汶川地震余震区东北端一个余震序列的地震学研究
摘要
以往研究结果表明,大陆板内成熟断层的浅部有断层泥的充填,不能积累足够应变产生地震,所以绝大多数地震的深度都深于5km.而年轻断层或完整岩体在积累足够应变的情况下可以发生浅于3km的地震.汶川地震形成了200多公里的地表破裂,但是远震波形反演及余震分布表明,主震可能继续往北东方向的地下破裂了50多公里,在破裂区东北端深部破裂可能引起浅部应力增加,从而产生浅震.2008年7月24日在汶川地震破裂带东北端青川发生了一次Ms5.7级的余震.CAP方法反演表明,此次地震的震源机制解为逆冲型,深度为3km.为了进一步确认震源深度,本文利用震中距约15km的近台L0205观测到的深度震相sPL及面波体波振幅比确认其深度.由于地震深度小于震中距1/5,Rayleigh波才能发育,在15km左右的距离上观测到远强于SV波的Rg波,这也充分证明了这次地震的震源很浅.在该台上还观测到该地震序列多次余震的sPL,由此得到的震源深度都浅于3km.另一方面,由于实地考察和InSAR研究没有发现汶川主震在这个地区有地表破裂,所以本文认为这个地震序列是由于深部破裂引起浅部应力增加而导致完整岩体的新鲜破裂,而非沿着汶川主震破裂带发生.研究余震深度变化趋势及发震断层对认识主震发震机理及理解破裂带特征具有重要意义.
引文
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25Uski M,Hyvonen T,Korja A,et al.Focal mechanisms of three earthquakes in Finland and their relation to surface faults.Tectonophysics,2003,363:141—157
26Chen S F,Wilson C J L,Deng Q D,et al.Active faulting and block movement associated with large earthquakes in the Min Shan and Longmen Mountains,northeastern Tibetan Plateau.J Geophys Res,1994,99:20024—24038
27马保起,苏刚,侯治华,等.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率.地震地质,2005,27:234—242
28杨晓平.龙门山断裂带南段错断晚更新世以来地层的证据.地震地质,1999,21:341—345
29张培震,徐锡伟,闻学泽,等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51:1066—1073.
30Burchfield B C,Royden L H,Hilst R D,et al.Geological and geophysical context for the Wenchuan Earthquake of12May2008,Sichuan,People’s Republic of China.GSA Today,2008,18:4—14
31孙建宝,梁芳,沈正康,等.汶川Ms8.0地震InSAR形变观测及初步分析.地震地质,2008,30:789—795
32徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造.地震地质,2008,30:597—629
33赵珠,范军,郑斯华.龙门山断裂带地壳速度结构和震源位置的精确修定.地震学报,1997,19:615—622
34王椿镛,韩渭宾,吴建平,等.松潘-甘孜造山带地壳速度结构.地震学报,2003,25:229—241
35Kobayashi T,Takada Y,Furuya M,et al.Locations and types of ruptures involved in the2008Sichuan.Geophys Res Lett,2009,36:L07302
36Lay T,Wallace T.Modern Global Seismology.San Diego:Academic Press,1995.1—521
37Crampin 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
38陈颙.震源机制一致性作为描述地震活动性的新参数.地球物理学报,1978,21:140—159
2马宗晋,张家声,刘国栋.大陆多震层研究现状和讨论.地震地质,1990,12:262—264
3丁志锋,曾融生.京津唐地区震源深度分布初探.地震学报,1990,12:242—247
4张国民,汪素云,李丽.中国大陆地震震源深度及其构造含义.科学通报,2002,47:663—668
5黄媛,吴建平,张天中,等.汶川8.0级大地震及其余震序列重定位研究.中国科学D辑,2008,38:1242—1249
6朱艾斓,徐锡伟,刁桂苓,等.汶川Ms8.0地震部分余震重新定位及地震构造初步分析.地震地质,2008,30:759—767
7郑勇,马宏生,吕坚,等.汶川地震强余震(Ms≥5.6)的震源机制解及其与发震构造的关系.中国科学D辑,2009,39:1—14
8张瑞青,吴庆举,李永华,等.汶川中强余震震源深度的确定及其意义.中国科学D辑,2008,38:1234—1241
9陈九辉,刘启元,李顺成.汶川Ms8.0地震余震序列重新定位及其地震构造研究.地球物理学报.2009,52:390—397
10吴建平,黄媛,张天中,等.汶川Ms8.0震分布及周边区域P波三维速度结构研究.地球物理学报,2009,52:320—328
11Langston C A.Depth of faulting during the1968Meckering Australia earthquake sequence determined from waveform analysis of local seismograms.J Geophys Res,1987,92:561—574
12Ma S,Atkinso M G.Focal depths for small to moderate earthquakes(Mn≥2.8)in western quebec southern Ontario and northern New York.Bull Seis Soc Amer,2006,96:609—623
