1999年台湾集集地震余震区——嘉义地区地震的剪切波分裂参数随时间变化的研究
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摘要
本文利用台湾中央气象局布设的嘉义台CHY、民雄台CHN2和义竹台CHN8记录的地震波形资料,使用波形互相关的SAM分析方法(剪切波分裂系统分析方法),对发生在1999年9月20日台湾集集大地震(MW7.6)余震区的嘉义ML6.4和ML6.0级地震的震前序列,开展了长达22个月的大震前近场源剪切波分裂参数随时间变化的应力预测研究.研究结果表明,在正常情况下,快剪切波的偏振方向大致近东西向,与嘉义地区最大主压应力场的方向一致,表明该区的各向异性受区域构造应力场控制;根据剪切波分裂参数——快剪切波偏振方向和慢剪切波时间延迟随时间的变化,我们认为,临震期慢剪切波时间延迟的快速下降和快剪切波偏振方向90°跳跃事件的频繁发生,可以作为临震期大震应力预测的前兆指标.近场源剪切波分裂参数随时间的变化在揭示震源区应力变化方面将发挥重大作用.
Based on the data from three seismic stations CHY, CHN2 and CHN8 of Taiwan Central Weather Bureau Seismic Network (CWBSN), the systematic analysis method (SAM) of shear-wave splitting has been used to do the near-source stress-forecast research of temporal preseismic variations of polarization directions and time delays in nearly 22 months before 1999 M_L 6.4 and M_L 6.0 earthquakes in the Chiayi area, the aftershock zone of M_W7.6 Chichi, Taiwan earthquake of September 20, 1999. The result shows that the normal polarization directions of station CHY, CHN2 and CHN8 are approximately EW, in good agreement with the direction of maximum compressional stress, suggesting that the anisotropy in this area is controlled by local tectonic stress field. The results strongly indicate that in the stress critical stage, the polarization 90°-flips occurred frequently, and that there were abrupt decreases in time delays shortly before the Chichi mainshock and two Chiayi earthquakes. These can be considered as two precursors of stress-forecast. We think that the temporal variations of shear-wave splitting are of great importance, since they provide information about source stress processes and critical warning information before large earthquakes.
Based on the data from three seismic stations CHY, CHN2 and CHN8 of Taiwan Central Weather Bureau Seismic Network (CWBSN), the systematic analysis method (SAM) of shear-wave splitting has been used to do the near-source stress-forecast research of temporal preseismic variations of polarization directions and time delays in nearly 22 months before 1999 M_L 6.4 and M_L 6.0 earthquakes in the Chiayi area, the aftershock zone of M_W7.6 Chichi, Taiwan earthquake of September 20, 1999. The result shows that the normal polarization directions of station CHY, CHN2 and CHN8 are approximately EW, in good agreement with the direction of maximum compressional stress, suggesting that the anisotropy in this area is controlled by local tectonic stress field. The results strongly indicate that in the stress critical stage, the polarization 90°-flips occurred frequently, and that there were abrupt decreases in time delays shortly before the Chichi mainshock and two Chiayi earthquakes. These can be considered as two precursors of stress-forecast. We think that the temporal variations of shear-wave splitting are of great importance, since they provide information about source stress processes and critical warning information before large earthquakes.
