2008年汶川大地震震源机制的时空变化
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摘要
本文提出了一种基于恒定破裂速度和固定子事件震源时间函数的假定、利用远场地震波形资料获取大地,震震源机制的时空变化图像的线性反演方法,并利用这种方法及个球范围内48个台站的长周期波形资料反演建立了2008年汶川M_S8.0地震的震源机制随时间和空间变化的图像.根据这个图像可知,汶川大地震断层的西南端震源机制接近于逆冲,随着破裂向东北方向延伸,震源机制的走滑分量逐渐增大,走滑分量超过逆冲分量的转折点在震中东北大约190 km的位置.为了检验反演方法的有效性和反演结果的可靠性,我们特别设计了一个数值试验对反演结果进行了检验.检验结果表明,我们在本文中提出的反演方法是有效的,关于汶川大地震的反演结果也是可靠的(除长周期信号较弱的一段外).通过比较发现,反演结果与震后野外考察的结果也相当吻合.
A linear inversion technique based on assumption of constant rupture velocity and fixed source time functions of sub-events is proposed in this paper for inverting teleseismic waveform data to image spatio-temporal variation of source mechanism of large earthquakes, and applied to the 2008 Wenchuan M_S8. 0 earthquake, obtaining its image of the spatio-temporal variation of source mechanism by inverting 48 worldwide stations of long period waveform data. The image shows that the mainly thrust mechanism appeared in the southwest segment of the fault, and the strike-slip component was getting more and more with the fault extending northeastwards, with the turning point at which the strike-slip component became larger than the thrust-slip component appearing around 190 km northeast to the epicenter. In order to inspect the validity of the used method and reliability of the inverted results a specially designed numerical test was performed. The inspection indicated that the inversion method proposed in this paper was valid and the inverted results regarding the great Wenchuan earthquake were trustable (except those on one segment where the long-period component is weak). A comparison shows that the inverted results were coincident with the field-investigation results.
A linear inversion technique based on assumption of constant rupture velocity and fixed source time functions of sub-events is proposed in this paper for inverting teleseismic waveform data to image spatio-temporal variation of source mechanism of large earthquakes, and applied to the 2008 Wenchuan M_S8. 0 earthquake, obtaining its image of the spatio-temporal variation of source mechanism by inverting 48 worldwide stations of long period waveform data. The image shows that the mainly thrust mechanism appeared in the southwest segment of the fault, and the strike-slip component was getting more and more with the fault extending northeastwards, with the turning point at which the strike-slip component became larger than the thrust-slip component appearing around 190 km northeast to the epicenter. In order to inspect the validity of the used method and reliability of the inverted results a specially designed numerical test was performed. The inspection indicated that the inversion method proposed in this paper was valid and the inverted results regarding the great Wenchuan earthquake were trustable (except those on one segment where the long-period component is weak). A comparison shows that the inverted results were coincident with the field-investigation results.
引文
[1] Lin A M, Kikuchi M, Fu B H. Rupture segmentation and process of the 2001 M_w 7． 8 central Kunlun, China, earthquake.Bull. Seis. Soc. Am. , 2003, 93:2477-2492
[2] Antolik M, Aberrcrombie R E, Ekstrom G. The 14 November 2001 Kokoxili (Kunlunshan) . Tibet, earthquake:rupture transfer through a large extensional step-Over, Bull. Seism. Soc. Am. , 2004, 94:1173-1194
[3] Tocheport A, Rivera L, Woerd J V. A study of the 14 November 2001 Kokoxili earthquake; history and geometry of the rupture from teleseismic data and field observations. Bull. Seis. Soc. Am. , 2006, 96:1729-1741
[4] 陈运泰,许力生,张勇等.汶川地震专题/地震情况/初步 研究及考察结果(一).http://www.cea-igp.ac.cn/pdf(2008-05-02) Chen Y T, Xu L S, Zhang Y, et al. Reports on the source characters of Wenchuan great earthquake occurred on 12~(th)May 2008． China seismic information network, 2008, http:// www. cea-igp. ac. cn/spccial_issue/earthquakesituation/preliminary_resulted),pdf (2008-05-02)
