EARTHQUAKE STORY AND VALENCE FLUCTUATIONS ON THE OXYGEN SUBLATTICE

Prominent seismologists proclaim that earthquakes cannot be predicted, and almost everybody believes them. Unpredictability, however, cannot be the whole story.

While stresses build up deep in Earth's crust prior to major earthquakes, many processes take place in the stressed rocks long before catastrophic rupture. These processes are silent: they do not produce seismic signals. Instead they activate electronic charge carriers, which reside in the oxygen sublattice of minerals. Known as posi-tive holes, these charge carriers pre-exist in the matrix of minerals in the form of positive-hole pairs, chemically equivalent to peroxy links.

As rocks are stressed and dislocations start to move, the peroxy links break up, generating electron-hole pairs. Flowing out of the stressed rocks, positive holes spread into unstressed rocks, generating different types of signals-pre-earthquake signals. The challenge is to recognize these pre-earthquake signals (which are often subtle and fleeting) and to use them to build an earth¬quake early warning system.

Speaker: Dr. Friedemann Freund, NASA Ames Research Center/SETI Institute/San Jose State University

Dr. Freund has a background in crystallography and solid-state chemistry. After nearly 20 years as professor of geoscience in Germany, he came to the NASA Ames Research Center in 1985 to work on questions related to the origin of life. Out of this work came the discovery of positive-hole charge carriers, which led to his interest in earthquakes and other geophysical processes. He is affiliated with the NASA Ames Earth Science Division, a principal investi¬gator at the SETI Institute, and adjunct professor in the Physics Department at San Jose State University (see https://sites.google.com/site/friedemannfreund/).