Â鶹´«Ã½

From Sidney Alford

Alberto Enriquez describes various lights seen in the sky before violent earthquakes that are believed to be caused by seismic movements producing extreme compression of the underlying rock (5 July, p 26).

Three years ago, in the Chocolate Mountains area of southern California, I detonated a series of 19 piles of explosive, each of about 225 kilograms. These were separated from each other by a distance of about 300 metres and triggered sequentially at intervals of about a second. The naked eye observed nothing remarkable.

Subsequent examination of a “movie” of the event, recorded on my digital camera, revealed, immediately above the flashes generated by three of the charges, a quite separate white flash in the air. Two of these were very distinct, intense, elongate emissions, an estimated 100 metres high. The third was about twice as high but less distinct. In addition, two vertical flashes appeared closer to the ground in synchrony with two other explosions, above points some hundreds of metres from the charges themselves.

Would any seismologists with access to appropriate monitoring equipment be interested in attempting to record this phenomenon?

Corsham, Wiltshire, UK