罗斯海海域大地水准面异常的成因研究

Study on the origin of geoid anomalies in the Ross Sea area

本文利用数值法求解瞬时地幔对流问题以模拟大地水准面异常.利用两个较新的S波速度异常层析模型SEMUCB_WM1和TX2019slab,将其转换为密度异常作为控制方程的浮力驱动项;采取的黏度结构模型中,上下地幔的黏度比为1∶50.为了研究地幔不同结构对罗斯海海域大地水准面异常的影响,分别提取上、下地幔的密度异常正/负值,作为对流控制方程的输入项,计算相应的模拟大地水准面异常.将模拟大地水准面异常与观测值进行对比,发现罗斯海海域的大地水准面异常主要来自下地幔及上地幔的负密度(波速)异常,下地幔正密度异常对该区域大地水准面负异常也有一定的贡献.本文认为,地幔密度负异常在罗斯海海域大地水准面异常的形成中占据主导作用,地幔对流的动力学效应对该区域大地水准面异常的形成影响较弱.

In this paper,a numerical method is used to solve the instantaneous mantle convection to simulate geoid anomalies.Two recent S-wave velocity anomaly tomography models-SEMUCB_WM1 and TX2019slab are employed to convert geoid anomalies into density anomalies as the buoyancy driving term in the governing equation.The viscosity ratio of the upper and lower mantle used in this study is 1∶50.In order to study the influence of different structures of the mantle on geoid anomalies in the Ross Sea area,the positive/negative density anomalies of the upper and lower mantles are extracted respectively as input terms in the convection governing equations,and then geoid anomalies are calculated.Comparing the modeling geoid anomalies with observations shows that the geoid anomalies in the Ross Sea area mainly come from the negative density(seismic wave velocity)anomalies of the lower and upper mantle,and the positive density anomalies in the lower mantle also has a certain contribution to the negative geoid anomalies in this area.We suggest that negative mantle density anomalies play a dominant role in the formation of geoid anomalies in the Ross Sea,and the dynamic effect of mantle convection has a smaller influence on the formation of geoid anomalies in this area.