Shifting grains may explain earthquake lightning

Along a fault, movement of earth could induce voltages

DENVER— Beads and flour could help explain a rare and mysterious phenomenon: lightning strikes called earthquake lights that occur before or during major quakes. New results presented March 6 at an American Physical Society meeting demonstrate that shifting granular materials, which simulate earth along a fault, can induce remarkably high electric voltages.

A few years ago, physicist Troy Shinbrot of Rutgers University in Piscataway, N.J., developed a simple experiment to determine whether earth under stress could create conditions favorable for lightning above the surface. When he tipped a container of flour, a sensor inside registered an electrical signal on the order of 100 volts (SN: 7/14/12, p. 13).

Two new experiments using glass and plastic beads strengthen the connection between the simple setup and earthquake lights. Tanks of beads were put under pressure until one section slipped relative to another, like failing slabs of earth along a fault. The voltage surged during each slip.

The effect seems similar to static electricity, but that shouldn’t build up between particles of the same material. “It’s all very curious,” Shinbrot said. “It seems to us to be new physics.”

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