龙门山断裂带及其周边地区重力场和岩石层力学特性研究
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摘要
继2008年汶川MS8.0地震之后,2013年4月20日又发生了芦山MS7.0地震,两次地震的发震构造同属龙门山断裂带.根据最新的重力和地形资料,采用岩石层弹性板模型,计算了龙门山断裂带及其周边地区的二维岩石层有效弹性厚度分布,并从岩石层的力学特征分析了穿过两次地震震中位置的重力剖面特征;结合以往在该地区的研究成果,分析了岩石层的力学变形问题.结果表明,以龙门山为界,四川盆地所在的扬子板块弹性厚度为33(±4)km,龙门山西北的松潘—甘孜地块的弹性厚度为13(±4)km,两侧岩石层存在明显的力学强度差异.包括两次地震震中范围的龙门山断裂带南部区域的有效弹性厚度值小于北部地区,说明该区域的岩石层更容易发生变形,可以解释在构造上具备强震发生的岩石层动力学条件.
After the 2008 Wenchuan MS8.0 earthquake,a MS7.0 earthquake occurred in Lushan County,Sichuan Province,on April 20,2013.The seismogenic structure of the two earthquakes both belong to Longmenshan fault zone.By using the latest gravity and topography dataset,this paper calculates 2D lithospheric effective elastic thickness of the Longmenshan fault zone and its surrounding areas with lithospheric elastic plate model.Based on the lithosphere mechanical properties,the characteristics of two gravity profiles which across the two epicenters are analyzed.And combining with previous researches in the area,the lithospheric mechanical deformation is also analyzed.The results show that,with the boundary of Longmenshan,the effective elastic thickness of Sichuan basin located on the Yangtze Plate is about 33(±4) km,whereas that of the Songpan--Garze block is about 13(±4) km at the northwest of Longmenshan,which indicates that the lithospheric mechanical strengths are obviously different for the two blocks.The effective elastic thickness of the southern Longmenshan region(including the scope of the two earthquake epicenters)is less than the northern,suggesting that the southern region is more prone to lithospheric deformation,which can be used to explain the lithospheric dynamic conditions for great earthquake occurrence in tectonics.
After the 2008 Wenchuan MS8.0 earthquake,a MS7.0 earthquake occurred in Lushan County,Sichuan Province,on April 20,2013.The seismogenic structure of the two earthquakes both belong to Longmenshan fault zone.By using the latest gravity and topography dataset,this paper calculates 2D lithospheric effective elastic thickness of the Longmenshan fault zone and its surrounding areas with lithospheric elastic plate model.Based on the lithosphere mechanical properties,the characteristics of two gravity profiles which across the two epicenters are analyzed.And combining with previous researches in the area,the lithospheric mechanical deformation is also analyzed.The results show that,with the boundary of Longmenshan,the effective elastic thickness of Sichuan basin located on the Yangtze Plate is about 33(±4) km,whereas that of the Songpan--Garze block is about 13(±4) km at the northwest of Longmenshan,which indicates that the lithospheric mechanical strengths are obviously different for the two blocks.The effective elastic thickness of the southern Longmenshan region(including the scope of the two earthquake epicenters)is less than the northern,suggesting that the southern region is more prone to lithospheric deformation,which can be used to explain the lithospheric dynamic conditions for great earthquake occurrence in tectonics.
引文
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Jin Y,McNutt M K,Zhu Y.1994.Evidence from gravity and topography data for folding of Tibet[J].Nature,371:669--674.doi:10.1038/371669a0.
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Sandwell D T,Smith W H F.1997.Marine gravity anomaly from Geosat and ERS 1satellite altimetry[J].J Geophys Res,102(B5):10039--10054.doi:10.1029/96JB03223.
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Smith W H F,Sandwell D T.1997.Global sea floor topography from satellite altimetry and ship depth soundings[J].Science,277(5334):1956--1962.doi:10.1126/science.277.5334.1956.
Turcotte D L,Suchubert G.2002.Geodynamics[M].2nd ed.Cambridge:Cambridge University Press:124--126.
