盈江中强地震序列震源机制及区域地壳流变特征和断层性质研究
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摘要
2008年云南西部盈江地区连续发生了4次中强地震,本文运用全波形模拟的方法研究了这4次中强地震序列的震源机制解.并对4次地震序列进行了重定位.我们结合由震源机制解得到的主应力轴倾角变化情况,震源深度和重定位深度对盈江地区地壳流变特征进行了分析.分析认为盈江地区下地壳内的岩石并不是完全塑性的,而是具有一定的强度从而可以发生脆性破裂.同时,我们还根据震源机制解对这4次中强地震序列的发震断裂,北东走向的大盈江断裂和南北走向的苏典断裂的断层性质进行了初步分析.分析结果认为大盈江断裂是一主要切割上地壳的左旋走滑断裂.南北走向的苏典断裂是一右旋断裂,其北端切割地壳深度较南端浅.苏典断裂的南端切割地壳深度达到下地壳,且上地壳部分的断裂断层面较陡直,而下地壳中的断裂的断层面比较平缓.盈江位于云南西部的中缅交界地区,目前对这一区域活动断裂的研究较少.本文给出的盈江地区两条活动断裂的初步研究结果,将给关于青藏高原的研究提供来自于喜马拉雅东触角附近断层的信息.
Four mid-size earthquakes stroke the Yingjiang county in western Yunnan in 2008.We apply the full waveform modeling method to study the focal mechanisms of four earthquake sequences.We also relocate four earthquake sequences.Based on the variation of plunge angle of principal stresses,focal mechanisms,and relocation results we analyse the regional rheology in the crust.Our results suggest that the lower crust in Yingjiang region is brittle instead of completely plastic because we observed seven events in the lower crust from the waveform modeling.We also study the properties of two seismogenic faults,northeast trending Dayingjiang fault and northsouth striking Sudian fault,based on the dip angle and focal depth.The results suggest that Dayingjiang fault is a left-lateral strike slip fault cutting upper crust,and northsouth trending Sudian fault is a right-lateral fault whose south tip cutting crust deeper than its north tip.South tip of Sudian fault reaches lower crust,its fault plane in the upper crust is dip and its fault plane in the lower crust is relatively gental.
Four mid-size earthquakes stroke the Yingjiang county in western Yunnan in 2008.We apply the full waveform modeling method to study the focal mechanisms of four earthquake sequences.We also relocate four earthquake sequences.Based on the variation of plunge angle of principal stresses,focal mechanisms,and relocation results we analyse the regional rheology in the crust.Our results suggest that the lower crust in Yingjiang region is brittle instead of completely plastic because we observed seven events in the lower crust from the waveform modeling.We also study the properties of two seismogenic faults,northeast trending Dayingjiang fault and northsouth striking Sudian fault,based on the dip angle and focal depth.The results suggest that Dayingjiang fault is a left-lateral strike slip fault cutting upper crust,and northsouth trending Sudian fault is a right-lateral fault whose south tip cutting crust deeper than its north tip.South tip of Sudian fault reaches lower crust,its fault plane in the upper crust is dip and its fault plane in the lower crust is relatively gental.
引文
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[2]Stock J M,Molnar P.Revised history of the early Tertiaryplate motion in the southwest Pacific.Nature,1987,325,495-499.
[3]Tapponnier P,Peltzer G,Le Dain AY,et al.Propagatingextrusion tectonics in Asia:new insights from simpleexperiments with plasticine.Geology,1982,10,611-616.
[4]Royden L.Coupling and decoupling of crust and mantle inconvergent orogens:implications fro strain partitioning in thecrust.J.Geophys.Res.1996,101,17679-17705.
[5]Guzman-Speziale M,Ni J F.Seismicity and active tectonics ofthe western Sudan Arc.The Tectonic Evolution of Asia,Cambridge Univ.Press.1996,63-84.
[6]Royden L H,Burchfiel B C,van der Hilst R D.The geologicalevolution of the Tibetan Plateau.Science.2008,321,1054-1058.
[7]Maurin T F,Masson C,Rangin U T,et al.First globalpostioning system results in northern Myanmar:constant andlocalized slip rate along the Sagaing fault.Geological Society ofAmerica,2010,38,591-594.
[8]Pivnik D,Nahm J,Tucker R,et al.Polyphase deformation ina fore-arc/back-arc basin,Salin Basin,Burma.AmericanAssociation of Petroleum Geologists Bulletin,2008,82,1054-1058.
[9]Waldhauser F,Ellsworth W L.A double-difference earthquakelocation algorithm:method and application to the NorthernHayward fault,California,Bull.Seismol.Soc.Am.,2000,90,1353-1368.
[10]Xu Y,Herrmann R B,Koper K D.Source parameters ofregional small-to-moderate earthquakes in the Yunnan-Sichuan region of China.Bull.Seismol.Soc.Am.,2010,100,2518-2531.
[11]Herrmann R B,Malagnini L,Munafo I.Regional momenttensors of the 2009 L'Aquila earthquake sequence.Bull.Seismol.Soc.Am.,2011,101.
[12]Hardebeck JL,Shearer P M.A new method for determiningfirst-motion focal mechanism,Bull.Seism.Soc.Am.,2002,92,2264-2276.
[13]Oppenheimer D H,Reasenberg P A,Simpson R W.Faultplane solutions for the 1984 Norgan Hill,California,earthquake sequence:evidence for the state of stress on theCalaveras fault,J.Geophys.Res.,1988,93,9007-9026.
[14]Kilb D,Hardebeck J L.Fault parameter constraints usingrelocated earthquakes:a validation of first-motion focalmechanism data.Bull Seism Soc Am,2006,96,1140-1158.
[15]Zhao L S,Helmberger D V.Source estimation from broadbandregional seismograms,Bull.Seism.Soc.Am.1994,84,91-104.
[16]Zhu L,Helmberger D V.Advancement in source estimationtechniques using broadband regional seismograms,Bull.Seism.Soc.Am.1996,86,1634-1641.
[17]Xu L,Rodenay S,van der Hilst R D.Structure of the crustbeneath the sourtheastern Tibetan Plateau from teleseismicreceiver functions.Phys.Earth Planet Int.,2007,165,176-193.
[18]石耀霖,朱守彪.中国大陆震源机制深度变化反映的地壳-地幔流变特征.地球物理学报,2003,46,359-365.SHi Yaolin.Contrast of rheology in the crust and mantle nearmoho revealed by depth variation of earthquake mechanism incontinental China.Chinese J.Geophys.(in Chinese),2003,46(3):359-365.
[19]Xu Z J,Song X.Joint inversion for crustal and Pn velocitiesand Moho depth in eastern margin of the Tibetan plateau.Tectonophysics,2010,491,185-193.
[20]高星,郭志,王卫民等.用转换函数方法研究腾冲-临沧地区地壳结构.地球物理学报,2008,51,451-459.GAO Xing;GUO Zhi;WANG Wei-Min;YAO Zhen-Xing.Crust structure beneath Tengchong-Lincang region,Yunnanprovince,revealed by transform function.Chinese J.Geophys.(in Chinese),2008,51(2):451-459.
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