资源环境科技发展态势分析平台

In regions undergoing glacial isostatic adjustment present-day horizontal surface motion is observed to point mostly, but not always, away from the former ice load. To interpret these observations, we investigate the direction of horizontal velocities using glacial isostatic adjustment models. The direction is controlled by the opposing actions of inward mantle flow and outward lithosphere motion. In contrast with the prevailing idea that glacial isostatic adjustment-induced horizontal velocities point outward, we show that velocities can be either outward or inward. Immediately after deglaciation velocities point inward but change direction to outward after a time that is controlled by mantle viscosity. Present-day horizontal velocities point outward for a uniform mantle viscosity below 1020 Pa s and inward for above 1022 Pa s, with a combination of outward and inward in between. Our results help to interpret GPS-observed horizontal velocities in areas with varying mantle viscosity.

Plain Language Summary The rebound of the Earth following the disappearance of large ice sheets leads to vertical and horizontal movements of the Earth's surface that can be observed with GPS. To explain GPS observations of postglacial rebound with models, it is important to understand how deformation rates depend on the internal structure of the Earth. Here we investigate how the direction of horizontal velocities depends on the viscosity of the mantle using numerical models. The horizontal velocities result from the opposite movements of different layers inside of the Earth. After melting velocities initially point toward the previously glaciated area, but their direction changes after a time that depends on mantle viscosity. Present-day horizontal velocities at the surface point toward the former ice load for a relatively high mantle viscosity, and point away from the former ice load for relatively low viscosities. Our results show that the direction of horizontal velocities derived from GPS observations can provide important information about the Earth's interior.