核幔边界地幔侧不同尺度横向非均匀对地球自由振荡的影响

Influence of different scales of lateral inhomogeneous structures on the mantle side of the CMB on the Earth's free oscillation

地球自由振荡携带着丰富的地球内部结构信息,地球内部核幔边界的横向非均匀性问题是当今地球物理学相关学科研究的热点和难点.为了研究不同尺度横向非均匀结构对地球自由振荡的影响,本文在PREM地球模型中分别引入具有横向非均匀结构的D"区和超低速异常带(ULVZ),构建了有针对性的、新的不同尺度横向非均匀结构地球模型,采用波动方程的谱元解法开展地球自由振荡与地震波传播的长时程数值模拟、频谱分析及功率谱密度分析,以评估不同尺度横向非均匀结构对地球自由振荡的影响,从而为研究地球自由振荡的影响因素、优化地球内部结构模型等提供参考.本文的数值结果及其分析显示,除0S27、0S28、0S29和0S30振型外,核幔边界的这两类横向非均匀结构对自由振荡大部分基频振型的特征频率几无影响,仅对幅值有不同程度的影响.这一结果表明:基频振型中0S27、0S28、0S29和0S30振型适合于利用地球自由振荡谱线分裂现象分析核幔边界地幔侧横向非均匀结构的研究,而其余基频振型则不适合此类研究.

Earth＇s free oscillation carries a lot of information on the structure of the Earth interior.The lateral heterogeneities of the core-mantle boundary is a focused and difficult problem in the research field of geophysics.In order to distinguish and study the influence of different scales of lateral heterogeneitieson the Earth＇s free oscillation,we introduce the D＂ zone and the ultra-low-velocityzone into the PREM,and construct two models with different scales of lateral heterogeneities structures.Following the models,we conduct long-time computation,spectral analysis and power spectral density analysis of Earth＇s free oscillation and propagation of seismic waves using the spectral element method（SEM）.Based on these results of the influence of different-scale lateral heterogeneitieson the Earth＇s free oscillation,we can provide a reference to the study of the Earth＇s free oscillation and to the majorization of the Earth ＇s internal structure models.Numerical results and analysis shows that the two types of lateral heterogeneities have little effect on the characteristic frequencies of most of the fundamental oscillations of free oscillations except for the modes 0S27,0S28,0S29 and 0S30.However,the two types of lateral heterogeneities have different influence on the amplitude.This means mode 0S27,0S28,0S29 and 0S30 are suitable for the analysis of lateral heterogeneities of the core-mantle boundary by using the free oscillating spectral splitting of the earth.While the rest of the fundamental modes are not suitable for such research.