引文
[1]Crampin S.Seismic wave propagation through a cracked solid:polarization as possible dilatancy diagnostic.Geophys.J.R.Astr.Soc.,1978,53:467~496
[2]Zatsepin S V,Crampin S.Modellingthe compliance of crustal rock:I.Response of shear-wave splitting to differential stress.Geophys.J.Int.,1997,129:477~494
[3]Crampin S,Zatsepin S V.Modelingthe compliance of crustal rock:Ⅱ.Response to temporal changes before earthquake.Geophys.J.Int.,1997,129:495~506
[4]Peacock S,Crampin S,Booth DC,et al.Shear wave splittinginthe Anza seismic gap,southern California:temporal variations as possible precursors.J.Geophys.Res.,1988,93:3339~3356
[5]Booth DC,Crampin S,Lovell J H,et al.Temporal changesinshear wave splitting duringanearthquake swarmin Arkansas.J.Geophys.Res.,1990,95:11151~11164
[6]Gao Y,Crampin S.Temporal variations of shear-wave splitting in field and laboratory studies in China.J.Appl.Geophys.,2003,54:279~287
[7]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):221~232Gao Y,Zheng S H,Wang P D.Research of the shear wave splitting at swarm of small earthquakes in1992near Dongfang,HainanIsland.Chinese J.Geophys.(in Chinese),1996,39(2):221~232
[8]Crampin S,Booth D C,Evans R,et al.Changes in shear wave splitting at Anza near the time of the North Palmsprings earthquake.J.Geophys.Res.,1990,95:11197~11212
[9]Crampin S,Booth D C,Evans R,et al.Comment on“Quantitative measurements of shear wave polarizations at the Anza seismic network,southern California:implications for shear wave splitting and earthquake prediction,by R.C.Aster,P.M.Shearer and J.Berger”.J.Geophys.Res.,1991,96:6403~6414
[10]Liu Y,Crampin S,Main I.Shear-wave anisotropy:spatial and temporal variations in time delays at Parkfield,Central California.Geophys.J.Int.,1997,130:771~785
[11]Volti T,Crampin S.Afour-year study of shear-wave splitting in Iceland:1.Background and preliminary analysis.In:Nieuwland,D.A.(Ed.),New insights into structural interpretation and modelling.Geol.Soc.Lond.,Spec.Publ.,2003,212:117~133
[12]Volti T,Crampin S.Afour-year study of shear-wave splitting in Iceland:2.Temporal changes before earthquakes and volcanic eruptions.In:Nieuwland D A ed.New insights into structural interpretation and modelling.Geol.Soc.Lond.,Spec.Publ.,2003,212:135~149
[13]Crampin S.Stress-forecasting:a viable alternative to earthquake predictionin dynamic Earth.Trans.R.Soc.Edin.,Earth Sci.,1998,89:121~133
[14]Crampin S,Volti T,Stef偄nsson R.A successfully stressforecast earthquake.Geophys.J.Int.,1999,138:F1~F5
[15]WuJ,Crampin S,Gao Y,Hao P,Volti T,Chen Y T.Smaller source earthquakes and improved measuring techniques allow the largest earthquakes in Icelandto be stress forecast(with hindsight).Geophys.J.Int.,2006,166:1293~1298
[16]Crampin S,Peacock S,Gao Y,et al.The scatter of time delays in shear-wave splitting above small earthquakes.Geophys.J.Int.,2004,156:39~44
[17]Crampin S,Zatsepin S V,Slater C,et al.Abnormal shear-wave polarizations as indicators of pressures and over pressures.In:58th Conf.,EAGE,Amsterdam,Extended Abstracts,1996,X038
[18]Angerer E,Crampin S,Li X Y,et al.Processing,modelling,and predicting time-lapse effects of overpressured fluid-injection in a fractured reservoir.Geophys.J.Int.,2003,149:267~280
[19]Crampin S,Chastin S,Gao Y.Shear-wave splitting in a critical crust:Ⅲ.Preliminary report of multi-variable measurements in active tectonics.J.Appl.Geophys.,2003,54:265~277
