由地震简正模式观测得到的内核各向异性区域变化
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摘要
地球的固体内核被对流的液体外核包围,由此创建了驱动地球磁场的地核发电机。用压缩体波研究地震显示出内核各向异性结构的半球性变化,但由于受地震和接收器分布状况所限,这一结论还不够充分。本文中,利用大地震的简正模式分裂函数测定结果,并基于扩展交叉耦合理论,我们观测到了区域变化和内核中东、西两半球的各向异性。这一模式与地球磁场的相似性说明在固化或组构演变过程中由Maxwell应力引起的晶体排列的凝入是产生各向异性的根源。这些观测结果限制了内核超速旋转的总量,但与振荡相符。
引文
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[2]Gubbins D,Alfe D,Masters G,et al.Can the Earth′s dynamo run on heat alone?Geophys.J.Int.,2003,155:609-622
[3]Morelli A,Dziewonski A M,Woodhouse J H.Anisotropy of the inner core inferred from PKIKP travel times.Geophys.Res.Lett.,1986,13:1545-1548
[4]Woodhouse J H,Giardini D,Li X-D.Evidence for inner core anisotropy from free oscillations.Geophys.Res.Lett.,1986,13:1549-1552
[5]Song X-D,Richards P G.Seismological evidence for differential rotation of the Earth′s inner core.Na-ture,1996,382:221-224
[6]Tanaka S,Hamaguchi H.Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC)-PKP(DF)times.J.Geophys.Res.,1997,102(B2):2925-2938
[7]Aubert J,Amit H,Hulot G,et al.Thermochemical flows couple the Earth′s inner core growth to man-tle heterogeneity.Nature,2008,454:758-761
[8]Niu F,Wen L.Hemispherical variations in seismic velocity at the top of the Earth′s inner core.Nature,2001,410:1081-1084
[9]Giardini D,Li X-D,Woodhouse J H.Splitting functions of long-period normal modes of the Earth.J.Geophys.Res.,1988,93(B11):13716-13742
[10]Beghein C,Trampert J.Robust normal mode constraints on inner-core anisotropy from model space search.Science,2003,299:552-555
[11]Ishii M,Tromp J,Dziewonski A M,et al.Joint inversion of normal mode and body wave data for inner core anisotropy1.Laterally homogeneous anisotropy.J.Geophys.Res.,2002,107(B12):2379-2395
[12]Durek J J,Romanowicz B.Inner core anisotropy inferred by direct inversion of normal mode spectra.Geophys.J.Int.,1999,139:599-622
[13]Deuss A,Woodhouse J H.Theoretical free-oscillation spectra:The importance of wide band coupling.Geophys.J.Int.,2001,146:833-842
[14]Irving J C E,Deuss A,Woodhouse J H.Normal mode coupling due to hemispherical anisotropic struc-ture in Earth′s inner core.Geophys.J.Int.,2009,178:962-975
[15]Resovsky J S,Ritzwoller M H.New and refined constraints on three-dimensional Earth structure from normal modes below3mHz.J.Geophys.Res.,1998,103(B1):783-810
[16]He X,Tromp J.Normal-mode constraints on the structure of the Earth.J.Geophys.Res.,1996,101(B9):20053-20082
[17]Romanowicz B,Breger L.Anomalous splitting of free oscillations:A reevaluation of possible interpreta-tions.J.Geophys.Res.,2000,105(B9):21559-21578
[18]Ritsema J,van Heijst H J.Woodhouse.Complex shear wave velocity structure imaged beneath Africa and Iceland.Science,1999,286:1925-1928
[19]Yu W,Wen L.Complex seismic anisotropy in the top of the Earth′s inner core beneath Africa.J.Geo-phys.Res.,2007,112:B08304,doi:10.1029/2006JB004868
[20]Bergman M I.Measurements of elastic anisotropy due to solidification texturing and the implications of the Earth′s inner core.Nature,1997,389:60-63
[21]Jeanloz R,Wenk H R.Convection and anisotropy of the inner core.Geophys.Res.Lett.,1988,15:72-75
[22]Yoshida S I,Sumita I,Kumazawa M.Growth model of the inner core coupled with the outer core dy-namics and the resulting elastic anisotropy.J.Geophys.Res.,1996,101(B12):28085-28103
[23]Karato S.Seismic anisotropy of the Earth′s inner core resulting from flow induced by Maxwell stresses.Nature,1999,402:871-873
[24]Buffett B A,Wenk H-R.Texturing of the Earth′s inner core by Maxwell stresses.Nature,2001,413:60-63
[25]Kelly P,Gubbins D.The geomagnetic field over the past5million years.Geophys.J.Int.,1997,128:315-330
[26]Johnson C L,Constable C G.The time-averaged geomagnetic field as recorded by lava flows over the past5Myr.Geophys.J.Int.,1995,122:489-519
[27]Jackson A,Jonkers A R T,Walker M R.Four centuries of geomagnetic secular variation from historical records.Philos.Trans.R.Soc.Lond.A,2000,358:957-990
[28]Bloxham J,Gubbins D.Thermal core-mantle interactions.Nature,1987,325:511-513
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