地球固体内核平动振荡的研究和检测

doi:10.11867/j.issn.1001-8166.2005.07.0740

地球科学进展 ›› 2005, Vol. 20 ›› Issue (7): 740 -745. doi: 10.11867/j.issn.1001-8166.2005.07.0740

地球固体内核平动振荡的研究和检测

徐建桥 ^1,2，孙和平 ¹，傅容珊 ²

1.中国科学院测量与地球物理研究所动力大地测量学重点开放实验室，湖北武汉 430077；2.中国科学技术大学地球和空间科学学院，安徽合肥 230026

收稿日期:2004-07-13 修回日期:2005-03-03 出版日期:2005-07-25
通讯作者: 徐建桥
基金资助:
中国科学院知识创新工程重要方向项目“地球深内部结构和动力学研究”(编号：KZCX3-SW-131)资助．

DETECTION AND STUDY OF THE TRANSLATIONAL OSCILLATIONS OF THE EARTH’S SOLID INNER CORE

XU Jianqiao ^1,2;SUN Heping ¹;FU Rongshan ²

1.Key Laboratory of Dynamic Geodesy,Institute of Geodesy and Geophysics,Chinese Academy of Sciences,Wuhan 430077,China;2.College of Earth and Space Sciences, University of Science and Technology of China,Hefei 230026, China

Received:2004-07-13 Revised:2005-03-03 Online:2005-07-25 Published:2005-07-25

下载PDF ( 1436 )

系统介绍了有关Slichter模的理论模拟及其超导重力观测检测的进展。地球固态内核的平动振荡是地球的基本简正模之一，又称Slichter模，以重力作为主要恢复力，其本征周期大约为几个小时。从理论模拟结果看，Slichter模的本征周期对于ICB密度差最为敏感，而ICB附近外核流体的粘滞性、内外核之间的过渡层以及Lorentz力等因素对周期的影响很小，Slichter模的研究和检测为了解地球中心附近的密度结构提供重要的信息。

关键词: Slichter模, 本征频率, 内核边界密度差, 理论模拟, 超导重力检测

The advances of the theoretical modeling and detection with the superconducting gravimeters (SGs), related to the Slichter triplet, are systematically introduced in this paper. The translational oscillations of the Earth’s solid inner core, which is usually called as the Slichter modes in honor of the scientist who firstly pointed out its theoretical existence, are a triplet of the principle normal modes of the Earth. The triplet is primarily driven by the gravitational forces and has eigenperiods of several hours. From the theoretical modeling, it is found that the eigenperiods of the Slichter modes are most sensitive to the density contrast across the inner core boundary (ICB), and are only slightly disturbed by the viscosity of the fluid near the ICB, the transitional zone between the outer and inner cores, Lorentz forces and some others effects. Therefore, study and detection of the Slichter modes may provide significant information about the structure of the Earth’s deep interior. Due to less knowledge to the Earth’s deep interior, there exists great uncertainty in the results of theoretical modeling based on the present Earth’s models. It is necessary to detect the signatures related to the Slichter modes by using the ground-based observations. Smylie (1992) claimed that the weak gravity resonance signatures, coming from the Slichter triplet, were found in the SG data from plural stations in the central Europe. Based on the results, the density and viscosity near the ICB have been evaluated. However, thses results were questioned by the other scientists. Recently, we have comprehensively analyzed and treated the continuous long-term SG data from the worldwide network of the Global Geodynamics Projects. It is found that there is no evidence to support the existence of the resonance related to the Slichter triplet as what Smylie claimed. On the contrary, it is found that there are eight significant spectral peaks related to some globally geodynamical phenomena, and the Slichter triplet is one of their possible resources. 

