用地震资料估计的龙门山断裂深部形变及其对于汶川地震成因的意义
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摘要
2008年5月12日汶川8.0级地震前龙门山断裂被"忽视"的原因之一是地质学证据和GPS测量证据均显示龙门山断裂长期以来形变速率很低。问题是,构造地质的结果是对一个较长的时间尺度的,而GPS结果反映的是较短时间尺度上的、地表上的、水平方向的形变,因此有理由怀疑由此得到的结论能否反映现今龙门山断裂的深部形变的全貌。我们采用类似于Kostrov方法的思路,利用最近30a的地震资料,试图研究龙门山断裂的深部形变,并与其相邻的断裂进行比较。利用ML2.5以上的微震资料,给出了沿龙门山断裂带的累积Benioff应变,并根据震级-频度关系计算了a值的空间分布。作为对照,同时计算了龙门山断裂邻区沿鲜水河、安宁河、则木河断裂各区域内的累积Benioff应变和a值。结果表明,在与地质学证据不同的时间尺度上,在与GPS证据不同的时间尺度、不同的深度上,并且不仅考虑到水平形变,与周边的断裂带相比,龙门山断裂带其实并不是一个"安静的"断裂带。在更短的时间尺度上,可以回溯性地观察到微震活动的一些异常变化,但这些变化似乎很难用于该地震的预测。我们讨论了相关的观测资料分析对于汶川地震的成因的意义。
One of the causes for the Longmenshan fault to be "neglected" before the May 12, 2008, Wenchuan, MS 8.0 earthquake was that geological evidences and GPS measurements all indicated that this fault is the one with extremely slow deformation rate. Suspecting that whether this conclusion holds for the real situation at depth because geological estimation deals with a very long time scale, and GPS measurement deals with the horizontal deformation at the surface of the Earth only within the recent decade, we tried to take the approach similar to Kostrov method to investigate the deep deformation using data of microseismicity since the recent 3 decades. We used local earthquake catalogues complete down to ML 2.5 to calculate the Benioff strain along the Longmenshan fault and the distribution of a-value in the Gutenberg-Richter frequency-magnitude relation. We considered the nearby Xianshuihe, Anninghe, and Zemuhe fault as a comparison. What is observed is that at the time scale different from geological process and GPS-observed deformation, for the depths different from the surface of ground, considering both horizontal and vertical deformation, and comparing with its neighboring fault systems, Longmenshan fault is indeed not as 'quiet' as traditionally assessed. At shorter time scale, some anomalous pattern of seismicity can be observed retrospectively before the Wenchuan earthquake, but they are hard to use as an indication of the approaching of this catastrophic event. Implication of the observations to the study of the Wenchuan earthquake is discussed.
One of the causes for the Longmenshan fault to be "neglected" before the May 12, 2008, Wenchuan, MS 8.0 earthquake was that geological evidences and GPS measurements all indicated that this fault is the one with extremely slow deformation rate. Suspecting that whether this conclusion holds for the real situation at depth because geological estimation deals with a very long time scale, and GPS measurement deals with the horizontal deformation at the surface of the Earth only within the recent decade, we tried to take the approach similar to Kostrov method to investigate the deep deformation using data of microseismicity since the recent 3 decades. We used local earthquake catalogues complete down to ML 2.5 to calculate the Benioff strain along the Longmenshan fault and the distribution of a-value in the Gutenberg-Richter frequency-magnitude relation. We considered the nearby Xianshuihe, Anninghe, and Zemuhe fault as a comparison. What is observed is that at the time scale different from geological process and GPS-observed deformation, for the depths different from the surface of ground, considering both horizontal and vertical deformation, and comparing with its neighboring fault systems, Longmenshan fault is indeed not as 'quiet' as traditionally assessed. At shorter time scale, some anomalous pattern of seismicity can be observed retrospectively before the Wenchuan earthquake, but they are hard to use as an indication of the approaching of this catastrophic event. Implication of the observations to the study of the Wenchuan earthquake is discussed.
