Most of us have probably followed the ongoing story of the March earthquake and tsunami in Japan, and the dangerous situation with the nuclear power plants there. The quake, estimated at magnitude 9, was the largest to strike Japan in modern times. We’ve also seen other major earthquakes in Haiti and New Zealand. At this point, we know a good deal about the underlying structure of the tectonic plates that make up the Earth’s crust, and also about the mechanics of the faults between plates; the buildup and subsequent sudden release of stress along these faults is an underlying cause of earthquakes. We haven’t made too much headway, though, when it comes to predicting earthquakes.
The “Physics ArXiv” blog at Technology Review recently summarized some very interesting results, gathered from observations just before the Japanese earthquake. The results [abstract, full article PDF available], which are preliminary and subject to revision, were presented at the 2011 European Geosciences Union conference in Vienna.
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.
The researchers examined data on infrared radiation, measured by satellite and provided by the Climate Prediction Center at NOAA; they also looked at ionospheric observations from three sources: the GPS/TEC ionosphere maps, ionospheric tomography from satellites in low earth orbit, and data from ground stations in Japan. They discovered two interesting effects:
- Beginning on March 8 (three days prior to the earthquake), there was a rapid increase in the emitted infrared radiation, centered over the area of the quake’s epicenter.
- During the period March 3-11, there was an increase in electron density observed by all three systems, peaking on March 8.
As the Physics ArXiv post points out, this is consistent with an existing hypothesis on the interactions between events in the lithosphere and the atmosphere.
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.
Radon [Rn, atomic number 86] is a radioactive gas, and a natural product of the radioactive breakdown of uranium. It is an α-emitter; its most stable isotope, 222Rn, has a half-life of 3.8 days. It is certainly plausible that a large release of radon into the atmosphere could cause an significant increase in electron density (it is called ionizing radiation for a reason, after all). Moreover, since water molecules are electrically polar, water vapor molecules are attracted to ions in the atmosphere. This has the effect of providing nucleation sites for the condensation of water vapor to liquid water; because of water’s unusually high heat of vaporization (40.68 kJ/mol), the condensation could produce warming of the atmosphere, and hence an increase in emitted infrared radiation.
Once again, these results are preliminary, and need to be confirmed. (And it is hard to predict how soon that might happen, since getting some of that confirmation will probably require us to observe more earthquakes.) If the results hold up, they might provide a starting point for better predictions of earthquake risk. They might also help to account for the persistence of anecdotal evidence that some animals seem to sense imminent earthquakes.