Key words: Slichter triplet, Eigenperiods, Density contrast across the inner core boundary, Theoretical modeling, Detection with the superconducting gravimeters

中图分类号:

P312

[1] Souriau A, Souriau M. Ellipticity and density at the inner core boundary from subcritical PKiKP and PcP data[J]. Geophysical Journal International, 1989, 98: 39-54.
[2] Shearer P, Master G. The density and shear velocity contrast at the inner core boundary [J]. Geophysical Journal International, 1990, 102: 491-498.
[3] Slichter L B. The fundamental free mode of the Earth’s inner core [J]. Proceedings of the National Academy of Sciences, USA, 1961, 47: 186-190.
[4] Busse F H. On the free oscillation of the Earth’s inner core [J]. Journal of Geophysical Research, 1974, 79: 753-757.
[5] Crossley D, Rochester M, Peng Z. Slichter modes and Love numbers [J]. Geophysical Research Letters, 1992, 19: 1 679-1 682.
[6] Rieutord M. Slichter modes of the Earth revisited [J]. Geophysics of the Earth and Planetary Interiors, 2002, 131: 269-278.
[7] Rogister V. Splitting of seismic-free oscillations and of the Slichter triplet using the normal mode theory of a rotating, ellipsoidal Earth [J]. Geophysics of the Earth and Planetary Interiors, 2003, 140: 169-182.
[8] Crossley D J. Core undertones with rotation[J]. Geophysical Journal of the Royal Astronomical Society, 1975, 42: 477-488.
[9] Smith M L. The scalar equations of infinitesimal elastic-gravitational motion for a rotating, slightly elliptical Earth[J]. Geophysical Journal of the Royal Astronomical Society, 1974, 37: 491-526.
[10] Smith M L. Translational inner core oscillations of a rotating, slightly elliptical Earth[J]. Journal of Geophysical Research, 1976, 81: 3 055-3 064.
[11] Dahlen F A. The normal modes of a rotating, elliptical Earth[J]. Geophysical Journal of the Royal Astronomical Society, 1968, 16: 329-367.
[12] Dahlen F A, Sailor R V. Rotational and elliptical splitting of the free oscillation of the Earth[J]. Geophysical Journal of the Royal Astronomical Society, 1979, 58: 609-623.
[13] Crossley D J, Hinderer J, Legros H. On the excitation, detection and damping of core modes [J]. Geophysics of the Earth and Planetary Interiors, 1991, 68: 97-116.
[14] Richter B. Parallel registration with two superconducting gravimeters[J]. Bulletin D’informations de Marées Terrestres, 1987, 99: 6 757-6 758.
[15] Xu Jianqiao, Sun Heping, Fu Rongshan. Detection of long-period core modes by using the global superconducting gravimeter data [J]. Chinese Journal Geophysics, 2005, 48(1): 69-77.[徐建桥, 孙和平, 傅容珊. 利用全球超导重力仪数据检测长周期核模[J]. 地球物理学报, 2005, 48(1): 69-77.]
[16] Sun Heping, Xu Houze. Execution and prospect for the Global Geodynamics Project cooperation[J]. Advances in Earth Science, 1997, 12(2): 152-157.[孙和平,许厚泽. 国际地球动力学合作项目的实施与展望[J]. 地球科学进展,1997, 12(2): 152-157.]
[17] Xu Jianqiao, Sun Heping. Advances in the study on the effects of the Earth’s fluid outer core[J]. Advances in Earth Science, 2002, 16(5): 664-669.[徐建桥,孙和平.地球液核的动力学效应研究进展[J]. 地球科学进展, 2002, 16(5): 664-669.]
[18] Smylie D E, Jiang X, Brennan B J, et al. Numerical calculation of modes of oscillation of the Earth’s core[J]. Geophysical Journal International, 1992,108: 465-490.
[19] Rochester M, Peng Z. The Slichter modes of the rotating Earth: A test the subseismic approximation[J]. Geophysical Journal International,1993, 113: 575-585.
[20] Buffett B, Geortz D. Magnetic damping of the translational oscilation of the inner core [J]. Geophysical Journal International, 1995,120: 103-110.