引文
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江在森,马宗晋,张希,王琪,王双绪.2003.GPS初步结果揭示的中国大陆水平应变场与构造变形.地球物理学报,46(3):352~358.
李延兴,杨国华,李智,郭良迁,黄-,朱文耀,符养,王琪,江在森,王敏.2003.中国大陆活动地块的运动与应变状态.中国科学(D辑),33(增刊):65~81.
沈正康,王敏,甘卫军,张祖胜.2003.中国大陆现今构造应变率场及其动力学成因研究.地学前缘,10(增刊):93~100.
苏有锦,李永莉,李忠华,易桂喜,刘丽芳.2003.川滇地区区域地震目录完整性最小震级分析.地震研究,26(增刊):10~16.
王敏,沈正康,牛之俊,张祖胜,孙汉荣,甘卫军,王琪,任群.2003.现今中国大陆地壳运动与活动块体模型.中国科学(D辑),33(增刊):21~32.
徐锡伟,闻学泽,郑荣章,马文涛,宋方敏,于贵华.2003.川滇地区活动块体最新构造变动样式及其动力来源.中国科学(D辑),33(增刊):151~162.
徐锡伟,张培震,闻学泽,秦尊丽,陈桂华,朱艾斓.2005.川西及其邻近地区活动构造基本特征与强震复发模型.地震地质,27(3):446~461.
许忠淮.2001.东亚地区现今构造应力图的编制.地震学报,23(5):492~501.
易桂喜,闻学泽,徐锡伟.2002.川滇地区若干活动断裂带整体的强地震复发特征研究.中国地震,18(3):267~276.
易桂喜,闻学泽,范军,王思维.2004.由地震活动参数分析安宁-则木河断裂带的现今活动性及地震危险性.地震学报,2(3):294~303.
易桂喜,范军,闻学泽.2005.由现今地震活动分析鲜水河断裂带中-南段活动习性与强震危险地段.地震,25(1):58~66.
易桂喜,闻学泽,王思维,龙锋,范军.2006.由地震活动参数分析龙门山-岷山断裂带的现今活动习性与强震危险性.中国地震,22(2):117~125.
张国民,张晓东,刘杰,刘耀炜,田勤俭,郝平,马宏生,焦明若.2005.印尼苏门答腊8.7级大震对中国陆区的影响.地震,25(4):15~25.
张培震,王敏,甘卫军,邓起东.2003.GPS观测的活动断裂滑动速率及其对现今大陆动力作用的制约.地学前缘,10(增刊):81~92.
张培震,徐锡伟,闻学泽,冉勇康.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,51(4):1066~1073.
Aki K.1965.Maxi mumlikelihood esti mate ofbinthe formulalogN=a-bMand its confidence li mits.Bulletin of the EarthquakeResearch Institute,University of Tokyo,43(2):237~239.
Aki K.1981.A probabilistic synthesis of precursory phenomena.In:Si mpson D W,Richards P G,eds.Earthquake Prediction:An International Review.American Geophysical Union,Washington,D.C.,566~574.
Benioff H.1951.Earthquake and rock creep(Part I:Creepcharacteristics of rocks and the origin of aftershocks).Bulletinof the Seismological Society of America,41(1):31~62.
Ben-Zion Y,Sammis C G.2003.Characterization of fault zones.Pure and Applied Geophysics,160(3~4):677~715.
Bowman D,King G C P.2001.Accelerating seismicity and stressaccumulation before large earthquakes.Geophysical ResearchLetters,28(21):4039~4042.
Chen Z,Burchfiel B C,Liu Y,King R W,Royden L H,Tang W,Wang E,Zhao J,Zhang X.2000.Global Positioning Systemmeasurements from eastern Tibet and their i mplications forIndia/Eurasia intercontinental deformation.Journal ofGeophysical Research,105(B7):16215~16227.
