汶川M_S 8.0地震:龙门山断裂两侧地壳各向异性的初步研究
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摘要
利用中国地震局地质研究所地震动力学国家重点实验室在川西地区布设的大规模密集流动宽频带地震台阵记录的远震P波波形数据,分别采用波形互相关和加权叠加方法研究了地壳各向异性。作为初步结果,得到了龙门山断裂两侧4个宽频带流动台站的接收函数莫霍面Ps转换震相快波方向和分裂时间延迟。结果表明:1)波形互相关方法总体上优于方位加权叠加方法,它不但可以给出快波方位,而且可以给出快慢波的时间延迟;方位加权叠加方法测量结果存在不确定性,其原因在于难以确定介质各向异性对称轴的方位;同时采用上述2种不同方法研究地壳各向异性参数有助于判断测量结果的可靠性;2)四川盆地内快波偏振方位基本一致,表明四川盆地地壳整体性较好,横向非均匀变形较弱;3)以汶川地震主震的震中区为界,松潘-甘孜地块北侧快波偏振方位与龙门山断裂近于平行,表明在四川盆地坚硬地壳的阻挡作用下,龙门山断裂附近松潘-甘孜地块北侧可能存在中下地壳软弱物质沿断层向NE方向的扩张变形,而其南侧处于正向挤压的状态。该结果有助于解释汶川MS8.0地震的单侧破裂过程及其余震发育的特征。
From the teleseismic P-waveform data recorded at the dense mega seismic array deployed in the western Sichuan area by the State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,we investigate the crustal anisotropy beneath the stations using waveform correlation method and weighted stacking method. As a preliminary result,we measured the fast polarization azimuth and time delay of the Ps converted wave in the receiver functions at 4 stations on both sides of Longmen Shan Faults. Our results show:1)The waveform correlation method is better than the weighted stacking method and it turns out not only the fast polarization azimuth,but also the time differences between the fast-and slow-wave; The results obtained by using the weighted stacking method are something undetermined due to that the symmetric axis of the crustal anisotropy medium is unclear previously; Application of both methods will be in favor of judging the reliability of the results. 2)The fast polarization azimuths are consistent each other at the stations in Sichuan Basin,suggesting the crust beneath Sichuan Basin has well integrality and a weak lateral deformation. 3)Taking the epicenter of the Wenchuan earthquake as a boundary,the fast polarization azimuth is parallel with the Longmen Shan Faults on the north side of the Sonpan-Ganzi block,and perpendicular to the faults on the south side. This suggests that under the obstruction of the Sichuan Basin,the soft lower crust beneath the north side of the Sonpan-Ganzi block has a NE direction extended deformation along the Longmen Shan Faults,and the crust on its south side is in the status of compressive deformation perpendicular to the faults. Our results can be used for interpreting the single-side rupture of the Wenchuan earthquake and the aftershock evolution.
From the teleseismic P-waveform data recorded at the dense mega seismic array deployed in the western Sichuan area by the State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,we investigate the crustal anisotropy beneath the stations using waveform correlation method and weighted stacking method. As a preliminary result,we measured the fast polarization azimuth and time delay of the Ps converted wave in the receiver functions at 4 stations on both sides of Longmen Shan Faults. Our results show:1)The waveform correlation method is better than the weighted stacking method and it turns out not only the fast polarization azimuth,but also the time differences between the fast-and slow-wave; The results obtained by using the weighted stacking method are something undetermined due to that the symmetric axis of the crustal anisotropy medium is unclear previously; Application of both methods will be in favor of judging the reliability of the results. 2)The fast polarization azimuths are consistent each other at the stations in Sichuan Basin,suggesting the crust beneath Sichuan Basin has well integrality and a weak lateral deformation. 3)Taking the epicenter of the Wenchuan earthquake as a boundary,the fast polarization azimuth is parallel with the Longmen Shan Faults on the north side of the Sonpan-Ganzi block,and perpendicular to the faults on the south side. This suggests that under the obstruction of the Sichuan Basin,the soft lower crust beneath the north side of the Sonpan-Ganzi block has a NE direction extended deformation along the Longmen Shan Faults,and the crust on its south side is in the status of compressive deformation perpendicular to the faults. Our results can be used for interpreting the single-side rupture of the Wenchuan earthquake and the aftershock evolution.
引文
陈九辉,刘启元,李顺成,等.2009.汶川MS8.0地震余震序列重新定位及其地震构造研究[J].地球物理学报,52(2):390—397.CHEN Jiu-hui,LIU Qi-yuan,LI Shun-cheng,et al.2009.Seismotectonic study by relocation of the WenchuanMS8.0earthquake sequence[J].Chinese J Geophys,52(2):390—397(in Chinese).
