The great earthquakes of Sumatra (2004), Maule (2010) and Tohoku (2011) triggered tsunamis as large as a few decimeters over hundreds of kilometer in the open ocean. The mass variation due to the propagating tsunami waves generate a change in the gravity field. In this research report it is demonstrated that such gravity signals can be picked up by the GRACE satellites that orbited the Earth at around 500 km altitude. The tsunamis cause tiny variations in the intersatellite distance between the 2 GRACE satellites. The on-board microwave ranging system was able to detected these variations as inter-satellite acceleration anomalies of up to 1–4 nm/s². There is good agreement between GRACE measurements and tsunami models for the three events.
This research is not intended towards a tsunami early warning system, as satellite gravimetry will never be able to provide the necessary spatial and temporal coverage. Instead, it is meant to demonstrate the very high sensitivity of the GRACE instrumentation in combination with proper data processing.