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Japan quake struck Earth’s ionosphere first

Magnitudes of recent earthquakes

The devastating earthquake that struck Japan this year may have rattled the highest layer of the atmosphere even before it shook the Earth, a discovery that one day could be used to provide warnings of giant quakes, scientists find.

The magnitude 9.0 quake that struck off the coast of Tohoku in Japan in March ushered in what might be the world’s first complex megadisaster as it unleashed a catastrophic tsunami and set off microquakes and tremors around the globe.

Scientists recently found the surface motions and tsunamis this earthquake generated also triggered waves in the sky. These waves reached all the way to the ionosphere, one of the highest layers of the Earth’s atmosphere.

 

 

Now geodesist and geophysicist Kosuke Heki at Hokkaido University in Japan reports the Tohoku quake also may have generated ripples in the ionosphere before the quake struck.

Disruptions of the electrically charged particles in the ionosphere lead to anomalies in radio signals between global positioning system satellites and ground receivers, data that scientists can measure.

Heki analyzed data from more than 1,000 GPS receivers in Japan. He discovered a rise of approximately 8 percent in the total electron content in the ionosphere above the area hit by the earthquake about 40 minutes before the temblor. This increase was greatest about the epicenter and diminished with distance away from it.

“Before finding this phenomenon, I did not think earthquakes could be predicted at all,” Heki told OurAmazingPlanet. “Now I think large earthquakes are predictable.”

Analysis of GPS records from the magnitude 8.8 Chile earthquake in 2010 revealed a similar pattern, Heki said. These anomalies also may have occurred with the Sumatra magnitude 9.2 earthquake in 2004 and the magnitude 8.3 Hokkaido earthquake in 1994, he added.

If true, further research could lead to a new type of early-warning system for giant earthquakes.

The anomaly is currently seen before earthquakes only with magnitudes of about 8.5 or larger, Heki cautioned. Still, if researchers can detect what specifically causes this ionospheric phenomenon, it also might be possible to detect precursory phenomena for smaller earthquakes, he said.

Heki did caution that the ionosphere is highly variable — for instance, solar storms can trigger large changes in total electron content there. Before researchers could develop an early-warning system for earthquakes based on ionospheric anomalies, they would have to rule out non-earthquake causes.

Heki detailed his findings online Sept. 15 in the journal Geophysical Research Letters.

This story was provided by OurAmazingPlanet, sister site to LiveScience.

Atmosphere Above Japan Heated Rapidly Before M9 Earthquake

Technology Review

Infrared emissions above the epicenter increased dramatically in the days before the devastating earthquake in Japan, say scientists.

Geologists have long puzzled over anecdotal reports of strange atmospheric phenomena in the days before big earthquakes. But good data to back up these stories has been hard to come by.

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.

Ref: arxiv.org/abs/1105.2841: Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary Results.