Earthquake biases in measurements of Antarctica's sea-level contribution
Earth Observation Research Theme Project
Overview
This project aims to accurately determine Antarctica s contribution to present-day sea-level; this is currently uncertain and controversial (the sign of change is not agreed), with large technique-specific systematic errors.
Three of four measurement techniques rely on knowing the solid earth's changing shape or gravity field. Postseismic deformation has never been considered in such studies, but GPS data now unequivocally show that Antarctica has been deforming since the 1998 Magnitude-8.2 Antarctic Plate Earthquake. We propose to develop a state-of-the-art model of these earthquakes constrained by new and improved geodetic data and then use the model to provide new estimates of Antarctica's contribution to sea-level change.
Find out more about how you can Partner with us or Study with us.
Impact and Engagement
Mass change within the mantle, and associated surface deformation, has long been considered a source of systematic error in ice sheet measurements as it affects three of the four measurement types: laser and radar altimetry and gravimetry. Bedrock uplift alters the measured ice-sheet volume change from altimetry while mantle mass redistribution alters the measured mass change from gravimetry. Gravimetry is particularly sensitive to this systematic signal which is associated with post-seismic deformation and glacial isostatic adjustment (GIA) – the response of the solid Earth to past ice-ocean loading changes.
Antarctica is seismically quiet – the level is not too dissimilar to Australia – and the influence of large earthquakes on mantle mass redistribution and surface deformation has been considered unimportant. As a result, changes in Antarctica’s gravity field have been ascribed purely to present-day changes in ice mass plus GIA– while changes in Antarctica’s shape, as measured by GPS, are ascribed purely to GIA and rigid plate tectonics. Consequently, substantial effort has gone into improving the modelling of mass change due to GIA.
However, CI King’s analysis has revealed that Antarctica is indeed deforming as a result of the 1998 Magnitude-8.2 Antarctic Intra-Plate Earthquake (hereafter referred to as A98) (King and Santamaría-Gómez, GRL, 2016). GPS observations of this deformation recorded at Dumont D’Urville station, located in East Antarctica about 600 km south of the A98 epicentre, show the expected co-seismic step is followed by clear and sustained post-seismic deformation, largely in east, but also in north and the vertical (up) coordinates. Post-seismic deformation as shown here alters not only Earth’s shape but also its gravity field because such deformation is due to large-scale movement of mass within Earth’s mantle.
This discovery means that previous estimates of the Antarctic contribution to sea level are biased, as are measurements of Earth deformation that were previously thought to relate purely to plate tectonic motion and GIA.
Underpinning our approach is the need to 1) develop a new post-seismic model focused on far-field deformations in the context of substantial variations in Earth rheology; and 2) produce an improved dataset to test various model scenarios. This project will provide the first robust quantification of the role of post-seismic deformation in driving ongoing mass transport in Earth’s mantle beneath Antarctica and its effect on measurements of Antarctica’s contribution to sea-level change.
We propose to answer the following research questions (RQs):
RQ1: How widespread is ongoing post-seismic Antarctic deformation associated with large earthquakes?
RQ2: What models of solid Earth post-seismic deformation reproduce the observed changes?
RQ3: How does the modelled deformation alter estimates of the rate and spatial pattern of ice-sheet contribution to sea level?
