Back to the Drawing Board

Minutes before the 1989 World Series game was scheduled to begin, the ground shook Candlestick Park, and millions of TV viewers watched in disbelief. The San Francisco Bay Area had been rattled again -- this time, claiming 62 lives, injuring 3,757 people and causing $5 billion in damage. Four years earlier, another strong quake devastated parts of Mexico City. Some 300 buildings collapsed, and more than 10,000 people died.

These calamities have forced scientists to rethink what they know about making structures safe from earthquakes, and they're using supercomputers to more accurately gauge how earthquakes shake the Earth. The eventual goal, says Jacobo Bielak< !/researcher>, professor of civil engineering at Carnegie Mellon University, is to develop three-dimensional models for earthquake-prone areas that pinpoint within a few city blocks -- instead of several square miles -- how the Earth moves, because ground motion can vary significantly over short distances. During the 1989 Loma Prieta, Calif. quake, for instance, scientists recorded significantly different levels of shaking only 30 meters apart.

"The 1985 Mexico earthquake was the strong one," says Bielak, "that really got people to think, 'Are we doing things right?'" Using massively parallel computing (the Connection Machine, CM-2) at the Pittsb urgh Supercomputing Center, Bielak, assistant professor of civil engineering Omar Ghattas and graduate student Xiaogang Li have developed a three-dimensional model that h elps explain the devastation of earthquakes such as the one in Mexico City.

This snapshot depicts horizontal ground motion in an hypothetical basin 60 seconds after the onset of an 80-second earthquake caused by southwesterly seismic waves lasting 10 seconds. The image -- from a video made at the Pittsburgh Su percomputing Center -- shows large variations in ground motion within the basin.

The color-coded graph indicates how far a particular area moves relative to the maximum distance that rock-formation moved outside the basin after seismic waves struck it. The red-orange region in the basin's center, for instance, moved a distance 25 tim es greater than the rock formation. Positive values indicate easterly movement; negative values westerly movement.

These two images show peak vertical movement in the basin during the 80-second earthquake (left) and when that movement occurred in seconds (right). These results show that peak movements in adjoining segments occur at different times -- a hazardous condition because different sections of elongated structures may undergo peak vibrations at different times.

Researchers: Jacobo Bielak, Carnegie Mellon University; Omar Ghattas, Carnegie Mellon University
Hardware: CRAY Y-MP, CM-2 (Connection Machine)
Software: User-developed code
Keywords: Earthquake, modeling, simulation, epicenter, seismic motion, ground motion, Mexico City, seismic waves, magnitude, wave strength, Richter scale, double resonance, soil types, vibrational frequency, basin, structures.

Related Material on the Web:
The Quake Project Home Page
Projects in Scientific Computing, PSC's annual research report.

References, Acknowledgements & Credits