| Summary: | PhD Thesis The two main causes of the long-term deformation of the Earth on a global scale are tectonic plate motion and Glacial Isostatic Adjustment (GIA). GIA results in vertical as well as lateral movements of the Earth’s surface. It is difficult to distinguish from local and regional effects, such as the deformational response to decadal and longer-term changes in continental water storage and the mass balance of glaciers and ice sheets. On a global scale, GIA is also, to some extent, difficult to distinguish from millennial-term lateral motion due to plate tectonics. The effects of GIA must therefore be modelled. GIA models use an ice sheet history combined with an estimate for Earth rheology to produce predictions of present-day GIA velocities. GIA models are typically tuned to fit evidence for past and present vertical motion, as determined from historical relative sea-level data, and they may additionally be tuned to fit GNSS-derived present-day uplift rates. However, GNSS-derived horizontal rates have not traditionally been used to tune GIA models. Lateral Earth structure can significantly influence horizontal GIA rates, and most GIA models do not account for lateral structure, these are so-called 1D GIA models. Recently, GIA models accounting for lateral Earth structure have been developed, known as 3D GIA models. Vertical GIA velocities are important for studies of surface mass loading, sea-level change, mass balance of glaciers and ice sheets, and vertical reference systems. Horizontal GIA velocities are also important for interpreting surface mass loading, as well as tectonic plate rigidity, with implications for horizontal components of reference systems. Consequently, this project aims to create a bespoke 3D GNSS surface velocity field to test and compare a set of recent 1D and 3D GIA models and investigate tectonic plate motion. In turn, this velocity field has several applications beyond this project. It may be used to investigate present-day surface loading due to ice melting as well as other ...
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