Reported April 2006

BACKGROUND: Scientists at Scripps Institute of Oceanography in San Diego devised a method to use ultrasound images to provide key information about earthquake ruptures in near or real time following a large earthquake.

HOW IT WORKS: The new method uses ultrasound imaging, a medical technique that uses high frequency sound waves and their echoes. It's similar to how bats, whales and dolphins pinpoint locations, and to the basis for the SONAR technology used by submarines. Ultrasound waves not only let doctors see inside the body, they can provide information about the inside of an earthquake. The machine sends out high-frequency sound pulses, which bounce off objects and reflect back to a detector, sending the data to the machine's computer. The computer can calculate the distance between the machine and the objects by knowing the speed of sound through the earth and the time it takes for the echo to return. By measuring how the frequency of the echoes changes, scientists can also determine how fast the object is moving.

WHAT CAUSES QUAKES: An earthquake is a vibration that travels through the earth's crust. It can be caused by any number of things, including meteor impacts, underground explosions, such as from a nuclear test, or collapsing structures, such as a mine. But most naturally-occurring earthquakes are caused by the movement of the earth's tectonic plates. The earth's surface is made up of large plates that slide over the underlying layer. At the plate boundaries, plates can move apart, push together, or slide against each other.

WHOSE FAULT IS IT ANYWAY: Wherever plates meet, there will be faults at the boundaries. Faults are breaks in the earth's crust where the blocks of rock on each side are moving in different directions. There are many different kinds of faults, but in all of them, the various blocks of rock push together tightly and produce a lot of friction. If there is a large enough amount of friction the plates can become locked, increasing the pressure until the plates suddenly give way and snap forward, sending out a series of seismic waves. These fault lines are the main source of earthquakes.

The American Geophysical Union, the Incorporates Research Institutions for Seismology and the Unites States Geological Survey contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Kris Walker, Seismologist
Scripps Institute of Oceanography
University of California at San Diego
walker@ucsd.edu
858 534-0126

For more information about earth sciences:

American Geophysical Union
2000 Florida Avenue N.W.
Washington, DC 20009-1277 USA
1-800-966-2481
http://www.agu.org/

Incorporated Research Institutions for Seismology
1200 New York Ave. NW, Suite 800
Washington, DC 20005

John Taber
Education & Outreach Program Manager
(202) 682-2220
taber@iris.edu

FACTOID...

The U.S. Geological Survey reports more than 3 million earthquakes occur each year, which translates to roughly 8,000 each day, or one every 11 seconds. Most are so weak we never even notice.

THE BIG ONE...

The largest recorded earthquake in the United States ranked 9.2. It struck Prince William Sound in Alaska on Good Friday, March 28, 1964. Worldwide, the largest recorded earthquake struck Chile at a magnitude of 9.5 on May 22, 1960.