Postseismic Deformation in the Northern Antarctic Peninsula Following the 2003 and 2013 Scotia Sea Earthquakes

Large earthquakes in the vicinity of Antarctica have the potential to cause postseismic viscoelastic deformation affecting measurements of displacement that are used to constrain models of glacial isostatic adjustment (GIA). In November 2013, a Mw 7.7 strike‐slip earthquake occurred in the Scotia Sea, 650 km from the Antarctic Peninsula. GPS time series from the northern Peninsula show a change in rate after this event, indicating a far‐field postseismic deformation signal is present. In this study, we use a finite element model with a suite of 1D and 3D Earth structures to investigate the extent of postseismic deformation in the Antarctic Peninsula. Model output is compared with GPS time series to place constraints on the Earth structure in this region. The preferred Earth structure has a thin lithosphere combined with a Burgers rheology with steady‐state viscosity of 4 × 10 18 Pa s and transient viscosity one order of magnitude lower. Our study shows that including 3D Earth structure does not improve the fit. Using the best fitting Earth structure, we run a forward model of the nearby 2003 Mw 7.6 strike‐slip earthquake and combine the predictions for both earthquakes. We show that postseismic deformation is widespread across the northern Peninsula with rates of horizontal deformation up to 1.65 mm/yr for the period 2015–2020, a signal that persists for decades. These results suggest that much of Antarctica may be deforming due to recent postseismic deformation and this signal needs to be accounted for when using GPS observations to constrain geophysical models. Antarctica is not well‐known for earthquakes and consequently there are very few studies on the subject. However, large earthquakes that have occurred some 100s km from the coastline have the potential to cause deformation within the continent as the Earth undergoes far‐field postseismic viscoelastic relaxation in response to the large stress changes in the decades following an earthquake. In this study, we examine two earthquakes that occurred in the Scotia Sea around 650 km from the northern tip of the Antarctic Peninsula in 2003 and 2013. GPS observations from the Northern Antarctic Peninsula show a change in deformation rate following the 2013 earthquake. We use the time series to constrain a finite element model of postseismic deformation to constrain the underlying Earth properties. Using this model to predict ongoing deformation due to the 2003 and 2013 earthquakes gives an estimated combi