Densmore A L,Ellis M A,Li Y,Zhou R J,Hancock G S,Richardson N.2007.Active tectonics of the Beichuan andPengguan faults at the eastern margin of the Tibetan Plateau.Tectonics,26(4):TC4005,doi:10.1029/2006TC001987.
Dong S W,Zhang Y Q,Wu Z H,Yang N,Ma YS,Shi W,Chen ZL,Long C X,An MJ.2008.Surface rupture and co-seismicdisplacement produced by theMS8.0Wenchuan earthquake ofMay12th,2008,Sichuan,China:Eastwards growth of theQinghai-Tibet Plateau.Acta Geologica Sinica,82(5):938~948.
Gardner J K,Knopoff L.1974.Is the sequence of earthquakes inSouthern California,with aftershocks removed,Poissonian-Bulletin of the Seismological Society of America,64(5):1363~1367.
Holt WE,Chamot-Rooke N,Le Pichon X,Haines A J,Shen-Tu B,Ren J.2000.Velocityfieldin Asiainferredfrom Quaternaryfault slip rates and Global Positioning System observations.Journal of Geophysical Research,105(B8):19185~19209.
Jaum S C,Sykes L R.1999.Evolving towards a critical point:Areview of accelerating seismic moment:Energy release prior tolarge and great earthquakes.Pure and Applied Geophysics,155(2~4):279~306.
Jiang C S,Wu Z L.2005.Test of the preshock accelerating momentrelease(AMR)in the case of the26December2004MW9.0Indonesia earthquake.Bulletin of the Seismological Society ofAmerica,95(5):2016~2025.
Kanamori H.1977.The energy release in great earthquakes.Journal of Geophysics Research,82(B20):2981~2987.
King R W,Shen F,Burchfiel B C,Royden L H,Wang E,Chen ZL,Liu Y P,Zhang X Y,Zhao J X,Li Y L.1997.Geodeticmeasurement of crustal motion in southwest China.Geology,25(2):179~182.
Kostrov B V.1974.Seismic moment and energy of earthquakes,andseismic flow of rock.Izvestiya,Academy of Sciences,USSR,Physics of the Solid Earth,1:23~40.
Main I G.1995.Earthquakes as critical phenomena:I mplicationsfor probabilistic seismic hazard analysis.Bulletin of theSeismological Society of America,85(5):1299~1308.
Mignan A,King G C P,Bowman D.2007.A mathematicalformulation of accelerating moment release based on the stressaccumulation model.Journal of Geophysical Research,112(B7):B07308,doi:10.1029/2006JB004671.
Parsons T,Ji C,Kirby E.2008.Stress changes from the2008Wenchuan earthquake and increased hazard in the Sichuanbasin.Nature,454(7203):509~510.
Robinson R.2000.A test of the precursory accelerating momentrelease model on some recent New Zealand earthquakes.Geophysical Journal International,140(3):568~576.
Scholz C H.1968.The frequency-magnitude relation ofmicrofracturingin rock andits relation to earthquakes.Bulletinof the Seismological Society of America,58(1):399~415.
Singh C,Bhattacharya P M,Chadha R K.2008.Seismicity in theKoyna-Warna reservoir site in Western India:Fractal andb-value mapping.Bulletin of the Seismological Society ofAmerica,98(1):476~482.
Utsu T.1965.A methodfor determining the value ofbin a formulalogn=a-b Mshowing the magnitude-frequency relation forearthquakes.Geophysical Bulletin of Hokkaido University,13:99~103(in Japanese with English abstract).
Vere-Jones D,Robinson R,Yang W Z.2001.Remarks on theaccelerated moment release model:Problems of modelformulation,si mulation and esti mation.Geophysical JournalInternational,144(3):517~531.
Wang L F,Ma S L,Ma L.2008.Accelerating moment release ofacoustic emission during rock deformation in the laboratory.Pure and Applied Geophysics,165(2):181~199.