13Kim Y W,Dineva S,Ma S,et al.The4August2004,Lake Ontario Earthquake.Seis Res Lett,2006,77:65—73
14Engdahl E R,Hilst R V D,Buland R.Global teleseismic earthquake relocation with improved travel times and procedures for depth determination.Bull Seis Soc Amer,1998,88:722—743
15Murphy J R,Barker B W.Improved focal-depth determination through automated identification of the seismic depth phases pP and sP.Bull Seis Soc Amer,2006,96:1213—1229
16高立新,刘芳,赵蒙生,等.用sPn震相计算震源深度的初步分析与应用.西北地震学报,2007,29:213—244
17房明山,杜安陆,董孝平,等.用sPn震相测定近震震源深度.地震地磁观测与研究,1995,16:13—18
18任克新,邹立晔,刘瑞丰,等.用sPn计算内蒙地震的震源深度.地震地磁观测与研究.2004,25:24—31
19Bock G,Grunthal G,Wylegalla K.The1985/86Western Bohemia earthquakes:Modeling source parameters with synthetic seismograms.Tectonophysics,1996,261:139—146
20Zhao L S,Helmberger D V.Source estimation from broadband regional seismograms.Bull Seis Soc Amer,1994,84:91—104
21Zhu L P,Helmberger D V.Advancement in source estimation techniques using broadband regional seismograms.Bull Seis Soc Amer,1996,86:1634—1641
22Saikia C K.A method for path calibration using regional and teleseismic broadband seismograms:Application to the21May1997Jabalpur,India earthquake(Mw5.8).Curr Sci,2000,79:1301—1311
23Saikia C K,Woods B B and Thio H k.Calibration of the regional crustal waveguide and the retrieval of source parameters using waveform modeling.Pure Appl Geophys,2001,158:1301—1338
24Bent A L,Perry H K C.Depths of eastern Canadian earthquakes from regional data.Seism Res Lett,2002,73:273—284
25Uski M,Hyvonen T,Korja A,et al.Focal mechanisms of three earthquakes in Finland and their relation to surface faults.Tectonophysics,2003,363:141—157
26Chen S F,Wilson C J L,Deng Q D,et al.Active faulting and block movement associated with large earthquakes in the Min Shan and Longmen Mountains,northeastern Tibetan Plateau.J Geophys Res,1994,99:20024—24038
27马保起,苏刚,侯治华,等.利用岷江阶地的变形估算龙门山断裂带中段晚第四纪滑动速率.地震地质,2005,27:234—242
28杨晓平.龙门山断裂带南段错断晚更新世以来地层的证据.地震地质,1999,21:341—345
29张培震,徐锡伟,闻学泽,等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51:1066—1073.
30Burchfield B C,Royden L H,Hilst R D,et al.Geological and geophysical context for the Wenchuan Earthquake of12May2008,Sichuan,People’s Republic of China.GSA Today,2008,18:4—14
31孙建宝,梁芳,沈正康,等.汶川Ms8.0地震InSAR形变观测及初步分析.地震地质,2008,30:789—795
32徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造.地震地质,2008,30:597—629
33赵珠,范军,郑斯华.龙门山断裂带地壳速度结构和震源位置的精确修定.地震学报,1997,19:615—622
34王椿镛,韩渭宾,吴建平,等.松潘-甘孜造山带地壳速度结构.地震学报,2003,25:229—241
35Kobayashi T,Takada Y,Furuya M,et al.Locations and types of ruptures involved in the2008Sichuan.Geophys Res Lett,2009,36:L07302
36Lay T,Wallace T.Modern Global Seismology.San Diego:Academic Press,1995.1—521
37Crampin 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
38陈颙.震源机制一致性作为描述地震活动性的新参数.地球物理学报,1978,21:140—159
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