The graph above displays how Japan's atmosphere heated up prior to the earthquake and subsequent Tsunami. In recent
years, however, various teams have set up atmospheric monitoring stations in
earthquake zones and a number of satellites are capable of sending back data
about the state of the upper atmosphere and the ionosphere during an
earthquake.
Last year,
we looked at some fascinating data from the DEMETER spacecraft showing a
significant increase in ultra-low frequency radio signals before the magnitude
7 Haiti earthquake in January 2010
Today,
Dimitar Ouzounov at the NASA Goddard Space Flight Centre in Maryland and a few
buddies present the data from the Great Tohoku earthquake which devastated
Japan on 11 March. Their results, although preliminary, are eye-opening.
They say
that before the M9 earthquake, the total electron content of the ionosphere
increased dramatically over the epicentre, reaching a maximum three days before
the quake struck.
At the same
time, satellite observations showed a big increase in infrared emissions from
above the epicentre, which peaked in the hours before the quake. In other
words, the atmosphere was heating up.
These kinds
of observations are consistent with an idea called the
Lithosphere-Atmosphere-Ionosphere Coupling mechanism. The thinking is that in
the days before an earthquake, the great stresses in a fault as it is about to
give cause the releases large amounts of radon.
The
radioactivity from this gas ionises the air on a large scale and this has a
number of knock on effects. Since water molecules are attracted to ions in the
air, ionisation triggers the large scale condensation of water.
But the
process of condensation also releases heat and it is this that causes infrared
emissions. “Our first results show that on March 8th a rapid increase of
emitted infrared radiation was observed from the satellite data,” say Ouzounov
and co.
These emissions
go on to effect the ionosphere and its total electron content.
It certainly
makes sense that the lithosphere, atmosphere and ionosphere are coupled in a
way that can be measured when one of them is perturbed. The question is to what
extent the new evidence backs up this idea.
The Japan
earthquake is the largest to have struck the island in modern times and will
certainly turn out to be among the best studied. If good evidence of this
relationship doesn’t emerge from this data, other opportunities will be few and
far between.
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