[5] 张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑:地球科学),2008,38(10) :1186-1194 Zhang Y, Feng W P, Xu L S, et al. Spatio-temporal rupture process of the 2008 great Wenchuan earthquake. Science China CSer D-Earth Sct), 2009, 52(2) :145-154
[6] 陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3) :657-673 Chen G G, Ji F j, Zhou R J, et al. Primary research of activity segmentation of Longmenshan fault zone since Late-Quaternary. Seismology and Geology (in Chinese),2007, 29(3) :657-673
[7] 徐锡伟,闻学泽,叶建青等.汶川M_s8． 0地震地表破裂带及其发震构造.地震地质,2008,30(3) :597-629 Xu X W, Wen X Z, Ye J Q, et al. The M_s8． 0 Wenchuan earthquake surface ruptures and its seismogenic structure. Seismology and Geology (in Chinese), 2008,30(3) :597-629
[8] 张勇.地震震源破裂过程反演方法研究[博士论文].北京:北京大学地球与空间科学学院,2008． 1-158 Zhang Y. Study on the inversion methods of source rupture process [Ph. D. dissertation] (in Chinese). Beijing:School of Earth and Space Science, Peking University, 2008． 1-158
[9] Kikuchi M, Kanamori H. Inversion of complex body waves-Ⅱ. Phys. Earth Planet. Interiors,1986, 43:205-222
[10] Kikuchi M, Kanamori H. Inversion of complex body waves -Ⅲ. Bull. Seism. Soc. Am. , 1991, 81:2335-2350
[11] ZahradniK J, Serpetsidaki A, Sokos E, et al. Iterative deconvolution of regional waveforms and a double-event interpretation of the 2003 Lefkada earthquake, Greece. Bull. Seism. Soc. Am. , 2005, 95:159-172
[12] Ekstrom G. A very broadband inversion method for the recovery of earthquake source parameters. Tectonophysics, 1989, 166:73-100
[13] Aki K, Richards P. Quantitative Seismology:Theory and Methods. Vols Ⅰ and Ⅱ. San Francisco:W H Freeman, 1980． 1-932
[14] Chen Y T, Xu L S. A time-domain inversion technique for the tempo-spatial distribution of slip on a finite fault plane with applications to recent large earthquakes in the Tibetan Plateau. Geophys. J. Int. , 2000, 143:407-416
[15] Xu L S, Chen Y T, Teng T L, Patau G. Temporal and spatial rupture process of the 1999 Chi-Chi earthquake from IRIS and GEOSCOPE long period waveform data using aftershocks as empirical Greens functions. Bull. Seism. Soc. Am. , 2002, 92:3210-3228
[16] Yagi Y, Kikuchi M. Source rupture process of the Kocaeli, Turkey, earthquake of August 17, 1999, obtained by joint inversion of near-field data and teleseismic data. Geophys. Res. Lett. , 2000, 27:1969-1972
[17] Ward S N? Barrientos S E. An inversion for slip distribution and fault shape from geodetic observations of the 1983, Borah Park, Idaho, earthquake. J. Geophys. Res., 1986, 91 (B5) : 4909-4919
[18] Liu C, Zhang Y, Xu L S, et al. A new technique for moment tensor inversion with applications to the 2008 Wenchuan M_s8． 0 earthquake sequence. Acta Seismologica Sinica, 2008, 21(4) :333-343
[19] Kennett B L N. Seismic Wave Propagation in Stratified Media. Cambridge:Cambridge University Press, 1983． 1-339
[20] Kennett B L N, Engdahl E R. Travel times for global earthquake location and phase identification. Geophys. J. Int. , 1991, 105: 429-465
[21] Hartzell S H, Heaton T H. Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake. Bull. Seism. Soc, Am. , 1983, 73:1553-1583
[22] 张勇,许力生,陈运泰.提取视震源时间函数的PLD方法及其对2005年克什米尔M_w7． 6地震的应用.地球物理学报,2009,待发表 Zhang Y, Xu L S, Chen Y T. PLD method for retrieving-apparent source time function and its application to 2005 Kashmir M_w7． 6 earthquake. Chinese J. Geophys. (in Chinese), 2009, In Press
[2] Antolik M, Aberrcrombie R E, Ekstrom G. The 14 November 2001 Kokoxili (Kunlunshan) . Tibet, earthquake:rupture transfer through a large extensional step-Over, Bull. Seism. Soc. Am. , 2004, 94:1173-1194
[3] Tocheport A, Rivera L, Woerd J V. A study of the 14 November 2001 Kokoxili earthquake; history and geometry of the rupture from teleseismic data and field observations. Bull. Seis. Soc. Am. , 2006, 96:1729-1741
