# S.O.S.! Surviving The Big Quake

June 1, 2011

Earthquake engineers and geophysicists created quakes on the computer using a 3-D simulator that lets them see how much shaking tall buildings can handle before they collapse. In addition to studying fake quakes of various magnitudes, the researchers also recreated historic earthquakes to see what would happen today. The work will help engineers design safer, quake-proof buildings, could cut down on disaster response times, and could even help consumers decide what kind of insurance they should buy.

## Science Insider

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% or so of the total energy is released in the seismic waves. However, the rest is converted into heat, used to crush and deform rock, or released as friction.

HOW DO SCIENTISTS RATE EARTHQUAKES? An earthquake's magnitude describes how much the ground moves. The scale is logarithmic, which means that when the magnitude increases by one (say from 3 to 4, or from 4 to 5) the amount of ground motion increases by ten times. That is, a magnitude 3 quake leads to ten times as much ground motion as a magnitude 2 quake, and a magnitude 2 leads to ten times as much motion as a magnitude 1. This means that a magnitude 3 is a hundred times as violent as a magnitude 1, and a hundred times less violent than a magnitude 5.

The magnitude scale also tells us just how much energy an earthquake released. For example, a magnitude 1 earthquake releases the same amount of energy as 30 pounds of TNT exploding. Although a magnitude 2 earthquake makes the ground move ten times as much as a magnitude 1, it releases 32 times as much energy -- or roughly as much as a ton of TNT. A magnitude 5 earthquake packs the punch of a moderate nuclear weapon, and a magnitude 12 quake would be enough to put a crack all the way through the center of the Earth.

The American Society of Civil Engineers and the American Geophysical Union contributed to the information contained in the TV portion of this report.

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To Go Inside This Science:

Deboarh Williams-Hedges
Caltech Media Relations
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Peter Weiss
American Geophysical Union
pweiss@agu.org
202-777-7507

The American Society of Civil Engineers
Leikny Johnson
ljohnson@asce.org
703-295-6413

AGU is a worldwide scientific community that advances, through unselfish cooperation in research, the understanding of Earth and space for the benefit of humanity.