A reconstruction of lights seen before the 2007 Lima earthquake. Photograph: US Navy/DigitalGlobe
by David Hambling:
Unusual lighting is often reported in the days leading up to an earthquake. It may look like normal lightning striking upwards, or take the form of glowing spheres like ball lightning.
Other earthquake lights resemble the electrical glow of St Elmo’s Fire or an aurora. Some researchers believe that this activity may help in predicting earthquakes.
The lights are elusive, and were not photographed until a Japanese quake in 1968. The exact cause is still the subject of furious academic debate. We do know though that it is electrical and may be visible as lightning and other effects.
A recent study by the Taiwanese National University showed that lightning generally became more common in the weeks preceding an earthquake.
Some researchers are focusing on the total amount of electrons, or total electron count (TEC), in Earth’s ionosphere, which changes with electrical activity.
TEC is easy to monitor because it affects GPS signals, and there is plenty of data on how it varies over time. A study by a team at Chapman University in California found a sudden rise in TEC before the Nepal quakes this year.
However, this does not mean that predicting quakes will be simple. A paper from a team at the National Institute of Geophysics and Volcanology in L’Aquila, Italy, suggests that the correlation between TEC and earthquakes is not very strong.
The researchers point out that atmospheric anomalies have never been used to predict an earthquake, and that a link has only been suggested with hindsight.
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