汶川M_W 7.9和集集M_W 7.6地震前应力场转换现象及其可能的前兆意义
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摘要
2008年四川汶川M_W 7.9地震和1999年台湾集集M_W7.6地震均为挤压推覆构造环境下发生的板内逆断层型地震.通过对比分析2次地震前的CMT解、震源区附近的中小地震震源机制解及其反演的应力场可知,集集地震主震震源机制解与用台湾内陆中西部的CMT解反演得到的逆断层类型构造应力场吻合,而在主震前震源区附近中小地震震源机制解反演得到与构造应力场不一致的走滑类型局部应力场,但当局部应力场变化到与构造应力场一致时,数月后发生主震;同样,用青藏高原东部的CMT解震源机制反演得到走滑类型的构造应力场,逆断层类型的汶川主震与构造应力场的压应力轴吻合,震区附近中小地震反演得到了与构造应力场一致的区域应力场,但震前局部应力场变化与逆断层类型应力场一致时,随即发生主震.说明逆断层型主震区附近随着震源区应力积累,在震前会出现相似的局部应力场转换现象,当最终转换到与发生主震的应力状态一致时,表明震源区附近应力已达到相当高的应力水平,可能是发生大地震的征兆,应引起进一步的关注.
The 2008 Wenchuan earthquake and the 1999 Chi-Chi earthquake are both intraplate thrust fault earthquakes occurred under the tectonic setting of thrust-nappe.Through comparative analysis on CMT solutions,focal mechanism solutions of small and moderate earthquakes,and tectonic stress field near the mainshock region,we found that the thrust type focal mechanism of the Chi-Chi mainshock coincides with the tectonic stress field derived from the CMT solutions of earthquakes occurred in Taiwan central and western inland;but the small and moderate earthquakes randomly occurred near mainshock region resulted in strike slip type focal mechanisms,indicating the local stress field is not consistent with the tectonic stress field before the Chi-chi mainshock;the Chi-chi mainshcok occurred after a few months when the local stress field is consistent with the tectonic stress field.Similarly,the compressive stress axis of the thrust fault type focal mechanism of Wenchuan mainshock coincides with the compressive stress axis of tectonic stress field inverted from the CMT solutions of earthquake occurred in the eastern part of Qinghai-Tibet Plateau,the local stress field inverted from the focal mechanisms of small and moderate earthquakes near Wenchuan mainshock is consistent with the tectonic stress field. When the local stress field is consistent with the thrust fault type stress field,the Wenchuan mainshock occurred immediately.With the stress accumulation near the source region,there are similar local stress field transformation phenomena before the thrust fault mainshock.When the local stress state transformed to the stress state of mainshock,the stress level is very high near the source region.It may be precursor of large earthquake and must arouse further concerns.
The 2008 Wenchuan earthquake and the 1999 Chi-Chi earthquake are both intraplate thrust fault earthquakes occurred under the tectonic setting of thrust-nappe.Through comparative analysis on CMT solutions,focal mechanism solutions of small and moderate earthquakes,and tectonic stress field near the mainshock region,we found that the thrust type focal mechanism of the Chi-Chi mainshock coincides with the tectonic stress field derived from the CMT solutions of earthquakes occurred in Taiwan central and western inland;but the small and moderate earthquakes randomly occurred near mainshock region resulted in strike slip type focal mechanisms,indicating the local stress field is not consistent with the tectonic stress field before the Chi-chi mainshock;the Chi-chi mainshcok occurred after a few months when the local stress field is consistent with the tectonic stress field.Similarly,the compressive stress axis of the thrust fault type focal mechanism of Wenchuan mainshock coincides with the compressive stress axis of tectonic stress field inverted from the CMT solutions of earthquake occurred in the eastern part of Qinghai-Tibet Plateau,the local stress field inverted from the focal mechanisms of small and moderate earthquakes near Wenchuan mainshock is consistent with the tectonic stress field. When the local stress field is consistent with the thrust fault type stress field,the Wenchuan mainshock occurred immediately.With the stress accumulation near the source region,there are similar local stress field transformation phenomena before the thrust fault mainshock.When the local stress state transformed to the stress state of mainshock,the stress level is very high near the source region.It may be precursor of large earthquake and must arouse further concerns.
