玉树地区地壳介质的各向异性特征
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摘要
本文利用2010年5月7日到10月18日玉树地震震源区及其周边22个地震台站记录的2010年4月14日玉树地震余震数据资料,使用剪切波分裂分析方法初步得到了每一个台站的剪切波快波偏振方向和慢波时间延迟,并分析了玉树及周边地区地壳介质各向异性特征.在该研究区域,甘孜—玉树断裂上部分台站快波偏振方向近于东西向,这一结果与该区域的水平主压应力方向一致.甘孜—玉树断裂带南段玉树周边的台站快剪切波偏振方向为南东向,与断裂带的走向一致,显示了此次地震断裂走滑性质的特征.位于杂多断裂和清水河断裂上的台站及其附近的台站,快波偏振方向与所处的断裂走向基本一致,多为南东东向.各个台站的慢波延迟时间结果分布在4.23～7.01ms/km范围内,平均慢波延迟时间是5.68ms/km.在甘孜—玉树断裂带和乌兰乌拉湖—玉树南断裂相交的位置慢波延时总体较高;而低值区位于打贝通—小苏莽断裂的北西端与杂多断裂之间的位置.沿玉树断裂带,慢波延迟时间的梯度值较大,本文这一结果揭示了慢波延迟时间的分布和破裂带的走向、余震的分布有很大关系.
This work uses seismic data of the aftershock sequence of the 14 April 2010 Yushu earthquake recorded by 22 seismic stations at the Yushu epicenter and surrounding areas from 7 May 2010 to 18 October 2010 and the analysis method of shear-waves splitting to determine the polarization direction of fast shear-wave and the delay time of slow shear-wave below every station,and analyze the crustal anisotropic characteristics in Yushu and adjacent areas.The results show that the polarization directions of fast shear-waves at some stations which are located at the Garzê-Yushu fault zone are nearly in the east-west direction,consistent with the direction of the horizontal principal compressive stress in this region.The polarization directions of fast shear-waves at stations which are around the Yushu station located at south of the Garzê-Yushu fault belt are southeast,which is consistent with the strike of the faults.These patterns of the polarization directions of fast shear-waves indicate that this fault on which the earthquake happened is a strike-slip fault.The polarization directions of fast shear-waves of stations located at and around the Zadoi fault and Qingshuihe fault are the same as the strike of the faults,which are SEE direction.The delay time of slow shear-wave of every station is in the range of 4.23～7.01 ms/km,and the average delay time of the slow wave is 5.68 ms/km in the study area.The slow-wave delay time is higher in the intersection location between the Garzê-Yushu fault belt and Ulan Ul lake-Yushu South fault.And the area with lower values is located at the position which is between the northwestern segment of the Dabeitong-Xiao Surmang fault and Zadoi fault belt.The gradient of the slow-wave delay time is higher along the Yushu fault zone.This paper indicates that there is a definite relationship between the distribution of the slow-wave delay time,the strike of rupture zone and the distribution of aftershocks.
This work uses seismic data of the aftershock sequence of the 14 April 2010 Yushu earthquake recorded by 22 seismic stations at the Yushu epicenter and surrounding areas from 7 May 2010 to 18 October 2010 and the analysis method of shear-waves splitting to determine the polarization direction of fast shear-wave and the delay time of slow shear-wave below every station,and analyze the crustal anisotropic characteristics in Yushu and adjacent areas.The results show that the polarization directions of fast shear-waves at some stations which are located at the Garzê-Yushu fault zone are nearly in the east-west direction,consistent with the direction of the horizontal principal compressive stress in this region.The polarization directions of fast shear-waves at stations which are around the Yushu station located at south of the Garzê-Yushu fault belt are southeast,which is consistent with the strike of the faults.These patterns of the polarization directions of fast shear-waves indicate that this fault on which the earthquake happened is a strike-slip fault.The polarization directions of fast shear-waves of stations located at and around the Zadoi fault and Qingshuihe fault are the same as the strike of the faults,which are SEE direction.The delay time of slow shear-wave of every station is in the range of 4.23～7.01 ms/km,and the average delay time of the slow wave is 5.68 ms/km in the study area.The slow-wave delay time is higher in the intersection location between the Garzê-Yushu fault belt and Ulan Ul lake-Yushu South fault.And the area with lower values is located at the position which is between the northwestern segment of the Dabeitong-Xiao Surmang fault and Zadoi fault belt.The gradient of the slow-wave delay time is higher along the Yushu fault zone.This paper indicates that there is a definite relationship between the distribution of the slow-wave delay time,the strike of rupture zone and the distribution of aftershocks.
