BACKGROUND: Engineers at the University of Buffalo are launching a series of unprecedented seismic tests on a full-scale wood frame townhouse (see video on the University of Buffalo's Web site). The 73,000-pound, 1,800-square-foot structure will be the largest wooden structure to undergo seismic testing on a shake table in the United States. The townhouse is equipped with 250 sensors that will provide detailed information about how each nook and cranny behaves during five simulated earthquakes of escalating severity. A dozen video cameras will record the damage as it occurs. The tests will help engineers give people tips on keeping their homes protected during an earthquake, and will lead to larger, taller wooden structures being safely built in seismic regions nearby.
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 friction. With enough 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.
WHAT IS ELASTICITY? Different materials can withstand different amounts of deformation, a property known as elasticity. Most materials are elastic to some degree: When they are deformed or bent by an infusion of incoming energy, they will bounce back to their original shape. But elastic materials all have their limits. Metal springs and rubber bands are very elastic. Plaster and glass are not very elastic; instead, they are brittle and snap with even a small deformation.
The American Society of Civil Engineers and the Incorporated Research Institutions for Seismology, Inc. contributed to the information contained in the TV portion of this report.