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We present a finite-element model of post-seismic solid Earth deformation built in the software package Abaqus (version 2018). The model is global and spherical, includes self-gravitation and is built for the purpose of calculating post-seismic deformation in the far field (>∼300 km) of major earthquakes. An earthquake is simulated by prescribing slip on a fault plane in the mesh and the model relaxes under the resulting change in stress. Both linear Maxwell and biviscous (Burgers) rheological models have been implemented and the model can be easily adapted to include different rheological models and lateral variations in Earth structure, a particular advantage over existing models. We benchmark the model against an analytical coseismic solution and an existing open-source post-seismic model code, demonstrating good agreement for all fault geometries tested. Due to the inclusion of self-gravity, the model has the potential for predicting deformation in response to multiple sources of stress change, for example, changing ice thickness in tectonically active regions.

We present a new, open-source viscoelastic solid earth deformation model, Elmer/Earth. Using the multi-physics finite-element package Elmer, a model to compute viscoelastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts for the restoring force of buoyancy within a system of layers with depth-varying density. It does this by directly integrating the solution of the system rather than by applying stress-jump conditions in the form of Winkler foundations on inter-layer boundaries, as is usually needed when solving the minimization problem given by the stress divergence in commercial codes. We benchmarked the new model with results from a commercial finite-element engineering package (ABAQUS, v2018) and another open-source code that uses viscoelastic normal mode theory, TABOO, using a flat-earth setup loaded by a cylindrical disc of 100 km in diameter and 100 m in height at the density of ice. Evaluating the differences in predicted surface deformation at the centre of the load and two distinctive distances (100 and 200 km), average deviations of 7 and 2.7 cm of Elmer/Earth results to ABAQUS and TABOO, respectively, were observed. In view of more than 100 cm maximum vertical deformation and the different numerical methods and parameters, these are very encouraging results. Elmer is set up as a highly scalable parallel code and distributed under the (L)GPL license, meaning that large-scale computations can be made without any licensing restrictions. Scaling figures presented in this paper show good parallel performance of the new model. Additionally, the high-fidelity ice-sheet code Elmer/Ice utilizes the same source base as Elmer and thereby the new model opens the way to undertaking high-resolution coupled ice-flow–solid-earth deformation simulations, which are required for robust projections of future sea-level rise and glacial isostatic adjustment.

We present a shear wave model of the West Antarctic upper mantle to ∼200 km depth with enhanced regional resolution from the 2016-2018 UK Antarctic Seismic Network. The model is constructed from the combination of fundamental mode Rayleigh wave phase velocities extracted from ambient noise (periods 8-25 s) and earthquake data by two-plane wave analysis (periods 20-143 s). We seek to (i) image and interpret structures against the tectonic evolution of West Antarctica, and (ii) extract information from the seismic model that can serve as boundary conditions in ice sheet and glacial isostatic adjustment modelling efforts. The distribution of low velocity anomalies in the uppermost mantle suggests that recent tectonism in the West Antarctic Rift System (WARS) is mainly concentrated beneath the rift margins and largely confined to the uppermost mantle (

We present a finite-element model of postseismic solid Earth deformation built in the software package ABAQUS (version 2018). The model is global and spherical, and includes self-gravitation and is built for the purpose of calculating postseismic deformation in the far-field (> ~ 300 km) of major earthquakes. An earthquake is simulated by prescribing slip on a fault plane in the mesh and the model relaxes under the resulting change in stress. Both linear Maxwell and biviscous (Burgers) rheological models have been implemented and the model can be easily adapted to include different rheological models and lateral variations in Earth structure, a particular advantage over existing models. We benchmark the model against an analytical coseismic solution and an existing open-source postseismic model, demonstrating good agreement for all fault geometries tested. Due to the inclusion of self-gravity the model has the potential for predicting deformation in response to multiple sources of stress change, for example, changing ice thickness in tectonically active regions.

Large earthquakes in the vicinity of Antarctica have the potential to cause post-seismic deformation on the continent, affecting measurements of displacement and gravity field change from GRACE or those attempting to constrain models of glacial isostatic adjustment.In November 2013 a magnitude 7.7 strike-slip earthquake occurred in the Scotia Sea around 650 km from the northern tip of the Antarctic Peninsula. GPS coordinate time series from the Peninsula region show a change in rate after this event indicating a far-field post-seismic deformation signal is present. At these far-field locations, the effects of fault after-slip are likely negligible and hence we consider the deformation to be due to post-seismic viscoelastic deformation. Here we use a global spherical finite element model to investigate the extent of post-seismic viscoelastic deformation in the northern Antarctic Peninsula. We investigate possible 1D earth models that can fit the GPS data and consider the effect of including a simple 3D earth structure in the region. These results, combined with previous results showing East Antarctica is still deforming following 1998 Mw 8.2 intraplate earthquake, suggest that much of Antarctica is deforming due to recent post-seismic deformation.

