Large earthquakes do not only heavily deform the crust in the vicinity of the fault, they also change the gravity field of the area affected by the earthquake due to mass redistribution in the upper layers of the Earth. Besides that, for sub-oceanic earthquakes deformation of the ocean floor causes relative sea-level changes and mass redistribution of water that has again a significant effect on the gravity field. Such a sub-oceanic earthquake occurred on 27 February 2010 in central Chili with a magnitude of Mw 8.8 and on 11 March 2011 with a magnitude of Mw 9.0 near the east coast of Honshu, Japan. This makes both a potential candidate for detecting the co-seismic gravity changes in the GOCE gradiometer data. We will assess the detectability of gravity field changes in the GOCE gravity gradients by modelling these earthquakes using a forward model as well as taking differences of of GOCE data before and after the respective earthquakes.