引文
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[17]闻学泽,黄圣睦,江在雄.甘孜—玉树断裂带的新构造特征与地震危险性估计.地震地质,1985,7(3):23-34.Wen X Z,Huang S M,Jiang Z X.Neotectonic features ofthe Garzê-Yushu fault zone and assessment of its earthquakerisk.Seismology and Geology(in Chinese),1985,7(3):23-34.
[18]彭华,马秀敏,白嘉启等.甘孜—玉树断裂带第四纪活动特征.地质力学学报,2006,12(3):295-304.Peng H,Ma X M,Bai J Q,et al.Characteristics ofQuaternary activities of the Garzê-Yushu fault zone.Journalof Geomechanics(in Chinese),2006,12(3):295-304.
[19]Crampin S,Peacock S.A review of shear-wave splitting inthe compliant crack-critical anisotropic earth.Wave Motion,2005,41(1):59-77.
[20]Menke W,Brandsdottir B,Jakobsdottir S,et al.Seismicanisotropy in the crust at the mid-Atlantic plate boundary insouth-west Iceland.Geophys.J.Int.,1994,119(3):783-790.
[21]Bowman J R,Ando M.Shear-wave splitting in the upper-mantle wedge above the Tonga subduction zone.Geophys.J.Int.,1987,88(1):25-41.
[22]Gao Y,Crampin S.Temporal variations of shear-wavesplitting in field and laboratory studies in China.J.Appl.Geophys.,2003,54(3):279-287.
[23]石玉涛,高原,赵翠萍等.汶川地震余震序列的地震各向异性.地球物理学报,2009,52(2):398-407.Shi Y T,Gao Y,Zhao C P,et al.A study of seismicanisotropy of Wenchuan earthquake sequence.Chinese J.Geophys.(in Chinese),2009,52(2):398-407.
[24]高原,郑斯华,王培德.海南省东方地区1992年小震群剪切波分裂研究.地球物理学报,1996,39(2):221-232.Gao Y,Zheng S H,Wang P D.Shear wave splitting study onsmall earthquake swarm of 1992in Dongfang of Hainan,South China.Chinese J.Geophys.(in Chinese),1996,39(2):221-232.
[25]高原,梁维,丁香等.云南2001年施甸地震的剪切波分裂参数变化特征.地震学报,2004,26(6):576-582.Gao Y,Liang W,Ding X,et al.Variational characteristicsof shear-wave splitting on the 2001Shidian earthquakes inYunnan,China.Acta Seismologica Sinica(in Chinese),2004,26(6):576-582.
[26]Niu F L,Li J.Component azimuths of the CEArray stationsestimated from P-wave particle motion.Earthquake Science,2011,24(1):3-13.
[27]Silver P G,Chan W W.Shear wave splitting andsubcontinental mantle deformation.J.Geophys.Res.,1991,96(B10):16429-16545.
[28]Hudson J A.Wave speeds and attenuation of elastic waves inmaterial containing cracks.Geophys.J.R.Astr.Soc.,1981,64(1):133-150.
[29]庄真,傅竹武,吕梓龄等.青藏高原及邻近地区地壳与上地幔剪切波三维速度结构.地球物理学报,1992,35(6):694-709.Zhuang Z,Fu Z W,LüZ L,et al.3-D shear velocity modelof crust and upper mantle beneath the Tibetan Plateau and itsadjacent regions.Chinese J.Geophys.(in Chinese),1992,35(6):694-709.
[30]Crampin S.The fracture criticality of crustal rocks.Geophys.J.Int.,1994,118(2):428-438.
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[32]王琪,张培震,牛之俊等.中国大陆现今地壳运动和构造变形.中国科学(D),2001,31(7):529-536.Wang Q,Zhang P Z,Niu Z J,et al.Crustal movement andtectonic deformation of continental China.Science in China(D)(in Chinese),2001,31(7):529-536.
[33]叶正仁,王健.中国大陆现今地壳运动的动力学机制.地球物理学报,2004,47(3):456-461.Ye Z R,Wang J.Dynamics of present-day crustal movementin the China mainland.Chinese J.Geophys.(in Chinese),2004,47(3):456-461.
[34]许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5):492-501.Xu Z H.A present-day tectonic stress map for Eastern Asiaregion.Acta Seismologica Sinica(in Chinese),2001,23(5):492-501.
