广西龙滩库区地震剪切波分裂研究
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摘要
利用在龙滩地震观测台网2009年4月至2010年4月记录到的16,452条地震波形数据,采用传统的相关系数法和偏振分析方法,对龙滩库区剪切波分裂特征进行了系统的研究,并讨论了库区范围介质的各向异性特征。研究发现,库区较大区域内地震台站附近的偏振方向主要反映了区域整体应力场的作用方向,但局部构造和断层会控制或影响台站的快剪切波偏振优势方向。归一化1km单位距离上的延迟时间为10～25ms/km,其中距离库坝区较远、水深较浅、蓄水后响应地震活动相对较弱的LIL和XIL台单位距离上的延迟时间在10ms/km左右,而其他台站尤其库坝区附近蓄水后水深较深的则在20ms/km左右,这表明了库水渗透或载荷对库区裂隙状态的影响。研究还发现DPD和GAL台的快慢波延迟时间随水位变化而出现变化,其变化趋势呈现出与水位变化形态基本一致的现象,初步认为是与库区蓄水加载引起的裂隙进水扩张有关。
In this paper,the shear wave splitting features in Longtan reservoir area are studied by adopting the traditional cross-correlation coefficient method and polarization analysis,using the data recorded by the seismic network founded by a project under the National Science and Technology Pillar Program from April 2009 to April 2010.We found that most of polarization directions at seismic stations are consistent with the direction of the overall regional stress field,but local structures and faults may control or influence the fast shear-wave polarization direction.The time-delay normalized to source-station path is between 10 to 25ms/km,and among them,the time-delay is about 10ms/km at the stations LIL and XIL,which are farther away from the dam.The water depth is relatively shallow and seismic activity relatively weak after water storage,indicating the effect of reservoir water penetration or loading on the state of cracks in the reservoir area.We also found that the delay time changes consistently with the water level at stations DPD and GAL.It may be related to crack expansion and water penetration caused by the reservoir impoundment.
In this paper,the shear wave splitting features in Longtan reservoir area are studied by adopting the traditional cross-correlation coefficient method and polarization analysis,using the data recorded by the seismic network founded by a project under the National Science and Technology Pillar Program from April 2009 to April 2010.We found that most of polarization directions at seismic stations are consistent with the direction of the overall regional stress field,but local structures and faults may control or influence the fast shear-wave polarization direction.The time-delay normalized to source-station path is between 10 to 25ms/km,and among them,the time-delay is about 10ms/km at the stations LIL and XIL,which are farther away from the dam.The water depth is relatively shallow and seismic activity relatively weak after water storage,indicating the effect of reservoir water penetration or loading on the state of cracks in the reservoir area.We also found that the delay time changes consistently with the water level at stations DPD and GAL.It may be related to crack expansion and water penetration caused by the reservoir impoundment.
引文
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太龄雪,高原,石玉涛,等.2009.辽宁区域地震台网的地壳剪切波分裂研究[J].地震地质,31(3):357—371.TAI Ling-xue,GAO Yuan,SHI Yu-tao,et al.2009.A study of shear wave splitting in the crust by Liaoning telemetryseismic network of China[J].Seismology and Geology,31(3):357—371(in Chinese).
杨清源,胡毓良,陈献程,等.1996.国内外水库诱发地震目录[J].地震地质,18(4):454—461.YANG Qing-yuan,HU Yu-liang,CHEN Xian-cheng,et al.1996.Catalogue of reservoir induced seismicity events in theworld[J].Seismology and Geology,18(4):454—461(in Chinese).
Booth D C,Crampin S.1985.Shear-wave polarizations on a curved wavefront at an isotropic free surface[J].Geophys JR Astr Soc,83:31—45.
Cochran E S,Vidale J E,Li Y G.2003.Near fault anisotropy following the Hector Mine earthquake[J].J GeophysRes,108(B9):2436—2447.
Crampin S.1978.Seismic-wave propagation through a cracked solid polarization as a possible dilatancy diagnostic[J].Geophys J R Astron Soc,53:467—496.
Crampin S.1981.A review of wave motion in an isotropic and cracked elastic media[J].Wave Motion,3:343—391.
Maya Elkibbi,Rial J A.2005.The Geysers geothermal field:Results from shear-wave splitting analysis in a fracturedreservoir[J].Geophys J Int,162:1024—1035.
Nuttli O.1961.The effect of earth s surface on the S-wave particle motion[J].Bull Seism Soc Amer,51:237—246.
Peng Z,Ben Zion Y.2004.Systematic analysis of crustal anisotropy along the Karadere-Duzce branch of the North Ana-tolian Fault[J].Geophys J lnt,159:253—274.
