The European Space Agency's GOCE satellite has revealed that the devastating 2011 Japanese earthquake left its mark in Earth's gravity”another example of the extraordinary mission surpassing its original scope.
GOCE mapped Earth's gravity with unrivalled precision for more than four years, but nobody expected the data to show changes over time. Now careful analysis shows the effects of the 9.0 earthquake that struck east of Japan's Honshu Island on March 11, 2011, clearly are visible in GOCE's gravity data.
Large earthquakes deform Earth's crust and cause tiny changes in local gravity. The strength of gravity varies from place to place on our planet's surface, and it was GOCE's task to map these variations precisely.
There are several reasons why values of gravity differ, but one is a consequence of material inside Earth being inhomogeneous and unevenly distributed. Because earthquakes shift around rock and other material tens of kilometers below the surface, they also cause small changes in the local gravity. Earthquakes under oceans, as in the 2011 Japanese quake, can also change the shape of the sea bed. This displaces water and changes the sea level, which in turn also affects gravity.
After more than doubling its planned life in orbit, the satellite recently ran out of fuel and re-entered the atmosphere, largely disintegrating in the process. Although the satellite is no longer in orbit, its real mission is only just starting because scientists will be analyzing the data for years to come to help understand many aspects of our world.
Image courtesy of DGFI/TU Delft.