GOCE : A seismometer in orbit around the Earth
Most people think that seismometers are ground-based instruments, but today earthquakes can also be detected by satellites. Researchers of the Institut de Recherche en Astrophysique et Planétologie (IRAP-OMP, UPS, CNRS) in collaboration with the CNES, the IPGP and the University of Delft, demonstrated it using data from the GOCE mission (Gravity and Ocean Circulation Explorer) of the European Space Agency (ESA).
Right panel: Propagation of seismic waves at the surface of the Earth under the orbit of GOCE (Modified from ESA AOES Medialab (2008))
The GOCE satellite, called "the first seismometer in orbit around the Earth," was able to detect sound waves at very low frequencies generated in the atmosphere by the devastating earthquake of Tohoku in Japan (March 11, 2011). Indeed, the ground vibrations during an earthquake produce acoustic waves which propagate vertically in the atmosphere. Using the very accurate measurements of the vertical acceleration of the GOCE satellite, which orbits the Earth at an altitude of about 270 kilometers, and deducting changes in the atmospheric density encountered by the satellite, the scientists were able to perform the first measurement "in situ" of the post-seismic infrasounds. These measurements were acquired both when the satellite crosses the wavefront over the Pacific Ocean and when it doubles it, half an hour later over Europe. The atmospheric seismic waves could be distinguished from the atmospheric gravity waves since the ratio between the vertical acceleration of the satellite and the disturbance of the air density is higher for these waves than for the gravity waves usually generated by the dynamics of the atmosphere.
In order to compare their model to the data collected, the researchers also modeled the atmospheric waves generated by the Tohoku earthquake. The comparison between these modelizations and the propagation time, amplitude and form of the waves observed by GOCE shows a good agreement. In addition, the arrival time differences between models and observations are attributed to lateral variations of the seismic wave velocities, both in the solid Earth and in the atmosphere.
The authors believe that this new satellite observable has a great potential for the study of atmospheric waves generated by tectonic activity, and synergies with the study of the dynamics of the upper atmosphere.
: Geophysical Research Letters, doi:10.1002/grl.50205, 2013
: Raphael Garcia, IRAP-OMP, mail: firstname.lastname@example.org
Press release in Nature : http://www.nature.com/news/earthquake-detected-from-space-1.12545
Press Release in ArsTechnica : http://arstechnica.com/science/2013/02/earthquakes-booms-big-enough-to-be-detected-from-orbit/