内核地震波速各向异性的成因
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摘要
地球内核是轴对称各向异性的，其对称轴与地球的极轴之间有１１°左右的夹角，本 文根据地球内核相对于外部地球有差异转动这一观测结果，利用晶体生长理论，对内核地震波 速度各向异性的成因进行了探讨．当从熔融状态结晶时，晶体的生长速度与晶体和熔融态之 间相对运动的线速度成正比涸此当固态内核在液态外核中生长时，沿赤道方向的生长速度比 两极方向快．在万有引力场的作用下内核始终保持近似球形，生长速度较快的赤道附近的物 质会向两极区域流动，形成轴对称的流变场。这一轴对称的流变场伴随着轴对称的应力场，使 得构成地球内核的ｈｃｐ型铁晶体的ｃ轴沿着内核自转轴的方向排列，导致观测到的地球内核地 震波速度各向异性。作为推论，内核相对于外部地球可能同时存在着进动和章动。
The earth inner core is axisymmetric seismic anisotropy, and there is an angle of about 11° between the symmetric axis of the inner core's seismic anisotropy and the earth axis. In this whole, we discussed the origin of this anisotropy, basing on the observation of differential rotation between the solid inner core and the molten outer core. According to the theory on crystal growth from motion status, the crystal growth speed is proportional to the relative linear speed between the solid and the molten crystals. As a result the inner core grows faster at the equator than at polar area. Under the action of gravitational force, the inner core remains quasi--orbicular. Consequenlly the material will flow from the equator to the polar area, resulting in an axial symmetric viscous flow. This flow is accompanied by an axial symmetric stress field, which align c-axes of hcp iron along the inner core's rotation axis, resulting in observed seismic anisotropy. As a deduction, there may be a notation as well as a precession of the inner core relative to the outer earth.
The earth inner core is axisymmetric seismic anisotropy, and there is an angle of about 11° between the symmetric axis of the inner core's seismic anisotropy and the earth axis. In this whole, we discussed the origin of this anisotropy, basing on the observation of differential rotation between the solid inner core and the molten outer core. According to the theory on crystal growth from motion status, the crystal growth speed is proportional to the relative linear speed between the solid and the molten crystals. As a result the inner core grows faster at the equator than at polar area. Under the action of gravitational force, the inner core remains quasi--orbicular. Consequenlly the material will flow from the equator to the polar area, resulting in an axial symmetric viscous flow. This flow is accompanied by an axial symmetric stress field, which align c-axes of hcp iron along the inner core's rotation axis, resulting in observed seismic anisotropy. As a deduction, there may be a notation as well as a precession of the inner core relative to the outer earth.
引文
[ 1 ] Stixrude L, Cohen R E. High-pressure elasticity of iron and anisotropy of earth's inner core. Science,1995, 267: 1972-1975.
[ 2 ] Sayers C M. The crystal structure of iron in the Earth's inner core. Geophys. J Int., 1990, 103:285--286.
[3 ] Yoshida S, Sumita I, Kumazawa M. Growth model of the inner core coupled with the outer core dynamicsand the resulting elastic anisotropy. J. Geophy. Res., 1996, 101(B12):28085--28103.
[ 4 ] Stixrude L, Cohen R E. Constraints on the crystalline structure of the inner core: Mechanical instability ofBCC iron at high pressure. Geophys. Res. Lett., 1995, 22(2):125--128.
[ 5 ] Boehler R, Bargen N, Chopelas A. Melting, thermal expansion, and phase transitions of iron at highpressures. J. Geophy. Res., 1990, 95(B13):21731--21736.
[ 6 ] Wenk H R Preferred Orientation in Deformed Metals and Rocks: An Introduction to Modern TextureAnalysis. New York: Academic Press, Inc., 1985.
[ 7 ] Song X D, Richards P G.. Seismological evidence for differential rotation of the Earth's inner core. Nature,1996, 382: 221-224.
[ 8 ] Su W, Dziewonski A M, Jeanloz K Planet within a Planet: Rotation of the inner core of Earth. Science,1996, 274: 1883-1887.
[9]潘普林BR晶体生长.北京:中国建筑工业出版社,1981.146-148.Pampin, B. K. Crystal Growth (in Chinese). Beijing: China Construction Industry Press, 1981, 146--148.
[10] Kamb W B. Theory of preferred crystal orientation developed by crystallization under stress. J. Geol.,1959, 67: 153~170.
