外核顶部刚性薄层探测
摘要
核幔边界作为固态地幔和液态外核的分界面,是地球深部最重要的间断面,界面两侧地震波速度和密度存在显著差异.研究表明,该界面上部的D"层存在较强的不均匀性和各向异性.研究人员利用地震学的方法,发现在某些区域D"层下部存在超低速区;近年来更有某些学者提出外核顶部某些区域可能存在一个刚性(固体)薄层,其剪切波速度约为1km/s,并认为形成该层的物理机制是在外核冷却过程中,物质分异产生轻元素聚集在外核顶部从而发生固结.分析了斐济-汤加地区深地震在美国4个主要台网(USarray,BK,US,CI)上记录到的PKKPbc波形,发现存在前驱波,从而证明非洲下部外核顶部可能存在核刚性层.通过波形拟合确定了该核刚性层的厚度约为1km.非洲下部核刚性层与前人利用P4KP和ScP波形在其他区域得到的刚性层模型较为一致.核刚性层的存在可能对核幔间的物质、能量、角动量耦合起到重要的影响.
引文
1朱介寿.下地幔及核幔边界结构及地球动力学.地球科学进展,2000,15(2):139-142
2侯渭,谢鸿森.关于地核和核幔边界区物质的成分及运动特征的研究进展.地球科学进展,1996,11(2):204-208
3唐群署,李丽红.核幔边界D区的地震学研究进展.地学前缘,2006,13(2):213-224
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5Rost S,Revenaugh J S.Detection of a D discontinuity in the south Atlantic using PKKP.Geophys Res Lett,2003,30(16):1840
6Rost S,Revenaugh J S.Small scale changes of core mantle boundary reflectivity studied using core reflected PcP.Phys Earth Planet Inter,2004,145:19-36
7Garnero E J,Helmberger D V.Further structural constraints and uncertainties of a thin laterally varying ultra low velocity layer at the base of the mantle.J Geophys Res,1998,103:12495-12509
8Garnero E J,Grand S P,Helmberger D V.Low P-wave velocity at the base of the mantle.Geophys Res Lett,1993,20:1843-1846
9Rost S,Revenaugh J S.Lateral variation of the small scale structure at the CMB west of Tonga-Fiji.AGU Fall Meeting,San Francisco,2001
10Garnero E J,Lay T.D shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America.Phys Earth Planet Inter,2003,140:219-242
11Ni S D,Helmberger D V.Horizontal transition from fast to slow structures at the core-mantle boundary,South Atlantic.Earth Planet Sci Lett,2001,187:301-310
12Garnero E J,Vidale J E.ScP:A probe of ultra low velocity zones at the base of the mantle.Geophys Res Lett,1999,26:377-380
13Wen L,Helmberger D V.A2-D P-SV hybrid method and its application to modeling localized structures near the core-mantle boun-dary.J Geophys Res,1998,103:17901-17918
14Wen L,Helmberger D V.Ultra low velocity zones near the core-mantle boundary from broadband PKP precursors.Science,1998,279:1701-1703
15Buffett B A,Garnero E J,Jeanloz R.Sediments at the top of the Earth’s core.Science,2000,290:1338-1342
16Rost S,Revenaugh J S.Seismic detection of rigid zones at the top of the core.Science,2001,294:1911-1914
17Helffrich G,Kaneshima S.Seismological constraints on core composition from Fe-O-S liquid immiscibility.Science,2004,306:2239-2242
18Earle P S,Shearer P M.Observations of PKKP precursors used to estimate small-scale Topography on the core-mantle boundary.Science,1997,277:667-670
19Kennett B L,Engdahl E R.Travel times for global earthquake location and phase identification.Geophys J Int,1991,105:429-465
20Aubert J,Amit H,Hulot G,et al.Thermochemical flows couple the earth’s inner core growth to mantle heterogeneity.Nature,2008,454:758-761
2侯渭,谢鸿森.关于地核和核幔边界区物质的成分及运动特征的研究进展.地球科学进展,1996,11(2):204-208
3唐群署,李丽红.核幔边界D区的地震学研究进展.地学前缘,2006,13(2):213-224
4Kendall J M,Shearer P M.Lateral variations in D thickness from long period shear wave data.J Geophys Res,1994,99(B6):11575-11590
5Rost S,Revenaugh J S.Detection of a D discontinuity in the south Atlantic using PKKP.Geophys Res Lett,2003,30(16):1840
6Rost S,Revenaugh J S.Small scale changes of core mantle boundary reflectivity studied using core reflected PcP.Phys Earth Planet Inter,2004,145:19-36
7Garnero E J,Helmberger D V.Further structural constraints and uncertainties of a thin laterally varying ultra low velocity layer at the base of the mantle.J Geophys Res,1998,103:12495-12509
8Garnero E J,Grand S P,Helmberger D V.Low P-wave velocity at the base of the mantle.Geophys Res Lett,1993,20:1843-1846
9Rost S,Revenaugh J S.Lateral variation of the small scale structure at the CMB west of Tonga-Fiji.AGU Fall Meeting,San Francisco,2001
10Garnero E J,Lay T.D shear velocity heterogeneity,anisotropy and discontinuity structure beneath the Caribbean and Central America.Phys Earth Planet Inter,2003,140:219-242
11Ni S D,Helmberger D V.Horizontal transition from fast to slow structures at the core-mantle boundary,South Atlantic.Earth Planet Sci Lett,2001,187:301-310
12Garnero E J,Vidale J E.ScP:A probe of ultra low velocity zones at the base of the mantle.Geophys Res Lett,1999,26:377-380
13Wen L,Helmberger D V.A2-D P-SV hybrid method and its application to modeling localized structures near the core-mantle boun-dary.J Geophys Res,1998,103:17901-17918
14Wen L,Helmberger D V.Ultra low velocity zones near the core-mantle boundary from broadband PKP precursors.Science,1998,279:1701-1703
15Buffett B A,Garnero E J,Jeanloz R.Sediments at the top of the Earth’s core.Science,2000,290:1338-1342
16Rost S,Revenaugh J S.Seismic detection of rigid zones at the top of the core.Science,2001,294:1911-1914
17Helffrich G,Kaneshima S.Seismological constraints on core composition from Fe-O-S liquid immiscibility.Science,2004,306:2239-2242
18Earle P S,Shearer P M.Observations of PKKP precursors used to estimate small-scale Topography on the core-mantle boundary.Science,1997,277:667-670
19Kennett B L,Engdahl E R.Travel times for global earthquake location and phase identification.Geophys J Int,1991,105:429-465
20Aubert J,Amit H,Hulot G,et al.Thermochemical flows couple the earth’s inner core growth to mantle heterogeneity.Nature,2008,454:758-761
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