Wang H,Liu M,Shen X,Liu J.2010.Balance of seismic moment in the Songpan—Ganze region,eastern Tibet:Implications for the 2008great Wenchuan earthquake[J].Tectonophysics,491(1):154--164.
Watts A B.2001.Isostasy and Flexure of the Lithosphere[M].New York:Cambridge University Press:186--189.
①http:∥topex.ucsd.edu/marine_grav/
陈运泰,杨智娴,张勇,刘超.2013.从汶川地震到芦山地震[J].中国科学:地球科学,43(6):1064--1072.
刘杰,易桂喜,张致伟,官致君,阮祥,龙锋,杜方.2013.2013年4月20日四川芦山M7.0级地震介绍[J].地球物理学报,56(4):1404--1407.
王卫民,郝金来,姚振兴.2013.2013年4月20日四川芦山地震震源破裂过程反演初步结果[J].地球物理学报,56(4):1412--1417.
张勇,许力生,陈运泰.2009.2008年汶川大地震震源机制的时空变化[J].地球物理学报,52(2):379--389.
郑勇,葛粲,谢祖军,Yang Y J,熊熊,许厚泽.2013.芦山与汶川地震震区地壳上地幔结构及深部孕震环境[J].中国科学:地球科学,43(6):1027--1037.
Braitenberg C,Wang Y,Fang J,Hsu H T.2003.Spatial variations of flexure parameters over the Tibet-Qinghai Plateau[J].Earth Planet Sci Lett,205(3/4):211--224.
Burchfiel B C,Royden L H,van der Hilst R D,Chen Z,King R W,Li C,Lu J,Yao H,Kirby E.2008.A geological and geophysical context for the Wenchuan earthquake of 12May 2008,Sichuan,People′s Republic of China[J].GSA Today,18(7):doi:10.1130/GSATG8A.1.
Chen B,Chen C,Kaban M K,Du J,Liang Q,Thomas M.2013.Variations of the effective elastic thickness over China and surroundings and their relation to the lithosphere dynamics[J].Earth Planet Sci Lett,363:61--72.
Fielding E J,McKenzie D.2012.Lithospheric flexure in the Sichuan basin and Longmenshan at the eastern edge of Tibet[J].Geophys Res Lett,39(09):L09311.doi:10.1029/2012GL051680.
Jiang X,Jin Y.2005.Mapping the deep lithospheric structure beneath the eastern margin of the Tibetan Plateau from gravity anomalies[J].J Geophys Res,110(B7)doi:10.1029/2004JB003394.
Jin Y,McNutt M K,Zhu Y.1994.Evidence from gravity and topography data for folding of Tibet[J].Nature,371:669--674.doi:10.1038/371669a0.
Jin Y,McNutt M K,Zhu Y S.1996.Mapping the descent of Indian and Eurasian plates beneath the Tibetan Plateau from gravity anomalies[J].J Geophys Res,101:11275--11290.
Jordan T A,Watts A B.2005.Gravity anomalies,flexure and the elastic thickness structure of the India-Eurasia collisional system[J].Earth Planet Sci Lett,236(3/4):732--750.
Sandwell D T,Smith W H F.1997.Marine gravity anomaly from Geosat and ERS 1satellite altimetry[J].J Geophys Res,102(B5):10039--10054.doi:10.1029/96JB03223.
Sandwell D T,Smith W H F.2009.Global marine gravity from retracked Geosat and ERS-1altimetry:Ridge segmentation versus spreading rate[J].J Geophys Res,114(B1)doi:10.1029/2008JB006008.
Smith W H F,Sandwell D T.1997.Global sea floor topography from satellite altimetry and ship depth soundings[J].Science,277(5334):1956--1962.doi:10.1126/science.277.5334.1956.
Turcotte D L,Suchubert G.2002.Geodynamics[M].2nd ed.Cambridge:Cambridge University Press:124--126.
Wang H,Liu M,Shen X,Liu J.2010.Balance of seismic moment in the Songpan—Ganze region,eastern Tibet:Implications for the 2008great Wenchuan earthquake[J].Tectonophysics,491(1):154--164.
Watts A B.2001.Isostasy and Flexure of the Lithosphere[M].New York:Cambridge University Press:186--189.
①http:∥topex.ucsd.edu/marine_grav/
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