[4] 陈运泰,许力生,张勇等.汶川地震专题/地震情况/初步 研究及考察结果(一).http://www.cea-igp.ac.cn/pdf(2008-05-02) Chen Y T, Xu L S, Zhang Y, et al. Reports on the source characters of Wenchuan great earthquake occurred on 12~(th)May 2008． China seismic information network, 2008, http:// www. cea-igp. ac. cn/spccial_issue/earthquakesituation/preliminary_resulted),pdf (2008-05-02)
[5] 张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑:地球科学),2008,38(10) :1186-1194 Zhang Y, Feng W P, Xu L S, et al. Spatio-temporal rupture process of the 2008 great Wenchuan earthquake. Science China CSer D-Earth Sct), 2009, 52(2) :145-154
[6] 陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3) :657-673 Chen G G, Ji F j, Zhou R J, et al. Primary research of activity segmentation of Longmenshan fault zone since Late-Quaternary. Seismology and Geology (in Chinese),2007, 29(3) :657-673
[7] 徐锡伟,闻学泽,叶建青等.汶川M_s8． 0地震地表破裂带及其发震构造.地震地质,2008,30(3) :597-629 Xu X W, Wen X Z, Ye J Q, et al. The M_s8． 0 Wenchuan earthquake surface ruptures and its seismogenic structure. Seismology and Geology (in Chinese), 2008,30(3) :597-629
[8] 张勇.地震震源破裂过程反演方法研究[博士论文].北京:北京大学地球与空间科学学院,2008． 1-158 Zhang Y. Study on the inversion methods of source rupture process [Ph. D. dissertation] (in Chinese). Beijing:School of Earth and Space Science, Peking University, 2008． 1-158
[9] Kikuchi M, Kanamori H. Inversion of complex body waves-Ⅱ. Phys. Earth Planet. Interiors,1986, 43:205-222
[10] Kikuchi M, Kanamori H. Inversion of complex body waves -Ⅲ. Bull. Seism. Soc. Am. , 1991, 81:2335-2350
[11] ZahradniK J, Serpetsidaki A, Sokos E, et al. Iterative deconvolution of regional waveforms and a double-event interpretation of the 2003 Lefkada earthquake, Greece. Bull. Seism. Soc. Am. , 2005, 95:159-172
[12] Ekstrom G. A very broadband inversion method for the recovery of earthquake source parameters. Tectonophysics, 1989, 166:73-100
[13] Aki K, Richards P. Quantitative Seismology:Theory and Methods. Vols Ⅰ and Ⅱ. San Francisco:W H Freeman, 1980． 1-932
[14] Chen Y T, Xu L S. A time-domain inversion technique for the tempo-spatial distribution of slip on a finite fault plane with applications to recent large earthquakes in the Tibetan Plateau. Geophys. J. Int. , 2000, 143:407-416
[15] Xu L S, Chen Y T, Teng T L, Patau G. Temporal and spatial rupture process of the 1999 Chi-Chi earthquake from IRIS and GEOSCOPE long period waveform data using aftershocks as empirical Greens functions. Bull. Seism. Soc. Am. , 2002, 92:3210-3228
[16] Yagi Y, Kikuchi M. Source rupture process of the Kocaeli, Turkey, earthquake of August 17, 1999, obtained by joint inversion of near-field data and teleseismic data. Geophys. Res. Lett. , 2000, 27:1969-1972
[17] Ward S N? Barrientos S E. An inversion for slip distribution and fault shape from geodetic observations of the 1983, Borah Park, Idaho, earthquake. J. Geophys. Res., 1986, 91 (B5) : 4909-4919
[18] Liu C, Zhang Y, Xu L S, et al. A new technique for moment tensor inversion with applications to the 2008 Wenchuan M_s8． 0 earthquake sequence. Acta Seismologica Sinica, 2008, 21(4) :333-343
[19] Kennett B L N. Seismic Wave Propagation in Stratified Media. Cambridge:Cambridge University Press, 1983． 1-339
[20] Kennett B L N, Engdahl E R. Travel times for global earthquake location and phase identification. Geophys. J. Int. , 1991, 105: 429-465
[21] Hartzell S H, Heaton T H. Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake. Bull. Seism. Soc, Am. , 1983, 73:1553-1583
[22] 张勇,许力生,陈运泰.提取视震源时间函数的PLD方法及其对2005年克什米尔M_w7． 6地震的应用.地球物理学报,2009,待发表 Zhang Y, Xu L S, Chen Y T. PLD method for retrieving-apparent source time function and its application to 2005 Kashmir M_w7． 6 earthquake. Chinese J. Geophys. (in Chinese), 2009, In Press
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