Earth’s gravity altered by 2011 Japanese Tōhoku earthquake

December 4, 2013 – TOKYO – Japan’s devastating earthquake in 2011 left its mark on more than the town of Fukushima. The European Space Agency (ESA) says that it had an impact on Earth’s gravity as well. Scientists used data from ESA’s GOCE satellite to show the effects of the 9.0 earthquake that struck east of Japan’s Honshu Island on March 11, 2011. The strength of gravity varies from place to place on Earth, and earthquakes can deform our planet’s crust and cause tiny changes in local gravity. GOCE spent four years mapping out Earth’s gravity with unrivaled precision. One reason values of gravity differ on Earth is because the materials within Earth are inhomogenous and are unevenly distributed. Since earthquakes shift around rock and other material tens of miles below the surface, they cause small changes in the local gravity. Earthquakes under oceans can also change the shape of the sea bed, displacing water and changing the sea level. GOCE data is helping scientists understand how oceans transport huge quantities of heat around the planet and develop a global height reference system. Earlier this year, the satellite’s accelerometer and ion thrusters revealed GOCE had “felt” sound waves in space from the Japanese quake. Scientists from the German Geodetic Research Institute (DGFI) and from Delft University of Technology in the Netherlands analyzed the high-resolution vertical gravity gradients measured over Japan by GOCE. The team found the quake had clearly ruptured the gravity field in the area. The latest research marks the first example that GOCE was able to find changes over time. The gravity change measured by GOCE differs in size and location, compared to those predicted by standard models.

The results, published in the Journal of Geophysical Research, are consistent with coarser observations using NASA’s Grace satellite, which measures changes over time. This suggests GOCE data will be important in improving models and it will help contribute to understanding earthquakes. “Thus, we see that GOCE gravity gradients complement other types of data such as seismic, GPS and GRACE satellite gravimetry,” Martin Fuchs, from DGFI and lead author of the study, said in a statement. “We are now working in an interdisciplinary team to combine GOCE data with other information to obtain a better picture of the actual rupture in the gravity field than is currently available.” GOCE ran out of fuel earlier this year and reentered Earth’s atmosphere, largely disintegrating in the process. The satellite more than doubled its planned life in orbit, and its data will continue to be used by scientists for years to come to help understand our planet a little better. –Red Orbit