地球固体内核平动振荡的研究和检测

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

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。

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.