Using 8‐25s period Rayleigh and Love wave phase velocity dispersion data extracted from seismic ambient noise, we (i) model the 3D shear wave velocity structure of the West Antarctic crust and (ii) map variations in crustal radial anisotropy. Enhanced regional resolution is offered by the UK Antarctic Seismic Network. In the West Antarctic Rift System (WARS), a ridge of crust ~26‐30km thick extending south from Marie Byrd Land separates domains of more extended crust (~22km thick) in the Ross and Amundsen Sea Embayments, suggesting along‐strike variability in the Cenozoic evolution of the WARS. The southern margin of the WARS is defined along the southern Transantarctic Mountains (TAM) and Haag Nunataks‐Ellsworth Whitmore Mountains (HEW) block by a sharp crustal thickness gradient. Crust ~35‐40km is modelled beneath the Haag Nunataks‐Ellsworth Mountains, decreasing to $\sim$30‐32\,km km thick beneath the Whitmore Mountains, reflecting distinct structural domains within the composite HEW block. Our analysis suggests that the lower crust and potentially the mid crust is positively radially anisotropic (VSH > VSV) across West Antarctica. The strongest anisotropic signature is observed in the HEW block, emphasising its unique provenance amongst West Antarctica's crustal units, and conceivably reflects a ~13\,km thick metasedimentary succession atop Precambrian metamorphic basement. Positive radial anisotropy in the WARS crust is consistent with observations in extensional settings, and likely reflects the lattice‐preferred orientation of minerals such as mica and amphibole by extensional deformation. Our observations support a contention that anisotropy may be ubiquitous in continental crust.

We present a new, open source visco-elastic Earth-deformation model, Elmer/Earth. Using the multi-physics Finite Element package Elmer, a model to compute visco-elastic material deformation has been implemented into the existing linear elasticity solver routine. Unlike approaches often implemented in engineering codes, our solver accounts for the restoring force of buoyancy within a system of layers with depth-varying density. It does this by directly integrating the solution of the system rather than by applying stress-jump conditions in the form of Winkler foundations on inter-layer boundaries, as is usually needed when solving the minimisation problem given by the stress-divergence in commercial codes. We benchmarked the new model with results from a commercial Finite Element engineering package (ABAQUS, v2018) and another open-source code that uses visco-elastic Normal Mode theory, TABOO, using a flat-earth setup loaded by a cylindrical disc of 100 km diameter and 100 m height of ice density. Evaluating the differences of predicted surface deformation at the centre of the load and two distinctive distances (100 km and 200 km), average deviations of 7 cm and 2.7 cm of Elmer/Earth results to ABAQUS and TABOO, respectively, were observed. In view of more than 100 cm maximum vertical deformation and the different numerical methods and parameters, these are very encouraging results. Elmer is set up as a highly scalable parallel code and distributed under the (L)GPL license, meaning that large scale computations can be made without any licensing restrictions. Scaling figures presented in this paper show good parallel performance of the new model. Additionally, the high fidelity ice sheet code Elmer/Ice utilises the same source-base of Elmer and thereby the new model opens the way to undertaking high-resolution coupled ice-flow - Earth deformation simulations, which are required for robust projections of future sea-level rise and glacial isostatic adjustment.

Many studies of Holocene relative sea-level (RSL) changes across Antarctica assume that their reconstructions record uplift from glacial isostatic adjustment caused by the demise of the Last Glacial Maximum (LGM) ice sheets. However, recent analysis of GPS observations suggests that mantle viscosity beneath the Antarctic Peninsula is weaker than previously thought, which would imply that solid Earth motion is not controlled by post-LGM ice-sheet retreat but instead by late Holocene ice-mass changes. If this hypothesis is correct, one might expect to find Holocene RSL records that do not reflect a monotonic decrease in the rate of RSL fall but show variations in the rate of RSL change through the Holocene. We present a new record of late Holocene RSL change from Torgersen Island near Palmer Station in the western Antarctic Peninsula that shows an increase in the rate of relative sea-level fall from 3.0 ± 1.2 mm/yr to 5.1 ± 1.8 mm/yr during the late Holocene. Independent studies of the glacial history of the region provide evidence of ice-sheet changes over similar time scales that may be driving this change. When our RSL records are corrected for sea-surface height changes associated with glacial isostatic adjustment (GIA), the rate of post-0.79 ka land uplift at Torgersen Island, 5.3 ± 1.8 mm/yr, is much higher than the rate of uplift recorded at a nearby GPS site at Palmer Station prior to the Larsen B breakup in 2002 AD (1998-2002 AD

The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain.

Antarctic Peninsula (AP) ice core records indicate significant accumulation increase since 1855, and any resultant ice mass increase has the potential to contribute substantially to present-day glacial isostatic adjustment (GIA). We derive empirical orthogonal functions from climate model output to infer typical spatial patterns of accumulation over the AP and, by combining with ice core records, estimate annual accumulation for the period 1855–2010. In response to this accumulation history, high resolution ice-sheet modeling predicts ice thickness increases of up to 45 m, with the greatest thickening in the northern and western AP. Whilst this thickening is predicted to affect GRACE estimates by no more than 6.2 Gt/yr, it may contribute up to 7 mm/yr to the present-day GIA uplift rate, depending on the chosen Earth model, with a strong east-west gradient across the AP. Its consideration is therefore critical to the interpretation of observed GPS velocities in the AP