[20]Tadokoro K,Ando M.Evidence for rapid fault healing derived from temporal changes in S wave splitting.Geophys.Res.Lett.,2002,29:1047~1050
[21]Miller V,Savage M.Changes in seismic anisotropy after volcanic eruptions:evidence from Mount Ruapehu.Science,2001,293:2231~2233
[22]Padhy S,Crampin S.High pore-fluid pressures at Bhuj,inferred from90°-flips in shear-wave polarizations.Geophys.J.Int.,2006,164:370~376
[23]Crampin S,Volti T,Chastin S,et al.Indication of high pore-fluid pressures in a seismically-active fault zone.Geophys.J.Int.,2002,151:F1~F5
[24]高原,郑斯华,周蕙兰.唐山地区快剪切波偏振图像及其变化.地球物理报,1999,42(2):228~232Gao Y,Zheng S H,Zhou HL.Polarization patterns of fast shear wave in Tangshan region and their variations.Chinese J.Geophys.(in Chinese),1999,42(2):228~232
[25]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):209~220Wu J,Gao Y,Chen YT,et al.Seismic anisotropy in the crust in northwestern capital area of China.Chinese J.Geophys.(in Chinese),2007,50(1):209~220
[26]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):189~196Lai Y G,Liu Q Y,Chen J H,et al.Shear wave splitting and the features of the crustal stress field in the Capital circle.Chinese J.Geophys.(in Chinese),2006,49(1):189~196
[27]赖院根,刘启元,陈九辉等.新疆伽师强震群区的横波分裂与应力场特征.地球物理学报,2002,45(1):83~92Lai Y G,Liu Q Y,Chen J H,et al.Features of the S-wave splitting and stress field in the Xinjiang Jiashi strong earthquake region.Chinese J.Geophys.(in Chinese),2002,45(1):83~92
[28]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):791~801Lei J,Wang P D,Yao C,et al.Near field shear wave characteristics andits relation with structure in Jianchuan,Yunnan.Chinese J.Geophys.(in Chinese),1997,40(6):791~801
[29]Gao Y,Crampin S.Observations of stress relaxation before earthquakes.Geophys.J.Int.,2004,157:578~582
[30]高原,李世愚,周蕙兰等.大理岩的剪切波分裂对差应力变化响应的实验研究.地球物理学报,1999,42(6):778~784Gao Y,Li S Y,Zhou HL,et al.Experimental studies of marbles on response of shear-wave splitting to differential stress variation.Chinese J.Geophys(in Chinese),1999,42(6):778~784
[31]Yu S B.Microearthquake activity in southwestern Taiwan.Bull.of the Ins.ofEarth Science,Academia Sinica,1983,3:71~86
[32]Omori F.Preliminary note on the Formosa earthquake of March17,1906.Imp.Earthquake Inves.Comm.Bull.,1907,2:53~71
[33]Yu S B,Kuo L C,Hsu Y J,et al.Preseismic deformation and coseismic displacements associated withthe1999Chi-Chi,Taiwan,earthquake.Bull.Seism.Soc.Am.,2001,91:995~1012
[34]高原,刘希强,梁维等.剪切波分裂系统分析方法(SAM)软件系统.中国地震,2004,20(1):101~107Gao Y,Liu X Q,Liang W,et al.Systematic analysis method of shear-wave splitting:SAMsoftware system.Earthquake Research in China(in Chinese),2004,20(1):101~107
[35]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):576~582Gao Y,Liang W,Ding X,et al.Variational characteristics of shear-wave splitting on the2001Shidian earthquakes in Yunnan,China.Acta Seismologica Sinica(in Chinese),2004,26(6):576~582
[36]Rau RJ,Liang WZ,Kao H,et al.Shear wave anisotropy beneath the Taiwan orogen.Earth Planet.Sci.Leitt.,2000,177:177~192
[37]Shih X R,Meyer RP,Schneider J F.An automated and analytical method to determine shear wave splitting.Tectonophysics,1989,165:271~278
[38]Chen C H,Yen HJ.Apreliminarystudy on crustal anisotropy Chia-Nan area of Taiwan.Terrestrial Atmospheric and Oceanic Sciences,1998,9:573~588
