冰川均衡调整重力与径向位移近似关系的不确定性

根据不同地幔粘滞度的冰川均衡调整(glacial isostatic adjustment, GIA)模型, 研究了地球内部各个圈层对GIA粘性重力扰动速率的贡献, 检验了粘性重力扰动速率与径向位移速率的近似关系及其是否独立于地幔粘滞度, 同时利用绝对重力和GPS(global positioning system)径向位移数据从实测角度对Wahr的近似关系进行比较和验证.结果表明: 岩石圈对GIA重力扰动速率和大地水准面异常速率的贡献都超过了86%, 而岩石圈以下5个圈层的总贡献不大于14%;利用近似关系, 由重力信号转换的径向位移速率与有限元模拟的结果相对差异大约为15%, 且相对差异的大小不依赖于地幔粘滞度的变化; 根据北美绝对重力和GPS径向位移数据得到实测的粘性重力-径向位移比值为0.141±0.014 μGal/mm, 与Wahr的理论值(0.154 μGal/mm)非常接近, 相对差异仅为9.2%.因此, 定量给出了粘性重力-径向位移近似关系的不确定性为9.2%~15.0%, 为利用此近似关系分离GIA和现今地表质量变化粘弹信号的不确定性估计提供了重要参考. 

Uncertainty of Approximate Relationship between GIA Induced Viscous Gravity and Radial Displacement

Based on glacial isostatic adjustment (GIA) models of different mantle viscosities, the contribution from different layers in the earth's interior to the GIA viscous gravity perturbation rates is investigated, and the approximate relation between GIA gravity perturbation rate and uplift rate and whether it is independent of the mantle viscosity are validated in this paper. Furthermore, the Wahr's approximate relation with the data from absolute gravimetry and global positioning system (GPS) was checked. It is found that the contribution of the lithosphere to GIA gravity perturbation rate and geoid anomaly rate is more than 86%, the contribution of the five layers under the lithosphere to GIA gravity signal is less than 14% yet. The relative difference between GIA uplift rate calculated by using approximate relation and that by the finite element method is about 15%, and the difference does not depend on changes in the mantle viscosity. The ratio of gravity versus uplift obtained by ground-based measurements in North America is 0.141±0.014 μGal/mm, which is very close to 0.154 μGal/mm of Wahr's theoretical ratio. The relative difference between the two ratio values above is just 9.2%. Therefore, this study gives the uncertainty value of the Wahr's approximate relation between 9.2%-15.0%, which can be used to evaluate the effects on the results of the separated GIA and present-day mass balance signals.