引文
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[17] Shin Tzay-Chyn,Teng Ta-liang.An Overview of the 1999 Chi-Chi,Taiwan,Earthquake.Bulletin of the Seismological Society of America ,2001,91(5) :895～913
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[19] 张永久,程万正.用P、S波速度振幅比求小震机制解的可行性研究.中国地震,2007,23(4) :366～374 Zhang Y J ,Cheng W Z.Feasibility study on determining focal mechanism of small earthquakes using amplitude ratio of P and S waves.Earthquake Research in China (in Chinese),2007,23(4) :366～374
[20] Zobock M L.Zoback M D,Adams M,et al.Global patterns of tectonics stress.Nature,1989 ,341:291～298
[21] 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 Asia region.Acta Seismologica Sinica (in Chinese),2001,23 (5) :492～501
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Chen Y T ,Xu L S,Zhang Y ,et al.Report on the Wenchuan larger earthquake source of May 12,2008． (2008-05-25) http://www.csi.ae.cn/Sichuan
[23] 李延兴,张静华,周 伟等.汶川8． 0地震孕育发生的机制与动力学问题.地球物理学报,2009,52(2) :519～530 Li Y X,Zhang J H,Zhou W,et al.The mechanism and dynamics of the generation and occurrence for Wenchuan M_s8． 0 earthquake.Chinese J.Geophys.(in Chinese),2009,52(2) :519～530
[24] 郑秀芬,陈朝辉,张春贺.1 999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.地球物理学报,2008,51(1) :149～157 Zheng X F,Chen Z H,Zhang C H.Study on temporal variations of shear-wave splitting in the Chiayi area,aftershock zone of 1999 Chichi earthquake,Taiwan.Chinese J.Geophys.(in Chinese),2008 ,51(1) :149～157
[25] 周永胜,何昌荣.汶川地震区的流变结构与发震高角度逆断层滑动的力学条件.地球物理学报,2009,52(2) :474～484 Zhou Y S,He C R.The rheological structures of crust and mechanics of high-angle reverse fault slip for Wenchuan M_s8． 0 earthquake.Chinese].Geophys.(in Chinese),2009,52(2) :474～484
[2] Kao H,Chen W P.The Chi-Chi earthquake sequencef active out-of sequence thrust faulting in Taiwan.Science,2000,288:2346～2349
[3] Ma K F,Lee C T,Tsai Y B,et al.The Chi-Chi,Taiwan Earthquake:Large surface displacements on an inland thrust fault.EOS,1999,80 :605～611
[4] Xu X,Wen X,Yu G,et al.Coseismic reverse-and oblique-slip surface faulting generated by the 2008 M_w7． 9 Wenchuan earthquake,China.Geology,2009 ,37 :515～518
[5] 王卫民,赵连锋,李娟等.四川汶川8． 0级地震震源过程.地球物理学报,2008,51(5) :1403～1410 Wang W M,Zhao L F,Li J,et al.Rupture process of the M_s8． 0 Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.,2008,51 (5) :1403～1410
[6] 滕吉文,白登海,杨辉等.2008汶川M_s8． 0地震发生的深层过程和动力学响应.地球物理学报,2008,51(5) :1385～1402 Teng J W,Bai D H,Yang H,et al.Deep processes and dynamic responses associated with the Wenchuan M_s8． 0 earthquake of 2008． Chinese J.Geophys.,2008,51 (5) :1385～1402
[7] 刘启元,李 昱,陈九辉等.汶川M_s8． 0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2) :309～319 Liu Q Y,Li Y,Chen J H,et al.Wenchuan M_s8． 0 earthquake,preliminary study of the S-wave velocity structure of the crust and upper mantle.Chinese J.Geophys.,2009,52(2) :309～319
[8] Chen Wen-Shan,Huang Bor-Shouh,Chen Yue-Gau,et al.1999 Chi-Chi Earthquake:A case study on the role of thrust-ramp structures for generating earthquakes.Bull Seism Soci Amer,2001,91:986～994
[9] 晏锐.地震前兆观测资料分析//汶川8． 0级地震科学研究 报告.北京:地震出版社,2009:170～193 Yan R.Analysis on the observational data of earthquake precursory.In:The Monitoring and Forecasting Secretary of China Earthquake Administration,eds.The Scientific Research Report of Wenchuan M8． 0 Earthquake.Beijing:Seismological Press,2009． 170～193
[10] 罗兰格.我国地震综合预报方法研究的回顾与展望.华北地震科学,2002,20(4) :1～18 Luo L G.Review and prospection for the study on comprehensive prediction in China.North China Earthquake Science (in Chinese),2002,20(4) :1～18
