利用超导重力数据检测日本Mw9.0地震的低频自由振荡及谱线分裂

准确估计低频自由振荡及谱线分裂是约束地球内部结构和改进地球模型的重要手段.本文利用四个不同台站的超导重力观测数据系统研究了日本M_w9.0大地震激发的低于1.5 mHz自由振荡及谱线分裂.研究结果表明:(1)选取适当的数据长度,超导重力观测数据可以检测出低于1.5 mHz除₁S₁以外的所有自由振荡;(2)除₀S₂、₀S₃、₀S₀、₂S₁、₃S₁、₁S₂和₀T₂外,重点探测出₃S₂、₀S₄和₁S₄谱线分裂的所有谱峰;(3)与PREM模型理论频率相比,₀S₀观测频率平均向右偏移0.354×10^-3mHz,说明PREM理论模型中地幔底部参数与真实地球可能存在微小偏差;(4)₃S₂的谱线分裂率r为1.485267,比PREM理论谱线分裂宽度约宽50%,表明PREM中地球内核中部介质参数可能存在一定误差,需要进一步改善.另外,quasi-₀T₂的r为1.254206,比PREM理论谱线分裂宽度约宽25%.

Detecting low-frequency free oscillations and split modes from Japan Mw9.0 earthquake using superconducting gravity observations

It is an important method to estimate low-frequency modes and split modes precisely for constraining the structure of Earth and improving Earth model. Therefore, the free oscillations below 1.5 mHz excited by Japan M_w9.0 earthquake are detected systemically from superconducting observations of four different stations in this paper.The results show that: (1) Based on appropriate length, all the free oscillations, except ₁S₁, below 1.5 mHz can be detected by superconducting observations; (2) In addition to ₀S₂,₀S₃,₀S₀,₂S₁,₃S₁,₁S₂ and ₀T₂, all peaks of split for ₃S₂,₀S₄ and ₁S₄ are detected particularly; (3) Compared with PREM, the observed frequency of ₀S₀ is bigger 0.354×10^-3 mHz. It indicates that there may be small error in the bottom of mantle for PREM; (4) The splitting ratios r of ₃S₂ are 1.485267, about 50% times wider than PREM. It can be deduced from the results that the elastic parameters for center of inner core from PREM need to improve. In additions, the r of quasi-₀T₂ is 1.254206, about 25% times wider than PREM.