[21] Peng Z. Effects of a mushy transition zone at the inner core boundary on Slichter modes [J]. Geophysical Journal International, 1997,131: 607-617.[22] Smylie D E, MacMillan D G. The inner core as a dynamoic viscometer[J].Geophysics of the Earth and Planetary Interiors, 2000, 117: 71-79.
[23] Smylie D E. The inner core translational triplet and the density near Earth’s center[J]. Science, 1992, 255: 1 678-1 682.
[24] Smylie D E, Hinderer J, Richter B, et al. The product spectra of gravity and barometric pressure in Europe[J]. Geophysics of the Earth and Planetary Interiors, 1993, 80: 135-157.
[25] Smylie D E, Jiang X. Core oscillations and their detection in superconducting gravimeter records [J]. Journal of Geomagnetism and Geoelectricity, 1993, 45: 1 347-1 369.
[26] Jensen O, Hinderer J, Croddley D J. Noise limitations in the core-mode band of superconducting gravimeter data[J]. Geophysics of the Earth and Planetary Interiors, 1995, 90: 169-181.
[27] Hinderer J, Crossley D, Jensen O. A search for the Slichter triplet in superconducting gravimeter data[J]. Geophysics of the Earth and Planetary Interiors, 1995, 90: 183-195.
[28] Smylie D E. Viscosity near the Earth’s solid inner core[J]. Science, 1999, 284: 461-463.
[29] Courtier N, Ducarme B, Goodkind J, et al. Global superconducting gravimeter observations and the search for the translational modes of the inner core[J]. Geophysics of the Earth and Planetary Interiors, 2000, 117: 3-20.
[30] Sun H, Xu J, Ducarme B. Search for the translational triplet of the Earth’s solid inner core by SG observations at GGP stations [J].Bulletin d’Informations de Marées Terrestres, 2003, 138: 10 977-10 985.
[31] Rosat S, Hinderer J, Crossley D, et al. The search for the Slichter mode: Comparison of noise level of superconducting gravimeters and investigation of a stacking method [J]. Geophysics of the Earth and Planetary Interiors, 2003, 140: 183-202.
[32] Sun Heping, Xu Jianqiao, Ducarme B. Detection of the translational oscillations of the Earth’s solid inner core based on the international superconducting gravimeter observations [J]. Chinese Science Bulletin, 2004, 49(11): 1 165-1 176.[孙和平,徐建桥, Ducarme B.基于国际超导重力仪观测资料检测地球固态内核的平动振荡[J].科学通报, 2004, 49(8): 803-813. ]
[33] Johnson I M, Smylie D E. A variational approach to whole Earth dynamics[J]. Geophysical Journal of the Royal Astronomical Society, 1977, 50: 35-54.
[34] Wu W J, Rochester M G. Core dynamics: The two-potential description and a new variational priciple[J]. Geophysical Journal International, 1990, 103: 697-706.
[35] Xu Jianqiao, Sun Heping, Fu Rongshan. Variational approach to free motion in the Earth’s fluid outer core [J]. Chinese Journal of Geophysics, 2004,47(1): 61-74.[徐建桥, 孙和平, 傅容珊. 液核自由运动的变分方法[J]. 地球物理学报, 2004, 47(1): 61-74.]
[36] Smylie D E, Rochester M G. Compressibility, core dynamics and the subseismic wave equation[J]. Geophysics of the Earth and Planetary Interiors, 1981, 24: 308-319.
[37] Smylie D E, Szeto A M K, Sato K. Elastic boundary conditions in long-period core oscillations [J]. Geophysical Journal International, 1990, 100: 183-192.
[38] Crossley D J, Rochester M G. The subseismic approximation in core dynamics [J]. Geophysical Journal International, 1992, 108: 506-508.
[39] Xu Jianqiao, Sun Heping. Earth’s deformation due to the dynamical perturbations of the fluid outer core [J]. Acta Seismologica Sinca, 2002, 15(4): 414-424.[徐建桥,孙和平.液核动力学扰动引起的地球形变[J].地震学报, 2002, 24(4): 397-406.]

[1]	张赤军. 全球垂直基准研究中的几点思考[J]. 地球科学进展, 2000, 15(1): 106-109.

阅读次数

全文

摘要