Do Earthquakes Telegraph Their Punches?
On May 16, 1960, radio astronomer James Warwick of the University of Colorado noted a strange signal recorded at widely separated receivers in Michigan, Colorado, New Mexico and Hawaii. Charts of the signal were similar at all the sites, and astronomers concluded that the source was not extra-terrestrial, but that it must surround the earth or hang over it like a cloud. At any rate, they knew that it was large in extent and not just a point source.
Six days later, on May 22, one of the largest earthquakes in recorded history struck Chile. This magnitude 8.9 earthquake was accompanied by fault breakage along a line 540 miles (900 km) long.
Twenty-odd years later, the same astronomers who made the original observations have now concluded that the radio signals they recorded in 1960 were likely due to stress-induced microfracturing in quartz-bearing rocks of the Chilean epicentral zone.
Some minerals, notably quartz, are piezoelectric--that is, they produce electricity when subjected to pressure or stress. This same phenomenon is probably also responsible for "earthquake lights," the luminescence sometimes reported (and, on occasion, photographed) in the sky during earthquakes. Freely propagating electromagnetic radiation arising from microscopic rock fractures in quartz-bearing rocks such as granite could also give rise to radio waves in the frequency band at which the radio astronomy receivers were operating in 1960. Laboratory tests by Warwick and other scientists have demonstrated that this can be produced in a controlled environment.
If the correlation actually does exists in nature--that is, if radio wave emissions can be detected from a stressed earthquake volume before an earthquake actually occurs--it could have immense potential for actual prediction.
However, a single example does not a theory make, as Warwick is quick to point out. For example, the anomalous radio signal in 1960 lasted for 20 minutes, six days before the earthquake. What would be the significance of the relative time spans? Also, even though the scientists were aware that it was happening, they were unable to identify the source area. In subsequent years, it has been found that the possibilities could have been narrowed down if the workers had known what they were looking for, but at the time, they were looking in the wrong direction.
The single factor which makes it seem unlikely that this will ever be a workable approach to earthquake prediction is that the Chilean earthquake is the only one with which such electromagnetic emission has been linked.
The great Alaska earthquake of March 28, 1964, was of comparable size (magnitude 8.5) as the Chilean earthquake, but no radio signal whatsoever has been identified which may have been related to it.
There may be a reasonable explanation for this. A considerable portion of the Chilean fault was exposed to the air, rendering more plausible the escape and propagation of fracture radiation. The principal fracture associated with the 1964 Alaska earthquake extended from Prince William Sound southwestward for some 400 miles (700 km) past Kodiak Island. Practically all of this path lies beneath the ocean, which would effectively block the transmittal of electromagnetic radiation from the stressed earthquake volume.
In fact, the same thing may be said about many of the earth's seismically active areas. Most earthquakes occur where oceanic and continental "plates" meet, and very often the major earthquakes of the world occur just offshore.