房立华,吴建平.2009.倾斜界面和各向异性介质对接收函数的影响[J].地球物理学进展,24(1):42—50.FANG Li-hua,WU Jian-ping.2009.Effects of dipping boundaries and anisotropic media on receiver functions[J].Progress in Geophys,24(1):42—50(in Chinese).
赖院根,刘启元,陈九辉,等.2006.首都圈地区横波分裂与地壳应力场特征[J].地球物理学报,49(1):189—196.LAI Yuan-gen,LIU Qi-yuan,CHEN Jiu-hui,et al.2006.Shear wave splitting and the features of the crustal stress fieldin the capital circle[J].Chinese J Geophys,49(1):189—196(in Chinese).
刘启元,陈九辉,李顺成,等.2008.汶川MS8.0地震:川西流动地震台阵观测数据的初步分析[J].地震地质,30(3):584—596.LIU Qi-yuan,CHENJiu-hui,,LI Shun-cheng,et al.2008.TheMS8.0Wenchuan earthquake:Preliminary results fromthe western Sichuan mobile seismic array observations[J].Seismology and Geology,30(3):584—596(in Chi-nese).
刘启元,李昱,陈九辉,等.2009.汶川MS8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,52(2):309—319.LIUQI-yuan,LI Yu,CHENJiu-hui,et al.2009.WenchuanMS8.0earthquake:Preliminary study of the S-wave veloc-ity structure of the crust and upper mantle[J].Chinese J Geophys,52(2):309—319(in Chinese).
李延兴,张静华,周伟,等.2009.汶川MS8.0地震孕育发生的机制和动力学问题[J].地球物理学报,52(2):519—530.LI Yan-xing,ZHANG Jing-hua,ZHOUWei,et al.2009.The mechanism and dynamics of the generation and occurrencefor WenchuanMS8.0earthquake[J].Chinese J Geophys,52(2):519—530(in Chinese).
石玉涛,高原,赵翠萍,等.2009.汶川地震余震序列的地震各向异性[J].地球物理学报,52(2):398—407.SHI Yu-tao,GAO Yuan,ZHAO Cui-ping,et al.2009.Astudy of seismic anisotropy of Wenchuan earthquake sequence[J].Chinese J Geophys,52(2):398—407(in Chinese).
田宝峰,李娟,姚振兴.2008.利用接收函数方位变化研究太行山区地壳各向异性[J].地震学报,30(4):355—366.TIAN Bao-feng,LI Juan,YAO Zhen-xing.2008.A study on crust anisotropy of Taihang Mountain Range by analyzingazimuthal variation of receiver functions[J].Acta Seismologica Sinica,30(4):355—366(in Chinese).
王卫民,赵连锋,李娟.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of theM8.0Wenchuan earthquake of Si-chuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
吴庆举,田小波,张乃铃,等.2003.用Wiener滤波方法提取台站接收函数[J].中国地震,19(1):41—47.WU Qing-ju,TIAN Xiao-bo,ZHANG Nai-ling,et al.2003.Receiver function estimated by Wiener filtering[J].Earthquake Res in China,19(1):41—47(in Chinese).
徐震,徐鸣洁,王良书,等.2006.用接收函数Ps转换波研究地壳各向异性:以哀牢山-红河断裂带为例.[J]地球物理学报,49(2):438—448.XU Zhen,XU Ming-jie,WANG Liang-shu,et al.2006.A study on crustal anisotropy using P to S converted phase ofthe receiver function:Application to Ailaoshan-Red River Fault zone[J].Chinese J Geophys,49(2):438—448(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XUXi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.TheMS8.0Wenchuan earthquake surface ruptures and its seis-mogenic structures[J].Seismology and Geology,30(3):597—629(in Chinese).
姚陈.1989.穿透裂隙介质远震PS波的分裂[J].中国地震,5(1):38—47.YAO Chen.1989.The splitting of the teleseismic PS waves propagating through cracked solids[J].Earthquake Resin China,5(1):38—47(in Chinese).
张永久,高原,石玉涛,等.2008.四川区域地震台网的剪切波分裂研究[J].地震学报,30(2):123—134.ZHANG Yong-jiu,GAO Yuan,SHI Yu-tao,et al.2008.A study on S wave splitting using waveform data from SichuanSeismic Network[J].Acta Seismologica Sinica,30(2):123—134(in Chinese).
Bowman J R,Ando M.1987.Shear-wave splitting in the uppermantle wedge above the Tonga subduction zone[J].Geophys J R Astron Soc,88:25—41.
Burchfiel B C.2003.New technology:New geological challenges[J].Geol Soc Amer Today,14(2):4—10.
Burchfiel B C,Royden L H,Van der Hilst R D,et al.2008.A geological and geophysical context for the Wenchuanearthquake of12May2008,Sichuan,People s Republic of China[J].GSA Today,18(7):4—11.
