西太平洋下D”区的剪切波各向异性
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摘要
利用来自汤加—斐济及周边地区发生的47次地震并由中国地震台网中心和IRIS台站记录到的数据,与来自东亚北部及北太平洋地区发生的26次地震并由IRIS台站记录到的数据,使用ScS-S相对走时分析方法研究了西太平洋下D"区的剪切波各向异性,得到了核幔边界反射点上ScS波径向分量和横向分量的分裂时间,并计算了D"区的地震波各向异性强度.发现ScS波通过西太平洋下D"区时普遍呈现出径向分量走时大于横向分量走时的模式.ScS波的分裂时间值为-0.91~3.21s,平均值为1.1s;各向异性强度值为-0.45%~1.56%,平均值为0.52%.观测和分析结果表明,西太平洋下D"区水平流应占支配地位,各向异性结构主要是具有垂直对称轴的横向各向同性介质.形成这种结构的可能原因是地幔底部水平流导致的核幔边界反应产物或部分熔融物质的形状优选方向,或下地幔物质的晶格优选方向.
Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS,and from 26 northeast Asia and north Pacific events recorded by IRIS,we studied the shear wave anisotropy in D" region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary(CMB)reflection point.We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D" region.The splitting time values of ScS wave range from-0.91 s to 3.21 s with an average value of 1.1 s.The strength of anisotropy varies from-0.45% to 1.56% with an average value of 0.52%.The observations and analyses show that in the D" region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure.This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.
引文
高原,滕吉文.2005.中国大陆地壳与上地幔地震各向异性研究[J].地球物理学进展,20(1):180-185.
    刘堃,张中杰,胡家富,等.2001.中国陆区S波分裂与上地幔各向异性[J].地球物理学进展,16(2):81-87.
    刘希强,周蕙兰,李红,等.2001.中国大陆及邻区上地幔各向异性研究[J].地震学报,23(4):337-348.
    罗艳,黄忠贤,彭艳菊,等.2004.中国大陆及邻区SKS波分裂研究[J].地球物理学报,47(5):812-821.
    滕吉文,张中杰,王光杰,等.2000.地球内部各圈层介质的地震各向异性与地球动力学[J].地球物理学进展,15(1):1-35
    王良书,陈运平,米宁,等.2005.从地震波各向异性到各向异性地震学:地震波各向异性研究综述[J].高校地质学报,11(4):544-554.
    王霄翔.2006.西太平洋下方地幔底部剪切波分裂研究[D]:[学位论文].合肥:中国科学技术大学地球与空间科学学院:104.
    姚陈,王培德,陈运泰.1992.卢龙地区S波偏振与上地壳裂隙各向异性[J].地球物理学报,35(3):305-315.
    郑斯华,高原.1994.中国大陆岩石层的方位各向异性[J].地震学报,16(2):131-140.
    Fouch MJ,Fischer K M,Wysession ME.2001.Lowermost mantle anisotropy beneath the Pacific:Imaging the sourceof the Hawaiian plume[J].Earth Planet Sci Lett,190:167-180.
    Garnero E J.2000.Lower mantle heterogeneity[J].Ann Rev Earth Planet Sci,28:509-537.
    Garnero E J.2004.Anew paradigmfor Earth′s core-mantle boundary[J].Science,304:834-836.
    Garnero E J,Maupin V,Lay T,et al.2004.Variable azimuthal anisotropy in Earth′s lowermost mantle[J].Science,306:259-261.
    Grand S P.2002.Mantle shear-wave tomography andthe fate of subducted slabs[J].Phil Trans Roy Soc Lond,A,360:2475-2491.
    He Y,Wen L,Zheng T.2006.Geographic boundary and shear wave velocity structure of the“Pacific anomaly”near thecore-mantle boundary beneath western Pacific[J].Earth Planet Sci Lett,244:302-314.
    Karato S.1998.Some remarks on the origin of seismic anisotropy in the D”layer[J].Earth Planets Space,50:1019-1028.
    Kendall J M,Silver P G.1998.Investigating causes ofD”anisotropy[C]∥The Core-Mantle Boundary Region,GeodynSer.Washington D C:AGU,28:97-118.
    Kennett B L N,Engdahl E R.1991.Traveltimes for global earthquake location and phase identification[J].Geophys JInt,105:429-465.
    Lay T,Williams Q,Garnero E J.1998.The core-mantle boundary layer and deep Earth dynamics[J].Nature,392:461-468.
    Lay T,Garnero EJ,Williams Q.2004.Partial meltingin a thermochemical boundarylayer at the base of the mantle[J].Phys Earth Planet Interi,146:441-467.
    Lay T,Hernlund J,Garnero E J,et al.2006.A Post-Perovskite Lens andD”heat flux beneath the Central Pacific[J].Science,314:1272-1276.
    Moore M M,Garnero E J,Lay T,et al.2004.Shear wave splitting and waveform complexity for lowermost mantlestructures withlow-velocity lamellae and transverse isotropy[J].J Geophys Res,109(B02319):doi:10.1029/2003JB002546.
    Oganov A R,Martonak R,Laio A,et al.2005.Anisotropy of Earth′sD”layer and stacking faults in the MgSi O3post-perovskite phase[J].Nature,438:1142-1144.
    Russell S A,Lay T,Garenero E.1999.Small-scalelateral shear velocity and anisotropy heterogeneity near the core-man-tle boundary beneaththe central Pacificimaged using broadband ScS waves[J].J Geophys Res,104:13183-13199.
    Stixrude L.1998.Elastic constants and anisotropy of MgSi O3perovskite,periclase,and Si O2at high pressure[C]∥TheCore-Mantle Boundary Region,Geodyn Ser.Washington D C:AGU,28:83-96.
    Wookey J,Stackhouse J S,Kendall J M,et al.2005.Efficacy of the post-perovskite phase as an explanation for lower-most-mantle seismic properties[J].Nature,438:1004-1007.
    Zhao D.2001.Seismic structure and origin of hotspots and mantle plumes[J].Earth Planet Sci Lett,192:251-265.

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