Reported February 2009

WHAT CAUSES EARTHQUAKES? An earthquake is the result of a sudden release of stored energy in the Earth's crust triggered by shifting tectonic plates. The Earth's lithosphere is an elaborate network of interconnected plates that move constantly -- far too slow for us to be aware of them, but moving, nonetheless. Occasionally, they lock up at the boundaries, and this creates frictional stress. When that gets to be too large a strain, the rocks give way and break and slide along fault lines. This can give rise to a violent displacement of the Earth's crust, which we feel as vibrations or tremors as the pent-up energy is released. However, only 10 percent or so of the total energy is released in the seismic waves. The rest is converted into heat used to crush and deform rock or released as friction.

FAULTS AND NANOCOATINGS: Earthquakes are most common along fault lines. The most famous fault is the San Andreas Fault in California which marks the plate boundary between the Pacific oceanic plate and the North American continental plate. It is more than 650 miles long. There are many different kinds of faults, but all of them involve different plates of rock pushing tightly together and creating friction as they move. The nanocoatings recently found by geologists are changing how they understand the behavior of faults. These slick nanocoatings, fractions of a millimeter thick, have been found at fault boundaries, where they can make it weaker and more susceptible to movement.

The American Geophysical Union, the Incorporated Research Institutions for Seismology, and the Materials Research Society contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Ben A. van der Pluijm , PhD
Professor of Geology
University of Michigan
Ann Arbor, MI 48109-1005
(734) 763-0373
vdpluijm@umich.edu

Incorporated Research Institutions for
Seismology
Washington, DC 20005
John Taber
Education & Outreach Program Manager
(202) 682-2220
taber@iris.edu

Peter Weiss
American Geophysical Union
Washington, DC 20009-1277
(800) 966-2481
pweiss@agu.org

Materials Research Society
Warrendale, PA 15086-7573n
(724) 779-3003
webmaster@mrs.org

ON THE WEB...