[35]赖院根,刘启元,陈九辉等.首都圈地区横波分裂与地壳应力场特征.地球物理学报,2006,49(1):189-196.Lai Y G,Liu Q Y,Chen J H,et al.Shear wave splitting andthe features of the crustal stress field in the Capital circle.Chinese J.Geophys.(in Chinese),2006,49(1):189-196.
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[2]陈立春,王虎,冉勇康等.玉树Ms7.1级地震地表破裂与历史大地震.科学通报,2010,55(13):1200-1205.Chen L C,Wang H,Ran Y K,et al.The Ms7.1 Yushuearthquake surface rupture and large historical earthquakeson the Garzê-Yushu fault.Chinese Sci.Bull.,2010,55(31):3504-3509.
[3]Crampin S,Booth D C.Shear-wave polarizations near theNorth Anatolian Fault,Ⅱ.Interpretation in terms of crack-induced anisotropy.Geophys.J.Roy.Astron.Soc.,1985,83(1):75-92.
[4]Crampin S.A review of wave motion in anisotropic andcracked elastic-media.Wave Motion,1981,3(4):343-391.
[5]Crampin S,Volti T,Chastin S,et al.Indication of highpore-fluid pressures in a seismically-active fault zone.Geophys.J.Int.,2002,151(2):F1-F5.
[6]Gao Y,Crampin S.Observations of stress relaxation beforeearthquakes.Geophys.J.Int.,2004,157(2):578-582.
[7]Zatsepin S V,Crampin S.Modelling the compliance of crustalrock—I.Response of shear-wave splitting to differential stress.Geophys.J.Int.,1997,129(3):477-497.
[8]张永久,高原,石玉涛等.四川紫坪铺水库库区地震剪切波分裂研究.地球物理学报,2010,53(9):2091-2101.Zhang Y J,Gao Y,Shi Y T,et al.The shear-wave splittingstudy of Sichuan Zipingpu reservoir region.Chinese J.Geophys.(in Chinese),2010,53(9):2091-2101.
[9]Peng Z G,Ben-Zion Y.Systematic analysis of crustalanisotropy along the Karadere-Duzce branch of the NorthAnatolian fault.Geophys.J.Int.,2004,159(1):253-274.
[10]石玉涛,高原,吴晶等.云南地区地壳介质各向异性——快剪切波偏振特性.地震学报,2006,28(6):574-585.Shi Y T,Gao Y,Wu J,et al.Seismic anisotropy of the crustin Yunnan,China:polarizations of fast shear-waves.ActaSeismologica Sinica(in Chinese),2006,28(6):574-585.
[11]吴晶,高原,陈运泰等.首都圈西北部地区地壳介质地震各向异性特征初步研究.地球物理学报,2007,50(1):209-220.Wu J,Gao Y,Chen Y T,et al.Seismic anisotropy in thecrust in northwestern capital area of China.Chinese J.Geophys.(in Chinese),2007,50(1):209-220.
[12]高原,郑斯华,孙勇.唐山地区地壳裂隙各向异性.地震学报,1995,17(3):283-293.Gao Y,Zheng S H,Sun Y.Crustal crack anisotropy inTangshan.Acta Seismologica Sinica(in Chinese),1995,17(3):283-293.
[13]雷军,王培德,姚陈等.云南剑川近场横波特征及其与构造的关系.地球物理学报,1997,40(6):791-801.Lei J,Wang P D,Yao C,et al.The near-field shear wavesplitting and its relation with structure in Jianchuan,YunnanProvince.Chinese J.Geophys.(in Chinese),1997,40(6):791-801.
[14]周荣军,闻学泽,蔡长星等.甘孜—玉树断裂带的近代地震与未来地震趋势估计.地震地质,1997,19(2):115-124.Zhou R J,Wen X Z,Cai C X,et al.Recent earthquakes andassessment of seismic tendency on the Garzê-Yushu faultzone.Seismology and Geology(in Chinese),1997,19(2):115-124.
[15]中国地震局监测预报司.中国强地震目录(公元前23世纪—公元1999年).北京:中国地震局,1999.Bureau of Monitoring and Prediction,China EarthquakeAdministration.Catalogue of Chinese Strong Earthquakes(23Century B.C.-1999 A.D.)(in Chinese).Beijing:China Earthquake Administration,1999.
[16]唐荣昌,韩渭宾.四川活动断裂与地震.北京:地震出版社,1993.Tang R C,Han W B.Active Faults and Earthquake inSichuan Regional(in Chinese).Beijing:Seismological Press,1993.
