Hi EQF. Friedemann Freund, a scientist at NASA Ames, in California's Silicon Valley gave a talk about signals coming from the earth just before some major quakes during the 2001 American Geophysical Union (AGU) fall meeting.

Freund has been investigating how rocks respond to stress. "If the stress level is high, electronic charges appear that momentarily turn the insulating rock into a semiconductor," he said. Semiconductors are materials that have a level of electrical conductivity between that of a metal and an insulator, and they are used to make transistors.

"These charges are not easy to pin down. They move with impressive speed, as fast as 300 meters (1,000 ft.) per second," he said. By measuring the semiconductor properties of the rocks, Freund was able to show that the charges are positive. "Normally, these charges are dormant," he said. "But when rocks are squeezed, the charges wake up and flow out of the rock volume in which they were generated." Take Care…Don in creepy town

• NASA Ames Research