[2]Zatsepin S V,Crampin S.Modellingthe compliance of crustal rock:I.Response of shear-wave splitting to differential stress.Geophys.J.Int.,1997,129:477~494
[3]Crampin S,Zatsepin S V.Modelingthe compliance of crustal rock:Ⅱ.Response to temporal changes before earthquake.Geophys.J.Int.,1997,129:495~506
[4]Peacock S,Crampin S,Booth DC,et al.Shear wave splittinginthe Anza seismic gap,southern California:temporal variations as possible precursors.J.Geophys.Res.,1988,93:3339~3356
[5]Booth DC,Crampin S,Lovell J H,et al.Temporal changesinshear wave splitting duringanearthquake swarmin Arkansas.J.Geophys.Res.,1990,95:11151~11164
[6]Gao Y,Crampin S.Temporal variations of shear-wave splitting in field and laboratory studies in China.J.Appl.Geophys.,2003,54:279~287
[7]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):221~232Gao Y,Zheng S H,Wang P D.Research of the shear wave splitting at swarm of small earthquakes in1992near Dongfang,HainanIsland.Chinese J.Geophys.(in Chinese),1996,39(2):221~232
[8]Crampin S,Booth D C,Evans R,et al.Changes in shear wave splitting at Anza near the time of the North Palmsprings earthquake.J.Geophys.Res.,1990,95:11197~11212
[9]Crampin S,Booth D C,Evans R,et al.Comment on“Quantitative measurements of shear wave polarizations at the Anza seismic network,southern California:implications for shear wave splitting and earthquake prediction,by R.C.Aster,P.M.Shearer and J.Berger”.J.Geophys.Res.,1991,96:6403~6414
[10]Liu Y,Crampin S,Main I.Shear-wave anisotropy:spatial and temporal variations in time delays at Parkfield,Central California.Geophys.J.Int.,1997,130:771~785
[11]Volti T,Crampin S.Afour-year study of shear-wave splitting in Iceland:1.Background and preliminary analysis.In:Nieuwland,D.A.(Ed.),New insights into structural interpretation and modelling.Geol.Soc.Lond.,Spec.Publ.,2003,212:117~133
[12]Volti T,Crampin S.Afour-year study of shear-wave splitting in Iceland:2.Temporal changes before earthquakes and volcanic eruptions.In:Nieuwland D A ed.New insights into structural interpretation and modelling.Geol.Soc.Lond.,Spec.Publ.,2003,212:135~149
[13]Crampin S.Stress-forecasting:a viable alternative to earthquake predictionin dynamic Earth.Trans.R.Soc.Edin.,Earth Sci.,1998,89:121~133
[14]Crampin S,Volti T,Stef偄nsson R.A successfully stressforecast earthquake.Geophys.J.Int.,1999,138:F1~F5
[15]WuJ,Crampin S,Gao Y,Hao P,Volti T,Chen Y T.Smaller source earthquakes and improved measuring techniques allow the largest earthquakes in Icelandto be stress forecast(with hindsight).Geophys.J.Int.,2006,166:1293~1298
[16]Crampin S,Peacock S,Gao Y,et al.The scatter of time delays in shear-wave splitting above small earthquakes.Geophys.J.Int.,2004,156:39~44
[17]Crampin S,Zatsepin S V,Slater C,et al.Abnormal shear-wave polarizations as indicators of pressures and over pressures.In:58th Conf.,EAGE,Amsterdam,Extended Abstracts,1996,X038
[18]Angerer E,Crampin S,Li X Y,et al.Processing,modelling,and predicting time-lapse effects of overpressured fluid-injection in a fractured reservoir.Geophys.J.Int.,2003,149:267~280
[19]Crampin S,Chastin S,Gao Y.Shear-wave splitting in a critical crust:Ⅲ.Preliminary report of multi-variable measurements in active tectonics.J.Appl.Geophys.,2003,54:265~277
