geopgys Res,2008,113,B12409,doi:10.1029/2007 JB005101.
[13]Molnar P,Tapponnier P.Active tectonics of Tibet[J].J Geophys Res,1978,85:5361-5384.
[14]Ni J,Barazangi M.Seismotectonics of Hi malayan collision zone:Geometry of underthrusting Indiaplate beneath the Hi malaya[J].J Geophys Res,1984,89:1147-1163.
[15]郑斯华,高原.青藏高原的地震学研究(综述)[A].马宗晋,汪一鹏,张燕平主编.青藏高原岩石圈现今变动与动力学[C].北京:地震出版社,2001.223-239.
[15]Molnar P,Lyon-Caen H.Fault plane solutions of earthquakes and active tectonics of the Tibet anPlateau and its margin[J].Geophys J Int,1989,99:123-153.
[16]许忠淮.东亚地区现今构造应力图的编制[J].地震学报,2001,23(5):492-501.
[17]熊熊.青藏高原岩石圈强度的弱化[A].马宗晋,汪一鹏,张燕平主编.青藏高原岩石圈现今变动与动力学[C].北京:地震出版社,2001.172-176.
[18]Sibson R H.Frictional constraints on thrust,wrench and normal faults[J].Nature,1974,249:542-545.
[19]Brace W F,Kohlstedt D.Li mits on lithospheric stress i mposed by laboratory experi ments[J].JGeophys Res,1980,85:6248-6252.
[20]Kirby S.Tectonic stress in the lithosphere:Constraints provided by the experi mental deformation ofrock[J].J Geophys Res,1980,85:6353-6363.
[21]Scholz C H.地震与断层力学[M].马胜利等译校.北京:地震出版社,1996.134.
[22]Brace WF,Paulding B W,Scholz C H.Dilatancyin the fracture of crystalline rocks[J].J GeophysRes,1966,71:3939-3953.
[23]Gaillard F,Scaillet B,Pichavant M.Evidence for present-day leucogranite pluton growth in Tibet[J].Geology,2004,32(9):801-804.
[24]Scholz C H,Sykes L R,Aggarwal Y P.Earthquake prediction:Aphysical basis[J].Science,1973,181:803-809.
①http://neic.usgs.gov/neis/bulletin/
②http://neic.usgs.gov/neis/bulletin/
①邓志辉,卫星红外观测与地震前亮温异常特征研究,2009年。
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