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Subject: A seismometer in orbit around Earth
From: George Bush ke6pxp@.......
Date: Tue, 12 Mar 2013 10:06:57 -0700



A friend sent this interesting article:

>>A seismometer in orbit around Earth
>>
>>Most people think of seismometers as=20
>>ground-based instruments, but earthquakes
>>can be detected by satellites too, as=20
>>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=20
>>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=20
>>using the precise vertical acceleration
>>measurements of the GOCE satellite, which orbits Earth in the thermosphere=
 at
>>about 270 kilometers (about 170 miles)=20
>>altitude, as well as deducing air density
>>variations encountered by the satellite, the=20
>>scientists can detect these waves. The
>>earthquake-generated atmospheric waves can be=20
>>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=20
>>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=20
>>synthetic data were ascribed to lateral
>>variations of both seismic velocities in the=20
>>solid Earth and sound speed in the
>>atmosphere. The study highlights the potential for future satellite-based
>>observations of earthquakes.
>>
>>Source:
>>Geophysical Research Letters, doi:10.1002/grl.50205, 2013
>>http://onli=
nelibrary.wiley.com/doi/10.1002/grl.50205/abstract
>>
>>Title:
>>GOCE: the first seismometer in orbit around the Earth
>>
>>Authors:
>>Raphael F. Garcia: Universit=E9 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 Lognonn=E9: Equipe G=E9ophysique Spatiale et Plan=E9taire,=
 Institut de
>>Physique du Globe, Sorbonne Paris Cit=E9, Univ Paris Diderot, UMR 7154=
 CNRS,
>>Saint Maur des Foss=E9s, France;
>>
>>Eelco Doornbos: Faculty of Aerospace=20
>>Engineering, TU Delft, Delft, Netherlands;
>>
>>Florian Cachoux: Universit=E9 de Toulouse; UPS-OMP; IRAP; Toulouse, France
>>and EOST, Strasbourg, France.
>>
>>George



A friend sent this interesting article:

A seismometer in orbit around Earth

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.

Source: 
Geophysical Research Letters, doi:10.1002/grl.50205, 2013
http://onlinelibrary.wiley.com/doi/10.1002/grl.50205/abstract

Title:
GOCE: the first seismometer in orbit around the Earth

Authors:
Raphael F. Garcia: Universit=E9 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 Lognonn=E9: Equipe G=E9ophysique Spatiale et Plan=E9taire, Institut de
Physique du Globe, Sorbonne Paris Cit=E9, Univ Paris Diderot, UMR 7154 CNRS,
Saint Maur des Foss=E9s, France;
 
Eelco Doornbos: Faculty of Aerospace Engineering, TU Delft, Delft, Netherlands;
 
Florian Cachoux: Universit=E9 de Toulouse; UPS-OMP; IRAP; Toulouse, France
and EOST, Strasbourg, France.

George

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