The robustness of geodetically derived 1-D Antarctic viscosity models in the presence of complex 3-D viscoelastic Earth structure
The robustness of geodetically derived 1-D Antarctic viscosity models in the presence of complex 3-D viscoelastic Earth structure
复制标题
在存在复杂的 3-D 粘弹性地球结构的情况下，大地测量得出的 1-D 南极粘度模型的稳健性
DOI：
10.1093/gji/ggac129
复制
发表时间：
2022
影响因子：
2.8
通讯作者：
Mitrovica, J. X.
中科院分区：
文献类型：
--
作者：
Powell, E.;Latychev, K.;Gomez, N.;Mitrovica, J. X.
南极下方的地球结构对冰盖的演化起着重要的控制作用。一系列地质和地球物理数据集表明，这一结构很复杂，西段的岩石圈厚度为50-100千米，上地幔内的粘度变化2-3个数量级。最近对利用全球导航卫星系统(GNSS)观测估计的抬升速率的分析推断，利用冰川均衡调整正演模型(GIA)，南极洲西部以下的一维粘性剖面离散成上地幔内的一小组层。然而，目前尚不清楚这些一维粘度模型在一个具有复杂三维地幔结构的地区代表了什么，以及它们适用于什么地理长度尺度。在这里，我们通过重复相同的建模程序来探索这个问题，但应用于使用从该地区的地震层析成像推断的三维粘弹性地球结构的现实模型计算的合成隆起率、捕捉这种复杂性的GIA的有限体积处理以及推断的1992-2017年期间南极冰块的加载历史。我们发现，通过用于生成合成材料的三维粘性场，最佳拟合的一维推论和区域平均深度剖面之间存在高达一个数量级的差异。额外的计算表明，如果增加分析中采用的观测点的数量，这种分歧程度不会得到系统的改善。此外，从这种过程中推断出的一维模型不是唯一的，也就是说，由于各层内粘性值之间的相关性，大范围的粘性剖面同样符合合成提升率。虽然每个GNSS站点的抬升速率对复杂的三维粘性场子空间很敏感，但基于近端站点子集的速率的额外分析表明，一维推断中的偏差水平没有得到一致的改善。我们还得出结论，由三维模型产生的广泛的区域尺度的隆起场不能很好地被基于最佳拟合的一维地球模型的预测所代表。今后分析全球导航卫星系统数据的工作应扩大到包括水平速率，并转向反映数据内在三维分辨率的三维结构的反演。
Earth structure beneath the Antarctic exerts an important control on the evolution of the ice sheet. A range of geological and geophysical data sets indicate that this structure is complex, with the western sector characterized by a lithosphere of thickness ∼50–100 km and viscosities within the upper mantle that vary by 2–3 orders of magnitude. Recent analyses of uplift rates estimated using Global Navigation Satellite System (GNSS) observations have inferred 1-D viscosity profiles below West Antarctica discretized into a small set of layers within the upper mantle using forward modelling of glacial isostatic adjustment (GIA). It remains unclear, however, what these 1-D viscosity models represent in an area with complex 3-D mantle structure, and over what geographic length-scale they are applicable. Here, we explore this issue by repeating the same modelling procedure but applied to synthetic uplift rates computed using a realistic model of 3-D viscoelastic Earth structure inferred from seismic tomographic imaging of the region, a finite volume treatment of GIA that captures this complexity, and a loading history of Antarctic ice mass changes inferred over the period 1992–2017. We find differences of up to an order of magnitude between the best-fitting 1-D inferences and regionally averaged depth profiles through the 3-D viscosity field used to generate the synthetics. Additional calculations suggest that this level of disagreement is not systematically improved if one increases the number of observation sites adopted in the analysis. Moreover, the 1-D models inferred from such a procedure are non-unique, that is a broad range of viscosity profiles fit the synthetic uplift rates equally well as a consequence, in part, of correlations between the viscosity values within each layer. While the uplift rate at each GNSS site is sensitive to a unique subspace of the complex, 3-D viscosity field, additional analyses based on rates from subsets of proximal sites showed no consistent improvement in the level of bias in the 1-D inference. We also conclude that the broad, regional-scale uplift field generated with the 3-D model is poorly represented by a prediction based on the best-fitting 1-D Earth model. Future work analysing GNSS data should be extended to include horizontal rates and move towards inversions for 3-D structure that reflect the intrinsic 3-D resolving power of the data.