Casidy J F.1992.Numerical experiments in broadband receiver function analysis[J].Bull Seism Soc Am,82:1453—1474.
Crampin S.1981.Areviewof wave motion in anisotropic and cracked elastic media[J].Wave Motion,3:343—391.
Girardin N,Farra V.1998.Azimuthal anisotropy in the upper mantle from observations of P-to-S converted phases:Application to southeast Australia[J].Geophys J Int,133:615—629.
Kosarev G L,Makeyeva LⅠ,Vinnik L P.1984.Anisotropy of the mantle inferred from observations of P to S conver-ted waves[J].Geophys J R Astr Soc,76:209—220.
Liu Q Y,Chen J H,Li S C.2008.WenchuanMS8.0earthquake:The crustal velocity structure and stress field fromthe western Sichuan seismic array observation[R].AGU Fall Meeting,San Francisco.
McNamara D E,Owens TJ.1993.Azimuthal shear wave velocity anisotropy in the Basin and Range Province using Psconverted phases[J].J Geophys Res,98:12003—12017.
Royden L H,Burchfiel B C,King R W,et al.1997.Surface deformation and lower crustal flow in eastern Tibet[J].Science,276:788—790.
Sandvol E,Hearn T.1994.Bootstrapping shear-wave splitting errors[J].Bull Seism Soc Amer,84(6):1971—1977.
Savage M K,Silver P G.1993.Mantle deformation and tectonics:Constraints from seismic anisotropy in western Unit-ed States[J].Phys Earth Planet Int,78:207—227.
Savage M K.1998.Lower crustal anisotropy or dipping boundaries:Effects on receiver functions and a case study inNew Zealand[J].J Geophys Res,103(B7):15069—15087.
Vecsey L,PlomerováJ,Babu ka V.2008.Shear-wave splitting measurements:Problems and solutions[J].Tectono-physics,462(1-4):178—196.
Vinnik L P,Montagner J P.1996.Shear wave splitting in the mantle Ps phases[J].Geophys Res Lett,23(18):2449—2452.
Wang Y Z,Wang N N,Shen Z K,et al.2008.GPS-constrained inversion of present-day slip rates along major faults ofthe Sichuan-Yunnan region,China[J].Science in China(Ser D),51(9):1267—1283.
房立华,吴建平.2009.倾斜界面和各向异性介质对接收函数的影响[J].地球物理学进展,24(1):42—50.FANG Li-hua,WU Jian-ping.2009.Effects of dipping boundaries and anisotropic media on receiver functions[J].Progress in Geophys,24(1):42—50(in Chinese).
赖院根,刘启元,陈九辉,等.2006.首都圈地区横波分裂与地壳应力场特征[J].地球物理学报,49(1):189—196.LAI Yuan-gen,LIU Qi-yuan,CHEN Jiu-hui,et al.2006.Shear wave splitting and the features of the crustal stress fieldin the capital circle[J].Chinese J Geophys,49(1):189—196(in Chinese).
刘启元,陈九辉,李顺成,等.2008.汶川MS8.0地震:川西流动地震台阵观测数据的初步分析[J].地震地质,30(3):584—596.LIU Qi-yuan,CHENJiu-hui,,LI Shun-cheng,et al.2008.TheMS8.0Wenchuan earthquake:Preliminary results fromthe western Sichuan mobile seismic array observations[J].Seismology and Geology,30(3):584—596(in Chi-nese).
刘启元,李昱,陈九辉,等.2009.汶川MS8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,52(2):309—319.LIUQI-yuan,LI Yu,CHENJiu-hui,et al.2009.WenchuanMS8.0earthquake:Preliminary study of the S-wave veloc-ity structure of the crust and upper mantle[J].Chinese J Geophys,52(2):309—319(in Chinese).
李延兴,张静华,周伟,等.2009.汶川MS8.0地震孕育发生的机制和动力学问题[J].地球物理学报,52(2):519—530.LI Yan-xing,ZHANG Jing-hua,ZHOUWei,et al.2009.The mechanism and dynamics of the generation and occurrencefor WenchuanMS8.0earthquake[J].Chinese J Geophys,52(2):519—530(in Chinese).
石玉涛,高原,赵翠萍,等.2009.汶川地震余震序列的地震各向异性[J].地球物理学报,52(2):398—407.SHI Yu-tao,GAO Yuan,ZHAO Cui-ping,et al.2009.Astudy of seismic anisotropy of Wenchuan earthquake sequence[J].Chinese J Geophys,52(2):398—407(in Chinese).
