April 1, 2006 Using ultrasound imaging, seismologists can now determine the epicenter and magnitude of an earthquake quake within 10 to 20 minutes, precisely imaging which fault ruptured and where the rupture went. The method could help save lives through early earthquake and tsunami warnings. By the end of this year, the U.S.G.S. will be using the method to analyze earthquakes anywhere in the world.
SAN DIEGO--The first few hours following a major earthquake are critical for seismologists, rescuers and people living in the quake zone. Now, researchers can estimate where a quake made its biggest impact within 30 minutes after a big earthquake.
It was a deadly quake that shook the world. Hundreds of thousands of people died. Kris Walker, a seismologist at Scripps Institution of Oceanography at the University of California, San Diego, says, "It actually took days before the true size of that earthquake was determined."
If, in the first minutes, seismologists had known how large the quake was and exactly where it occurred, they'd have recognized a powerful and widespread tsunami would soon follow. "If our technique was used and had there been adequate communication infrastructure in that area, we would have been able to save a lot of lives," Walker says.
Walker and fellow seismologist Peter Shearer have devised a method to rapidly determine how much surface shaking is generated from the epicenter of a large quake. "What we're able to learn within 10 to 20 minutes of when the earthquake started is about which fault ruptured and where the rupture went," Shearer says.
Earthquakes produce seismic waves. The first waves detected by seismic stations are called p-waves. Once the quake is detected, earth scientists can back track to find where the quake started. Shearer says, "You get a prediction like this, in gray, of the area that experienced the greatest surface shaking."
This new, faster method of sizing up earthquakes can buy important time for people in the first hour following a major earthquake.
By the end of this year, the U.S. Geological Survey in Colorado will be using the back-projection method to analyze earthquakes anywhere in the world. It could become part of a worldwide warning system.
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.