Wang Q,Zhang P Z,Freymueller J T,Bilham R,Larson K M,LaiX A,You X Z,Niu ZJ,Wu J C,Li Y X,Liu J N,Yang Z Q,Chen Q Z.2001.Present-day crustal deformation in Chinaconstrained by Global Positioning System measurements.Science,294(5542):574~577.
Ward S N.1998a.On the consistency of earthquake moment rates,geological fault data,and space geodetic strain:the United States.Geophysical Journal International,134(1):172~186.
Ward S N.1998b.Onthe consistency of earthquake moment releaseand space geodetic strain rates:Europe.Geophysical JournalInternational,135(3):1011~1018.
Wyss M,Brune J N.1967.The Alaska earthquake of28March1964:Acomplex multiple rupture.Bulletin of the SeismologicalSociety of America,57(5):1017~1023.
Wyss M,Sammis C G,Nadeau R M,Wiemer S.2004.Fractaldi mension andb-value on creeping andlocked patches of the SanAndreas Fault near Parkfield,California.Bulletin of theSeismological Society of America,94(2):410~421.
Xu Z Q,Ji S C,Li HB,Hou L W,Fu X F,Cai Z H.2008.Upliftof the Longmen Shan range and the Wenchuan earthquake.Episodes,31(3):291~301.
Zhang P Z,Shen Z K,Wang M,Gan WJ,Brgmann R,Molnar P,Wang Q,Niu ZJ,Sun J Z,Wu J C,Sun HR,You XZ.2004.Continuous deformation of the Tibetan Plateau from globalpositioning systemdata.Geology,32(9):809~812.
Zhou RJ,Li Y,Densmore A L,Ellis M A,He Y L,Li Y Z,Li XG.2007.Active tectonics of the Longmen Shan region on theeastern margin of the Tibetan plateau.Acta Geologica Sinica,81(4):593~604.
付虹,刘强,邬成栋,王永安,吴小平.2007.印尼8.7、8.5级远震对云南地区小震的激发和地下流体异常响应初探.地震研究,30(1):8~13.
江在森,马宗晋,张希,王琪,王双绪.2003.GPS初步结果揭示的中国大陆水平应变场与构造变形.地球物理学报,46(3):352~358.
李延兴,杨国华,李智,郭良迁,黄-,朱文耀,符养,王琪,江在森,王敏.2003.中国大陆活动地块的运动与应变状态.中国科学(D辑),33(增刊):65~81.
沈正康,王敏,甘卫军,张祖胜.2003.中国大陆现今构造应变率场及其动力学成因研究.地学前缘,10(增刊):93~100.
苏有锦,李永莉,李忠华,易桂喜,刘丽芳.2003.川滇地区区域地震目录完整性最小震级分析.地震研究,26(增刊):10~16.
王敏,沈正康,牛之俊,张祖胜,孙汉荣,甘卫军,王琪,任群.2003.现今中国大陆地壳运动与活动块体模型.中国科学(D辑),33(增刊):21~32.
徐锡伟,闻学泽,郑荣章,马文涛,宋方敏,于贵华.2003.川滇地区活动块体最新构造变动样式及其动力来源.中国科学(D辑),33(增刊):151~162.
徐锡伟,张培震,闻学泽,秦尊丽,陈桂华,朱艾斓.2005.川西及其邻近地区活动构造基本特征与强震复发模型.地震地质,27(3):446~461.
许忠淮.2001.东亚地区现今构造应力图的编制.地震学报,23(5):492~501.
易桂喜,闻学泽,徐锡伟.2002.川滇地区若干活动断裂带整体的强地震复发特征研究.中国地震,18(3):267~276.
易桂喜,闻学泽,范军,王思维.2004.由地震活动参数分析安宁-则木河断裂带的现今活动性及地震危险性.地震学报,2(3):294~303.