[11] 张致伟,程万正,阮祥等.汶川8． 0级地震前龙门山断裂带的地震活动性和构造应力场特征.地震学报,2009,31(2) :117～127 Zhang Z W,Cheng W Z,Ruan X,et al.Seismicity and tectonic stress of the Longmenshan fault zone before 2008 Wenchuan M_s8． 0 earthquake.Acta Seismologica Sinica ,2009,31(2) :117～127
[12] 江准熙.1999年集集大地震前后地震活动、震源机制及地壳应力分布与变化之研究[博士论文].台湾“中央大学”地球物理研究所,2001 Jiang Z J.A study on the patterns and changes in seismicity,focal mechanism and crustal stress before and after the 1999 Chi-Chi,Taiwan,Earthquake [Ph.D.thesis].Taiwan:Institute of Geophysics,National Central University,2001
[13] 滕吉文,张永谦,闫雅芬.强烈地震震源破裂和深层过程与地震短临预测探索.地球物理学报,2009,52(2) :428～443 Teng J W,Zhang Y Q,Yan Y F.Deep process of the rupture of strong earthquakes and exploration for the impending earthquake prediction.Chinese J.Geophys.(in Chinese),2009,52(2) :428～443
[14] 许忠淮.用滑动矢量拟合法反演唐山余震区的平均应力场.地震学报,1985,7(4) :349～352 Xu Z H.Mean stress field in Tan gshan aftershock area obtained from focal mechanism data by fitting slip directions.Acta Seismologica Sinica(in Chinese) ,1985,7(4) :349～352
[15] 梁尚鸿,李幼铭,束沛镒等.利用区域地震台网P、S波振幅比资料测定小震震源参数.地球物理学报,1984,27(3) :247～257 Liang S H,Li Y M,Shu P Y,et al.On the determining of source parameters of small earthquakes by using amplitude ratios of P and S from regional network observations.Chinese J.Geophys.(in Chinese),1984 ,27(3) :247～257
[16] 许忠淮,戈澍谟.用滑动方向拟合法反演富蕴地震断裂带应力场.地震学报,1984,8(5) :395～404 Xu Z H.Ge S M.Stress field in the Fuyun,Xinjiang earthquake fracture zone determined by fitting fault slip vector dada.Acta Seismologica Sinica (in Chinese) ,1984 ,8(5) :395～404
[17] Shin Tzay-Chyn,Teng Ta-liang.An Overview of the 1999 Chi-Chi,Taiwan,Earthquake.Bulletin of the Seismological Society of America ,2001,91(5) :895～913
[18] 程万正,刁桂苓,吕弋培等.川滇地块的震源力学机制、运动速率和活动方式.地震地质,2003,25(1) :71～87 Cheng W Z,Diao G L,Lü Y P.Focal mechanisms,displacement rate and mode of motion of the Sichuan-Yunnan block.Seismology and Geology (in Chinese) ,2003,25(1) :71～87
[19] 张永久,程万正.用P、S波速度振幅比求小震机制解的可行性研究.中国地震,2007,23(4) :366～374 Zhang Y J ,Cheng W Z.Feasibility study on determining focal mechanism of small earthquakes using amplitude ratio of P and S waves.Earthquake Research in China (in Chinese),2007,23(4) :366～374
[20] Zobock M L.Zoback M D,Adams M,et al.Global patterns of tectonics stress.Nature,1989 ,341:291～298
[21] 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 Asia region.Acta Seismologica Sinica (in Chinese),2001,23 (5) :492～501
[22] 陈运泰,许力生,张 勇等.2008年5月12日汶川特大地震震源特性分析报告.(2008-05-25) http://www.csi.ac.cn/Sichuan
Chen Y T ,Xu L S,Zhang Y ,et al.Report on the Wenchuan larger earthquake source of May 12,2008． (2008-05-25) http://www.csi.ae.cn/Sichuan
[23] 李延兴,张静华,周 伟等.汶川8． 0地震孕育发生的机制与动力学问题.地球物理学报,2009,52(2) :519～530 Li Y X,Zhang J H,Zhou W,et al.The mechanism and dynamics of the generation and occurrence for Wenchuan M_s8． 0 earthquake.Chinese J.Geophys.(in Chinese),2009,52(2) :519～530
[24] 郑秀芬,陈朝辉,张春贺.1 999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.地球物理学报,2008,51(1) :149～157 Zheng X F,Chen Z H,Zhang C H.Study on temporal variations of shear-wave splitting in the Chiayi area,aftershock zone of 1999 Chichi earthquake,Taiwan.Chinese J.Geophys.(in Chinese),2008 ,51(1) :149～157
[25] 周永胜,何昌荣.汶川地震区的流变结构与发震高角度逆断层滑动的力学条件.地球物理学报,2009,52(2) :474～484 Zhou Y S,He C R.The rheological structures of crust and mechanics of high-angle reverse fault slip for Wenchuan M_s8． 0 earthquake.Chinese].Geophys.(in Chinese),2009,52(2) :474～484
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