[20]Tadokoro K,Ando M.Evidence for rapid fault healing derived from temporal changes in S wave splitting.Geophys.Res.Lett.,2002,29:1047~1050
[21]Miller V,Savage M.Changes in seismic anisotropy after volcanic eruptions:evidence from Mount Ruapehu.Science,2001,293:2231~2233
[22]Padhy S,Crampin S.High pore-fluid pressures at Bhuj,inferred from90°-flips in shear-wave polarizations.Geophys.J.Int.,2006,164:370~376
[23]Crampin S,Volti T,Chastin S,et al.Indication of high pore-fluid pressures in a seismically-active fault zone.Geophys.J.Int.,2002,151:F1~F5
[24]高原,郑斯华,周蕙兰.唐山地区快剪切波偏振图像及其变化.地球物理报,1999,42(2):228~232Gao Y,Zheng S H,Zhou HL.Polarization patterns of fast shear wave in Tangshan region and their variations.Chinese J.Geophys.(in Chinese),1999,42(2):228~232
[25]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):209~220Wu J,Gao Y,Chen YT,et al.Seismic anisotropy in the crust in northwestern capital area of China.Chinese J.Geophys.(in Chinese),2007,50(1):209~220
[26]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):189~196Lai Y G,Liu Q Y,Chen J H,et al.Shear wave splitting and the features of the crustal stress field in the Capital circle.Chinese J.Geophys.(in Chinese),2006,49(1):189~196
[27]赖院根,刘启元,陈九辉等.新疆伽师强震群区的横波分裂与应力场特征.地球物理学报,2002,45(1):83~92Lai Y G,Liu Q Y,Chen J H,et al.Features of the S-wave splitting and stress field in the Xinjiang Jiashi strong earthquake region.Chinese J.Geophys.(in Chinese),2002,45(1):83~92
[28]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):791~801Lei J,Wang P D,Yao C,et al.Near field shear wave characteristics andits relation with structure in Jianchuan,Yunnan.Chinese J.Geophys.(in Chinese),1997,40(6):791~801
[29]Gao Y,Crampin S.Observations of stress relaxation before earthquakes.Geophys.J.Int.,2004,157:578~582
[30]高原,李世愚,周蕙兰等.大理岩的剪切波分裂对差应力变化响应的实验研究.地球物理学报,1999,42(6):778~784Gao Y,Li S Y,Zhou HL,et al.Experimental studies of marbles on response of shear-wave splitting to differential stress variation.Chinese J.Geophys(in Chinese),1999,42(6):778~784
[31]Yu S B.Microearthquake activity in southwestern Taiwan.Bull.of the Ins.ofEarth Science,Academia Sinica,1983,3:71~86
[32]Omori F.Preliminary note on the Formosa earthquake of March17,1906.Imp.Earthquake Inves.Comm.Bull.,1907,2:53~71
[33]Yu S B,Kuo L C,Hsu Y J,et al.Preseismic deformation and coseismic displacements associated withthe1999Chi-Chi,Taiwan,earthquake.Bull.Seism.Soc.Am.,2001,91:995~1012
[34]高原,刘希强,梁维等.剪切波分裂系统分析方法(SAM)软件系统.中国地震,2004,20(1):101~107Gao Y,Liu X Q,Liang W,et al.Systematic analysis method of shear-wave splitting:SAMsoftware system.Earthquake Research in China(in Chinese),2004,20(1):101~107
[35]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):576~582Gao Y,Liang W,Ding X,et al.Variational characteristics of shear-wave splitting on the2001Shidian earthquakes in Yunnan,China.Acta Seismologica Sinica(in Chinese),2004,26(6):576~582
[36]Rau RJ,Liang WZ,Kao H,et al.Shear wave anisotropy beneath the Taiwan orogen.Earth Planet.Sci.Leitt.,2000,177:177~192
[37]Shih X R,Meyer RP,Schneider J F.An automated and analytical method to determine shear wave splitting.Tectonophysics,1989,165:271~278
[38]Chen C H,Yen HJ.Apreliminarystudy on crustal anisotropy Chia-Nan area of Taiwan.Terrestrial Atmospheric and Oceanic Sciences,1998,9:573~588
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