易桂喜,范军,闻学泽.2005.由现今地震活动分析鲜水河断裂带中-南段活动习性与强震危险地段.地震,25(1):58~66.
易桂喜,闻学泽,王思维,龙锋,范军.2006.由地震活动参数分析龙门山-岷山断裂带的现今活动习性与强震危险性.中国地震,22(2):117~125.
张国民,张晓东,刘杰,刘耀炜,田勤俭,郝平,马宏生,焦明若.2005.印尼苏门答腊8.7级大震对中国陆区的影响.地震,25(4):15~25.
张培震,王敏,甘卫军,邓起东.2003.GPS观测的活动断裂滑动速率及其对现今大陆动力作用的制约.地学前缘,10(增刊):81~92.
张培震,徐锡伟,闻学泽,冉勇康.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,51(4):1066~1073.
Aki K.1965.Maxi mumlikelihood esti mate ofbinthe formulalogN=a-bMand its confidence li mits.Bulletin of the EarthquakeResearch Institute,University of Tokyo,43(2):237~239.
Aki K.1981.A probabilistic synthesis of precursory phenomena.In:Si mpson D W,Richards P G,eds.Earthquake Prediction:An International Review.American Geophysical Union,Washington,D.C.,566~574.
Benioff H.1951.Earthquake and rock creep(Part I:Creepcharacteristics of rocks and the origin of aftershocks).Bulletinof the Seismological Society of America,41(1):31~62.
Ben-Zion Y,Sammis C G.2003.Characterization of fault zones.Pure and Applied Geophysics,160(3~4):677~715.
Bowman D,King G C P.2001.Accelerating seismicity and stressaccumulation before large earthquakes.Geophysical ResearchLetters,28(21):4039~4042.
Chen Z,Burchfiel B C,Liu Y,King R W,Royden L H,Tang W,Wang E,Zhao J,Zhang X.2000.Global Positioning Systemmeasurements from eastern Tibet and their i mplications forIndia/Eurasia intercontinental deformation.Journal ofGeophysical Research,105(B7):16215~16227.
Densmore A L,Ellis M A,Li Y,Zhou R J,Hancock G S,Richardson N.2007.Active tectonics of the Beichuan andPengguan faults at the eastern margin of the Tibetan Plateau.Tectonics,26(4):TC4005,doi:10.1029/2006TC001987.
Dong S W,Zhang Y Q,Wu Z H,Yang N,Ma YS,Shi W,Chen ZL,Long C X,An MJ.2008.Surface rupture and co-seismicdisplacement produced by theMS8.0Wenchuan earthquake ofMay12th,2008,Sichuan,China:Eastwards growth of theQinghai-Tibet Plateau.Acta Geologica Sinica,82(5):938~948.
Gardner J K,Knopoff L.1974.Is the sequence of earthquakes inSouthern California,with aftershocks removed,Poissonian-Bulletin of the Seismological Society of America,64(5):1363~1367.
Holt WE,Chamot-Rooke N,Le Pichon X,Haines A J,Shen-Tu B,Ren J.2000.Velocityfieldin Asiainferredfrom Quaternaryfault slip rates and Global Positioning System observations.Journal of Geophysical Research,105(B8):19185~19209.
Jaum S C,Sykes L R.1999.Evolving towards a critical point:Areview of accelerating seismic moment:Energy release prior tolarge and great earthquakes.Pure and Applied Geophysics,155(2~4):279~306.
Jiang C S,Wu Z L.2005.Test of the preshock accelerating momentrelease(AMR)in the case of the26December2004MW9.0Indonesia earthquake.Bulletin of the Seismological Society ofAmerica,95(5):2016~2025.
Kanamori H.1977.The energy release in great earthquakes.Journal of Geophysics Research,82(B20):2981~2987.
King R W,Shen F,Burchfiel B C,Royden L H,Wang E,Chen ZL,Liu Y P,Zhang X Y,Zhao J X,Li Y L.1997.Geodeticmeasurement of crustal motion in southwest China.Geology,25(2):179~182.