[17]闻学泽,黄圣睦,江在雄.甘孜—玉树断裂带的新构造特征与地震危险性估计.地震地质,1985,7(3):23-34.Wen X Z,Huang S M,Jiang Z X.Neotectonic features ofthe Garzê-Yushu fault zone and assessment of its earthquakerisk.Seismology and Geology(in Chinese),1985,7(3):23-34.
[18]彭华,马秀敏,白嘉启等.甘孜—玉树断裂带第四纪活动特征.地质力学学报,2006,12(3):295-304.Peng H,Ma X M,Bai J Q,et al.Characteristics ofQuaternary activities of the Garzê-Yushu fault zone.Journalof Geomechanics(in Chinese),2006,12(3):295-304.
[19]Crampin S,Peacock S.A review of shear-wave splitting inthe compliant crack-critical anisotropic earth.Wave Motion,2005,41(1):59-77.
[20]Menke W,Brandsdottir B,Jakobsdottir S,et al.Seismicanisotropy in the crust at the mid-Atlantic plate boundary insouth-west Iceland.Geophys.J.Int.,1994,119(3):783-790.
[21]Bowman J R,Ando M.Shear-wave splitting in the upper-mantle wedge above the Tonga subduction zone.Geophys.J.Int.,1987,88(1):25-41.
[22]Gao Y,Crampin S.Temporal variations of shear-wavesplitting in field and laboratory studies in China.J.Appl.Geophys.,2003,54(3):279-287.
[23]石玉涛,高原,赵翠萍等.汶川地震余震序列的地震各向异性.地球物理学报,2009,52(2):398-407.Shi Y T,Gao Y,Zhao C P,et al.A study of seismicanisotropy of Wenchuan earthquake sequence.Chinese J.Geophys.(in Chinese),2009,52(2):398-407.
[24]高原,郑斯华,王培德.海南省东方地区1992年小震群剪切波分裂研究.地球物理学报,1996,39(2):221-232.Gao Y,Zheng S H,Wang P D.Shear wave splitting study onsmall earthquake swarm of 1992in Dongfang of Hainan,South China.Chinese J.Geophys.(in Chinese),1996,39(2):221-232.
[25]高原,梁维,丁香等.云南2001年施甸地震的剪切波分裂参数变化特征.地震学报,2004,26(6):576-582.Gao Y,Liang W,Ding X,et al.Variational characteristicsof shear-wave splitting on the 2001Shidian earthquakes inYunnan,China.Acta Seismologica Sinica(in Chinese),2004,26(6):576-582.
[26]Niu F L,Li J.Component azimuths of the CEArray stationsestimated from P-wave particle motion.Earthquake Science,2011,24(1):3-13.
[27]Silver P G,Chan W W.Shear wave splitting andsubcontinental mantle deformation.J.Geophys.Res.,1991,96(B10):16429-16545.
[28]Hudson J A.Wave speeds and attenuation of elastic waves inmaterial containing cracks.Geophys.J.R.Astr.Soc.,1981,64(1):133-150.
[29]庄真,傅竹武,吕梓龄等.青藏高原及邻近地区地壳与上地幔剪切波三维速度结构.地球物理学报,1992,35(6):694-709.Zhuang Z,Fu Z W,LüZ L,et al.3-D shear velocity modelof crust and upper mantle beneath the Tibetan Plateau and itsadjacent regions.Chinese J.Geophys.(in Chinese),1992,35(6):694-709.
[30]Crampin S.The fracture criticality of crustal rocks.Geophys.J.Int.,1994,118(2):428-438.
[31]常利军,丁志峰,王椿镛.2010年玉树7.1级地震震源区横波分裂的变化特征.地球物理学报,2010,53(11):2613-2619.Chang L J,Ding Z F,Wang C Y.Variations of shear wavesplitting in the 2010 Yushu Ms7.1 earthquake region.Chinese J.Geophys.(in Chinese),2010,53(11):2613-2619.
[32]王琪,张培震,牛之俊等.中国大陆现今地壳运动和构造变形.中国科学(D),2001,31(7):529-536.Wang Q,Zhang P Z,Niu Z J,et al.Crustal movement andtectonic deformation of continental China.Science in China(D)(in Chinese),2001,31(7):529-536.
[33]叶正仁,王健.中国大陆现今地壳运动的动力学机制.地球物理学报,2004,47(3):456-461.Ye Z R,Wang J.Dynamics of present-day crustal movementin the China mainland.Chinese J.Geophys.(in Chinese),2004,47(3):456-461.
[34]许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5):492-501.Xu Z H.A present-day tectonic stress map for Eastern Asiaregion.Acta Seismologica Sinica(in Chinese),2001,23(5):492-501.
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