青藏高原东缘下地壳流动的地震学证据
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摘要
在2000年完成的穿过川西高原和四川盆地的深地震测深剖面揭示了川西高原的地壳结构具有地壳增厚(主要是下地壳增厚)、地壳平均速度低等特点,显示地壳的缩短与增厚的碰撞变形特征。根据川西高原上设置各爆炸点的记录截面图共同呈现PmP(莫霍界面反射波)弱能量的特点,推断在川西高原的下地壳介质具有强衰减(Qp=100~300)的性质。利用我国西部地区的宽频带地震台站的面波资料反演青藏高原及其邻区的地壳上地幔S波三维速度结构,在周期T=29.2s和T=42.9s的Rayleigh波群速度分布图上,显示了青藏高原东部(包括川西高原)呈现大范围的低速异常。多方面的结果表明,地震学方法为当前流行的下地壳流动模型提供了深部证据。
The seismic sounding profile through the crust of both West Sichuan Plateau and Sichuan Basin carried out in 2000 shows that the crust structure of the west Sichuan Plateau is of following characters:the low crust incrassating,low average velocity,the crust shortening and incrassating.According to the seismic profiles recorded in the West Sichuan Plateau,we conclude that the energy of PmP(the reflective wave of the Moho Discontinuity)is weak and the low crust is of strong attenuation character(Op=100～300).Using the surface wave data recorded with the broadband seismometers located in the west part of China,we make inversion calculation on the S wave 3-Dimension velocity structure of upper mantle.And our calculation results show that with the distribution figures of the Rayleigh wave group,(periods T=29.2s and T=42.9s),there are large abnormal areas with the low velocities around the east part of Qinghai-Tibet Plateau(including the west Sichuan Plateau).From other researching aspects,the seismological method provides the evidences to support the flowing model of low mantle,which are popular in the researchers.
The seismic sounding profile through the crust of both West Sichuan Plateau and Sichuan Basin carried out in 2000 shows that the crust structure of the west Sichuan Plateau is of following characters:the low crust incrassating,low average velocity,the crust shortening and incrassating.According to the seismic profiles recorded in the West Sichuan Plateau,we conclude that the energy of PmP(the reflective wave of the Moho Discontinuity)is weak and the low crust is of strong attenuation character(Op=100～300).Using the surface wave data recorded with the broadband seismometers located in the west part of China,we make inversion calculation on the S wave 3-Dimension velocity structure of upper mantle.And our calculation results show that with the distribution figures of the Rayleigh wave group,(periods T=29.2s and T=42.9s),there are large abnormal areas with the low velocities around the east part of Qinghai-Tibet Plateau(including the west Sichuan Plateau).From other researching aspects,the seismological method provides the evidences to support the flowing model of low mantle,which are popular in the researchers.
引文
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[8]Hwang,L.,and Mooney,W.D.,1986,Velocity and Q structure of the Great Valley,California,based on synthetic seismogramsmodeling of seismic refraction data,Bull.Seism.Soc.Am.,1986,76:1053-1067.
[9]Wang,C.-Y.,Lou,H.,Wu,J.P.,and Chen,W.,2006,Crustal structure beneath the eastern margin of the Tibetanplateau and its tectonic implications,J.Geophys.Res.(in press).
[10]苏伟,彭艳菊,郑月军,黄忠贤.青藏高原及其邻区地壳上地幔波速度结构[J].地球学报,2002,(23):193-200.
[2]Molnar,P.,and Deng Q.,1984,Faulting associated with large earthquakes and the average rate of deformation in central andeastern Asia,J.Geophys.Res.,89:6203-6227.
[3]Chen,S.F.,Wilson,C.J.L.,DENG,Q.D.,et al.,1994,Active faulting and block movement associated with largeearthquakes in the Min Shan and Longmen mountains,northeastern Tibetan plateau,J.Geophys.Res.,99:24025-24038.
[4]Chen,Z.,Burchfiel,B.C.,Liu,Y.,King,R.W.,Royden,L.H.,Tang,W.,Wang,E.,Zhao,J.,and Zhang,X.,2000,Global positioning system measurements from eastern Tibet and their implications for India/Eurasia intercontinentaldeformation,J.Geophys.Res.,105,16,215-16,227,2000.
[5]Royden,L.H.,Burchfiel,B.C.,King,R.W.,Wang,E.,Chen,Z.,Shen,F.,and Liu,Y.,1997,Surface deformationand lower crustal flow in eastern Tibet,Science,276:788-790.
[6]Fuchs,K.,and Mueller,G.,1971,Computation of synthetic seismograms with the reflectivity method and comparison with theobservations,Geophys.J.R.astr.Soc.,23:417-433.
[7]Sandmeier,K.J.,and Wenzel,F.,1986,Synthetic seismograms for a complex crustal model.Geophys.Res.Lett.,13:22-25.
[8]Hwang,L.,and Mooney,W.D.,1986,Velocity and Q structure of the Great Valley,California,based on synthetic seismogramsmodeling of seismic refraction data,Bull.Seism.Soc.Am.,1986,76:1053-1067.
[9]Wang,C.-Y.,Lou,H.,Wu,J.P.,and Chen,W.,2006,Crustal structure beneath the eastern margin of the Tibetanplateau and its tectonic implications,J.Geophys.Res.(in press).
[10]苏伟,彭艳菊,郑月军,黄忠贤.青藏高原及其邻区地壳上地幔波速度结构[J].地球学报,2002,(23):193-200.
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