Kostrov B V.1974.Seismic moment and energy of earthquakes,andseismic flow of rock.Izvestiya,Academy of Sciences,USSR,Physics of the Solid Earth,1:23~40.
Main I G.1995.Earthquakes as critical phenomena:I mplicationsfor probabilistic seismic hazard analysis.Bulletin of theSeismological Society of America,85(5):1299~1308.
Mignan A,King G C P,Bowman D.2007.A mathematicalformulation of accelerating moment release based on the stressaccumulation model.Journal of Geophysical Research,112(B7):B07308,doi:10.1029/2006JB004671.
Parsons T,Ji C,Kirby E.2008.Stress changes from the2008Wenchuan earthquake and increased hazard in the Sichuanbasin.Nature,454(7203):509~510.
Robinson R.2000.A test of the precursory accelerating momentrelease model on some recent New Zealand earthquakes.Geophysical Journal International,140(3):568~576.
Scholz C H.1968.The frequency-magnitude relation ofmicrofracturingin rock andits relation to earthquakes.Bulletinof the Seismological Society of America,58(1):399~415.
Singh C,Bhattacharya P M,Chadha R K.2008.Seismicity in theKoyna-Warna reservoir site in Western India:Fractal andb-value mapping.Bulletin of the Seismological Society ofAmerica,98(1):476~482.
Utsu T.1965.A methodfor determining the value ofbin a formulalogn=a-b Mshowing the magnitude-frequency relation forearthquakes.Geophysical Bulletin of Hokkaido University,13:99~103(in Japanese with English abstract).
Vere-Jones D,Robinson R,Yang W Z.2001.Remarks on theaccelerated moment release model:Problems of modelformulation,si mulation and esti mation.Geophysical JournalInternational,144(3):517~531.
Wang L F,Ma S L,Ma L.2008.Accelerating moment release ofacoustic emission during rock deformation in the laboratory.Pure and Applied Geophysics,165(2):181~199.
Wang Q,Zhang P Z,Freymueller J T,Bilham R,Larson K M,LaiX A,You X Z,Niu ZJ,Wu J C,Li Y X,Liu J N,Yang Z Q,Chen Q Z.2001.Present-day crustal deformation in Chinaconstrained by Global Positioning System measurements.Science,294(5542):574~577.
Ward S N.1998a.On the consistency of earthquake moment rates,geological fault data,and space geodetic strain:the United States.Geophysical Journal International,134(1):172~186.
Ward S N.1998b.Onthe consistency of earthquake moment releaseand space geodetic strain rates:Europe.Geophysical JournalInternational,135(3):1011~1018.
Wyss M,Brune J N.1967.The Alaska earthquake of28March1964:Acomplex multiple rupture.Bulletin of the SeismologicalSociety of America,57(5):1017~1023.
Wyss M,Sammis C G,Nadeau R M,Wiemer S.2004.Fractaldi mension andb-value on creeping andlocked patches of the SanAndreas Fault near Parkfield,California.Bulletin of theSeismological Society of America,94(2):410~421.
Xu Z Q,Ji S C,Li HB,Hou L W,Fu X F,Cai Z H.2008.Upliftof the Longmen Shan range and the Wenchuan earthquake.Episodes,31(3):291~301.
Zhang P Z,Shen Z K,Wang M,Gan WJ,Brgmann R,Molnar P,Wang Q,Niu ZJ,Sun J Z,Wu J C,Sun HR,You XZ.2004.Continuous deformation of the Tibetan Plateau from globalpositioning systemdata.Geology,32(9):809~812.
Zhou RJ,Li Y,Densmore A L,Ellis M A,He Y L,Li Y Z,Li XG.2007.Active tectonics of the Longmen Shan region on theeastern margin of the Tibetan plateau.Acta Geologica Sinica,81(4):593~604.
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