BACKGROUND: Scientists at Scripps Institute of Oceanography have 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, which sends that 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 that 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 (from a nuclear test, for example) 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: 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 suddenly, sending out a series of seismic waves. These fault lines are the main source of earthquakes.
The American Geophysical Union, the Incorporated Research Institutions for Seismology and the United States Geological Survey contributed to the information contained in the TV portion of this report.