田宝峰,李娟,姚振兴.2008.利用接收函数方位变化研究太行山区地壳各向异性[J].地震学报,30(4):355—366.TIAN Bao-feng,LI Juan,YAO Zhen-xing.2008.A study on crust anisotropy of Taihang Mountain Range by analyzingazimuthal variation of receiver functions[J].Acta Seismologica Sinica,30(4):355—366(in Chinese).
王卫民,赵连锋,李娟.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-min,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of theM8.0Wenchuan earthquake of Si-chuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
吴庆举,田小波,张乃铃,等.2003.用Wiener滤波方法提取台站接收函数[J].中国地震,19(1):41—47.WU Qing-ju,TIAN Xiao-bo,ZHANG Nai-ling,et al.2003.Receiver function estimated by Wiener filtering[J].Earthquake Res in China,19(1):41—47(in Chinese).
徐震,徐鸣洁,王良书,等.2006.用接收函数Ps转换波研究地壳各向异性:以哀牢山-红河断裂带为例.[J]地球物理学报,49(2):438—448.XU Zhen,XU Ming-jie,WANG Liang-shu,et al.2006.A study on crustal anisotropy using P to S converted phase ofthe receiver function:Application to Ailaoshan-Red River Fault zone[J].Chinese J Geophys,49(2):438—448(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629.XUXi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.TheMS8.0Wenchuan earthquake surface ruptures and its seis-mogenic structures[J].Seismology and Geology,30(3):597—629(in Chinese).
姚陈.1989.穿透裂隙介质远震PS波的分裂[J].中国地震,5(1):38—47.YAO Chen.1989.The splitting of the teleseismic PS waves propagating through cracked solids[J].Earthquake Resin China,5(1):38—47(in Chinese).
张永久,高原,石玉涛,等.2008.四川区域地震台网的剪切波分裂研究[J].地震学报,30(2):123—134.ZHANG Yong-jiu,GAO Yuan,SHI Yu-tao,et al.2008.A study on S wave splitting using waveform data from SichuanSeismic Network[J].Acta Seismologica Sinica,30(2):123—134(in Chinese).
Bowman J R,Ando M.1987.Shear-wave splitting in the uppermantle wedge above the Tonga subduction zone[J].Geophys J R Astron Soc,88:25—41.
Burchfiel B C.2003.New technology:New geological challenges[J].Geol Soc Amer Today,14(2):4—10.
Burchfiel B C,Royden L H,Van der Hilst R D,et al.2008.A geological and geophysical context for the Wenchuanearthquake of12May2008,Sichuan,People s Republic of China[J].GSA Today,18(7):4—11.
Casidy J F.1992.Numerical experiments in broadband receiver function analysis[J].Bull Seism Soc Am,82:1453—1474.
Crampin S.1981.Areviewof wave motion in anisotropic and cracked elastic media[J].Wave Motion,3:343—391.
Girardin N,Farra V.1998.Azimuthal anisotropy in the upper mantle from observations of P-to-S converted phases:Application to southeast Australia[J].Geophys J Int,133:615—629.
Kosarev G L,Makeyeva LⅠ,Vinnik L P.1984.Anisotropy of the mantle inferred from observations of P to S conver-ted waves[J].Geophys J R Astr Soc,76:209—220.
Liu Q Y,Chen J H,Li S C.2008.WenchuanMS8.0earthquake:The crustal velocity structure and stress field fromthe western Sichuan seismic array observation[R].AGU Fall Meeting,San Francisco.
McNamara D E,Owens TJ.1993.Azimuthal shear wave velocity anisotropy in the Basin and Range Province using Psconverted phases[J].J Geophys Res,98:12003—12017.
Royden L H,Burchfiel B C,King R W,et al.1997.Surface deformation and lower crustal flow in eastern Tibet[J].Science,276:788—790.
Sandvol E,Hearn T.1994.Bootstrapping shear-wave splitting errors[J].Bull Seism Soc Amer,84(6):1971—1977.
Savage M K,Silver P G.1993.Mantle deformation and tectonics:Constraints from seismic anisotropy in western Unit-ed States[J].Phys Earth Planet Int,78:207—227.
Savage M K.1998.Lower crustal anisotropy or dipping boundaries:Effects on receiver functions and a case study inNew Zealand[J].J Geophys Res,103(B7):15069—15087.
Vecsey L,PlomerováJ,Babu ka V.2008.Shear-wave splitting measurements:Problems and solutions[J].Tectono-physics,462(1-4):178—196.
Vinnik L P,Montagner J P.1996.Shear wave splitting in the mantle Ps phases[J].Geophys Res Lett,23(18):2449—2452.
Wang Y Z,Wang N N,Shen Z K,et al.2008.GPS-constrained inversion of present-day slip rates along major faults ofthe Sichuan-Yunnan region,China[J].Science in China(Ser D),51(9):1267—1283.
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