[11] Kamb W B. The thermodynamic theory of nonhydrostatically stressed solids. J. Geophys. Res., 1961, 66:259--271
[12]刘青松,朱日祥,潘永信等.地球磁场偶极子和非偶极子分量变化特征及其相关的地球深部过程.地球物理学报,1999,42(2);178-184。LIU Qing-Song, ZHU Ri-Xiang, PAN Yong-Xin, et al. Secular variations in geomagnetic dipole andnon-dipole components: constrains on the earth's interior process. Chinese J Geophys. (in Chinese), 1999,42(2): 1 78~ 184.
[13]马石庄.旋转分层导电电流体双扩散磁流体力学不稳定性.地球物理学报,1993,36(5);579-588.MA Shi-Zhuang. Double-diffusive and MHD instabilities in a rotaing stratified conducting fluid layer.Chinese J- Geophys. (in Chinese), 1993, 36(5);579--588.
[14]李光品,傅容珊.核幔边界的动力学背景.地球物理学报,1996,38(4):548—552.LI Guang-Pin, FU Rong-Shan. Dynamic background in core-mantle boundary. Chinese J. Geophys. (inChinese), 1996, 38(4):548-552.
[15] Stacey F D.地球物理学.北京:地震出版社,1981 245.Stacey F D. Physicsof the Earth (in Chinese);Beijing: Scismological Press, 1981. 245.
[16]兰泊克K地球自转的变化、北京;地震出版社,1988.28.Lanbech N Change of the earth’s rotation(in Chinese), Beijing: Seismological Press, 1988. 28。
[ 2 ] Sayers C M. The crystal structure of iron in the Earth's inner core. Geophys. J Int., 1990, 103:285--286.
[3 ] Yoshida S, Sumita I, Kumazawa M. Growth model of the inner core coupled with the outer core dynamicsand the resulting elastic anisotropy. J. Geophy. Res., 1996, 101(B12):28085--28103.
[ 4 ] Stixrude L, Cohen R E. Constraints on the crystalline structure of the inner core: Mechanical instability ofBCC iron at high pressure. Geophys. Res. Lett., 1995, 22(2):125--128.
[ 5 ] Boehler R, Bargen N, Chopelas A. Melting, thermal expansion, and phase transitions of iron at highpressures. J. Geophy. Res., 1990, 95(B13):21731--21736.
[ 6 ] Wenk H R Preferred Orientation in Deformed Metals and Rocks: An Introduction to Modern TextureAnalysis. New York: Academic Press, Inc., 1985.
[ 7 ] Song X D, Richards P G.. Seismological evidence for differential rotation of the Earth's inner core. Nature,1996, 382: 221-224.
[ 8 ] Su W, Dziewonski A M, Jeanloz K Planet within a Planet: Rotation of the inner core of Earth. Science,1996, 274: 1883-1887.
[9]潘普林BR晶体生长.北京:中国建筑工业出版社,1981.146-148.Pampin, B. K. Crystal Growth (in Chinese). Beijing: China Construction Industry Press, 1981, 146--148.
[10] Kamb W B. Theory of preferred crystal orientation developed by crystallization under stress. J. Geol.,1959, 67: 153~170.
[11] Kamb W B. The thermodynamic theory of nonhydrostatically stressed solids. J. Geophys. Res., 1961, 66:259--271
[12]刘青松,朱日祥,潘永信等.地球磁场偶极子和非偶极子分量变化特征及其相关的地球深部过程.地球物理学报,1999,42(2);178-184。LIU Qing-Song, ZHU Ri-Xiang, PAN Yong-Xin, et al. Secular variations in geomagnetic dipole andnon-dipole components: constrains on the earth's interior process. Chinese J Geophys. (in Chinese), 1999,42(2): 1 78~ 184.
[13]马石庄.旋转分层导电电流体双扩散磁流体力学不稳定性.地球物理学报,1993,36(5);579-588.MA Shi-Zhuang. Double-diffusive and MHD instabilities in a rotaing stratified conducting fluid layer.Chinese J- Geophys. (in Chinese), 1993, 36(5);579--588.
[14]李光品,傅容珊.核幔边界的动力学背景.地球物理学报,1996,38(4):548—552.LI Guang-Pin, FU Rong-Shan. Dynamic background in core-mantle boundary. Chinese J. Geophys. (inChinese), 1996, 38(4):548-552.
[15] Stacey F D.地球物理学.北京:地震出版社,1981 245.Stacey F D. Physicsof the Earth (in Chinese);Beijing: Scismological Press, 1981. 245.
[16]兰泊克K地球自转的变化、北京;地震出版社,1988.28.Lanbech N Change of the earth’s rotation(in Chinese), Beijing: Seismological Press, 1988. 28。
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