Impact of the solid Earth mass adjustment by the 2011 Tohoku-Oki earthquake on the regional sea level and hydrological mass change recovery from GRACE

For more than a decade, GRACE data have provided global mass redistribution measurements due to water cycles, climate change and giant earthquake events. Large earthquakes can yield gravity changes over thousands of kilometres from the epicentre for years to decades, and those solid Earth deformation signals can introduce significant biases in the estimate of regional-scale water and ice mass changes around the epicentres. We suggest a modelling scheme to understand their contribution to the estimates of water and ice mass changes and to remove the earthquake-related solid mass signals from GRACE data. This approach is composed of physics-based earthquake modelling, GRACE data correction and high-resolution surface mass change recovery. In this study, we examined the case of the 2011 Tohoku-Oki earthquake to better estimate the regional sea level and hydrological mass changes in the East Asia. The co- and post-seismic changes from GRACE observations were used to constrain the earthquake model parameters to obtain optimal self-consistent models for the earthquake source and the asthenosphere rheology. The result demonstrated that our earthquake correction model significantly reduced the mass change signals by solid Earth deformation from the time-series of regional surface mass changes on both land and oceans. For example, the apparent climate-related ocean mass increase over the East Sea was 1.59 & PLUSMN; 0.11 mm yr(-1) for 2003-2016, significantly lower than the global mean ocean mass trend (2.04 & PLUSMN; 0.10 mm yr(-1)) due to contamination of the earthquake signals. After accounting for the solid mass changes by the earthquake, the estimate was revised to 1.87 & PLUSMN; 0.11 mm yr(-1), that is increased by 20 per cent and insignificantly different from the global estimate.