Saikai A,Yoshihiro H,Toru O,et al.2003.Spatial variation in the crustal anisotropy and its temporal variation associat-ed with a moderate-sized earthquake in the Tokai region,central Japan[J].Geophys JⅠ,154:695—705.
Shih X R,Meyer R P.1990.Observation of shear wave splitting from nature events:south moat of Long Valley caldera,California,June29to August12,1982[J].J Geophys Res,95:11179—11196.
郭培兰,姚宏,袁媛.2006.龙滩水库地震危险性分析[J].高原地震,18(4):17—23.GUO Pei-lan,YAO Hong,YUAN Yuan.2006.Analysis on potential seismic risk in Longtan reservoir[J].PlateauEarthquake Research,18(4):17—23(in Chinese).
高原,藤吉文.2005.中国大陆地壳与上地幔地震各向异性研究[J].地球物理学进展,20(1):180—185.GAO Yuan,TENG Ji-wen.2005.Studies on seismic anisotropy in the crust and mantle on Chinese mainland[J].Pro-gress in Geophysics,20(1):180—185(in Chinese).
高原,吴晶.2008.利用剪切波各向异性推断地壳主压应力场:以首都圈地区为例[J].科学通报,53(23):2933—2939.GAO Yuan,WUJing.2008.Deducing the crustal principal compressive stress using shear wave anisotropy:Acase stud-y in the Capital Circle Region[J].Chinese Science Bulletin,53(23):2933—2939(in Chinese).
高原,郑斯华,周蕙兰.1999.唐山地区快剪切波偏振图像及其变化[J].地球物理学报,42(2):228—232.GAO Yuan,ZHENG Si-hua,ZHOUHui-lan.1999.Polarization patterns of fast shear wave in Tangshan region and theirvariations.[J].Chinese Journal of Geophysics,42(2):228—232(in Chinese).
高原,郑斯华,孙勇.1995.唐山地区地壳裂隙各向异性[J].地震学报,17(3):283—293.GAO Yuan,ZHENG Si-hua,SUN Yong.1995.Crustal crack anisotropy in Tangshan[J].Acta Seismologica Sinica,17(3):283—293(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 Journal of Geophysics,49(1):189—196(in Chinese).
太龄雪,高原,石玉涛,等.2009.辽宁区域地震台网的地壳剪切波分裂研究[J].地震地质,31(3):357—371.TAI Ling-xue,GAO Yuan,SHI Yu-tao,et al.2009.A study of shear wave splitting in the crust by Liaoning telemetryseismic network of China[J].Seismology and Geology,31(3):357—371(in Chinese).
杨清源,胡毓良,陈献程,等.1996.国内外水库诱发地震目录[J].地震地质,18(4):454—461.YANG Qing-yuan,HU Yu-liang,CHEN Xian-cheng,et al.1996.Catalogue of reservoir induced seismicity events in theworld[J].Seismology and Geology,18(4):454—461(in Chinese).
Booth D C,Crampin S.1985.Shear-wave polarizations on a curved wavefront at an isotropic free surface[J].Geophys JR Astr Soc,83:31—45.
Cochran E S,Vidale J E,Li Y G.2003.Near fault anisotropy following the Hector Mine earthquake[J].J GeophysRes,108(B9):2436—2447.
Crampin S.1978.Seismic-wave propagation through a cracked solid polarization as a possible dilatancy diagnostic[J].Geophys J R Astron Soc,53:467—496.
Crampin S.1981.A review of wave motion in an isotropic and cracked elastic media[J].Wave Motion,3:343—391.
Maya Elkibbi,Rial J A.2005.The Geysers geothermal field:Results from shear-wave splitting analysis in a fracturedreservoir[J].Geophys J Int,162:1024—1035.
Nuttli O.1961.The effect of earth s surface on the S-wave particle motion[J].Bull Seism Soc Amer,51:237—246.
Peng Z,Ben Zion Y.2004.Systematic analysis of crustal anisotropy along the Karadere-Duzce branch of the North Ana-tolian Fault[J].Geophys J lnt,159:253—274.
Saikai A,Yoshihiro H,Toru O,et al.2003.Spatial variation in the crustal anisotropy and its temporal variation associat-ed with a moderate-sized earthquake in the Tokai region,central Japan[J].Geophys JⅠ,154:695—705.
Shih X R,Meyer R P.1990.Observation of shear wave splitting from nature events:south moat of Long Valley caldera,California,June29to August12,1982[J].J Geophys Res,95:11179—11196.
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