Tikalon Blog by Dev Gualtieri

Earthquake Prediction

January 16, 2013

There was a magnitude 7.5 earthquake on January 5, 2013, about 94 kilometers west of Craig, Alaska .[1] Fortunately, it caused no damage, and there were no deaths. Although large magnitude earthquakes like this are infrequent, their personal and economic consequences can be huge, as the 2011 Tohoku earthquake and concurrent tsunami have shown.

No place is really free from earthquakes. On February 2, 2009, a magnitude 3.0 earthquake occurred with an epicenter just seven miles from my house, located in a generally earthquake-free region of Northern New Jersey .[2]

Epicenter (largest circle) and aftershocks of the January 5, 2013, earthquake off the coast of Alaska.

In this chart, the quake magnitude is represented by the circle diameter.

(USGS image).

I wrote about earthquake prediction in two previous articles (Earthquake Prediction, February 18, 2011 and Earthquake Warning, March 27, 2012 ). Although humans have become increasingly able to predict the weather , we're far from being able to predict earthquakes.

It's interesting that animals appear to be better at earthquake prediction than humans. Such a trait would offer an evolutionary advantage , so it might have been perfected by natural selection . Some birds and bacteria have been found to have magnetic receptors , so that might be one possible mechanism. Animals may also respond to changes in electric field strength. There are many anecdotes about animal prediction of earthquakes.

One such anecdote was told by Claudius Aelianus , a Roman author who lived around 300 AD . Aelianus wrote in Greek , although he is mostly known through the many Latin translations of his works. One of his popular works, Varia Historia (ποικιλη 'Ιστορια, "Various History") is best known for its exposition of fly fishing . It mentions the use of lures constructed from wool and feathers .

De Natura Animalium (Περι Ζωων 'Ιδιοτητος, "On the Characteristics of Animals") by Aelianus contains a description of the destruction in 373 BC of the Greek city of Helike by an earthquake and tsunami. The description of the event, in Book X1, Chapter XIX,[3] is shown in the figure. My translation (up to "et pariter cum urbe...") is as follows:

When a house falls to ruin, this is foreseen by the mice and weasels who are there, and they quickly leave. They say that this happened in Helice. For wicked things befell the Helice people in Ionia, and their divination through sacrifices on the altar, like those in Homer, foretold these. Five days before Helike disappeared, all the mice, weasels, snakes, centipedes and beetles, and all other such creatures, left en masse by the road that leads to Coria. The people of Helice saw these things as they happened, and they were awestruck, not knowing the cause or even guessing the reason. However, soon after these creatures had departed, an earthquake occurred in the night, the city subsided, and it was destroyed by a flood of water.

Changing water level in wells was also seen in antiquity as an earthquake precursor . Other possible detection techniques have appeared in our technological age, including

• Radon dissolved in well water.
• Changes in electrical noise caused by the piezoelectric effect in rock under stress.
• Fractoluminescence , in which the electric fields caused by separation of mineral crystal planes will generate light.
• High intensity ultralow frequency (ULF) radio signals .
• Satellite remote sensing of electromagnetic fields .

ULF signals as a possible precursor for earthquakes was an accidental discovery by Antony Fraser-Smith , an electrical engineer at Stanford University , and his graduate student . They were studying ULF radio waves in the frequency range of 0.01 to 10 hertz produced when the solar wind interacts with Earth's magnetosphere .[4]

Twelve days before the Loma Prieta earthquake of 1989 , Fraser-Smith and Arman Bernardi, his student, recorded a high intensity ULF signal; and then, three hours before the earthquake, there was a ULF signal 20-30 times larger than the typical signal level.[4] ULF precursors to earthquakes have been detected by satellites.[5-8] ULF signals can penetrate tens of miles into the Earth with little loss.

Geophysicists are looking at other electrical signals closer to the ground. One poster[9] presented at the 2012 Fall Meeting of the American Geophysical Union (December 3-7, 2012, San Francisco ) describes a multisensor approach focused primarily on the magnetic fields produced by electrical discharges within the Earth. As described online by National Geographic , Stellar Solutions (Cambridge, Massachusetts ) is working on a QuakeFinder project.[10] A magnitude six earthquake seems to produce an electrical current of about 100,000 amperes, and a magnitude seven earthquake will produce about double that.[10]

As Faraday found, where there's electrical current, there's also a magnetic field, so the QuakeFinder has been placing magnetometers along faultlines in California , and in other countries. These magnetometers can detect such electrical discharges at 16 kilometer (10 mile) depths. These detect a background signal of about ten pulses per day, but this rate increases to more than a hundred per day two weeks before a major earthquake; then, there's a period before the quake when the rate is reduced to the background level.[10]

Since there's a problem with false signals caused by surface effects, other sensors are deployed to sort things out. The QuakeFinder team has been building a statistical database, and they've reached the point at which they think they can make forecasts.[10] They would be wise to avoid making predictions in Italy .[11]

Earthquake Prediction

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