Most people think of seismometers as ground-based instruments, but earthquakes can be detected by satellites too, as demonstrated by Garcia et al. using data from the European Space Agency's Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission.
They call GOCE "the first seismometer in orbit around the Earth," because it was able to detect infrasonic waves in the atmosphere generated by the 2011 Tohoku earthquake.
The shaking of the ground during an earthquake produces acoustic waves that propagate vertically in the atmosphere. By using the precise vertical acceleration measurements of the GOCE satellite, which orbits Earth in the thermosphere at about 270 kilometers (about 170 miles) altitude, as well as deducing air density variations encountered by the satellite, the scientists can detect these waves.
The earthquake-generated atmospheric waves can be distinguished from other types of gravity waves in the atmosphere because the ratio of the satellite's vertical acceleration to the perturbation in air density is higher for these post-seismic waves than for usual gravity waves in the atmosphere.
The researchers also modeled these atmospheric waves generated by the Tohoku earthquake; compared the amplitude, timing, and waveshape of the modeled waves to that deduced from the GOCE data; and find the model and data agree well.
Wave travel time delays relative to synthetic data were ascribed to lateral variations of both seismic velocities in the solid Earth and sound speed in the atmosphere. The study highlights the potential for future satellite-based observations of earthquakes.
Article: GOCE: the first seismometer in orbit around the Earth, Geophysical Research Letters, doi:10.1002/grl.50205, 2013doi:10.1002/grl.50205
By Raphael F. Garcia: Université de Toulouse, UPS-OMP, IRAP, Toulouse, France and CNRS, IRAP, 14, avenue Edouard Belin, Toulouse, France; Sean Bruinsma: CNES, Dept. of Terrestrial and Planetary Geodesy, Toulouse, France; Philippe Lognonné: Equipe Géophysique Spatiale et Planétaire, Institut de Physique du Globe, Sorbonne Paris Cité, Univ Paris Diderot, UMR 7154 CNRS, Saint Maur des Fossés, France;Eelco Doornbos: Faculty of Aerospace Engineering, TU Delft, Delft, Netherlands;Florian Cachoux: Université de Toulouse; UPS-OMP; IRAP; Toulouse, France and EOST, Strasbourg, France.