The research was presented Tuesday, on the 95th anniversary of the quake, which measured about 7.8 on the Richter scale, at the annual meeting of the Seismological Society of America.

The 1906 event, which triggered the devastating San Francisco fire, was responsible for killing more than 3,000 people, destroying 28,000 buildings and making about 225,000 of the city's 400,000 residents homeless.

"The 1906 earthquake is generally seen as the first large seismic event in the world that was documented with seismic, geologic and geodetic data," said George P. Mavroeidis, a doctoral candidate in the Department of Civil, Structural and Environmental Engineering in the UB School of Engineering and Applied Sciences, who presented the research.

"However, since there were no instruments in the vicinity to record the ground motions, only qualitative approaches have been applied to estimating ground motion magnitude," he said.

The UB simulations provide the first quantitative approach to estimating ground motions of the event, which ruptured 470 kilometers, or 290 miles, of the San Andreas Fault. (By contrast, the destructive 1989 Loma Prieta earthquake ruptured only about 25 miles of the fault.)

"For these kinds of large events, the recorded ground motion data are still very scarce," said Apostolos S. Papageorgiou, Ph.D., UB professor of civil, structural and environmental engineering, who co-authored the research.

"Only with quantitative estimates of ground motions developed by seismologists can engineers then take that data and use them as input to mathematical models of structures to see if the structures could withstand the shaking of earthquakes with comparable magnitudes," he explained.

The UB researchers produced ground motion "snapshots" of low-frequency displacements and velocities for an extended area covering central and northern California and for 15 selected locations in the vicinity of the earthquake, including downtown San Francisco, Oakland, the Golden Gate Bridge, Fort Bragg and San Jose.

"These 'snapshots' give you an idea of the intensity of ground motion that was experienced during the earthquake," said Mavroeidis.

According to Mavroeidis, the research was based on accurate slip models recently developed by USGS researchers.

"These slip models, which describe how much one side of the fault slipped in relation to the other, have given us the necessary input to reproduce the ground motion generated by the 1906 earthquake and to quantitatively reconstruct the long-period and velocity field experienced by central and northern California," he explained.

The research focused on long-period motions, which are ground motions that are slower and correspond with seismic waves in which there are fewer oscillations per minute.

"These large quakes release a lot of energy in the long-period range," explained Papageorgiou, "so this range is important."

At the same time, he said, certain structures, such as high-rise buildings and suspension bridges, are considered long-period structures that "are expected to suffer or to be more severely tested during large events," he explained.

The UB researchers plan to expand their models to simulate ground motions for the 1906 quake over the entire frequency range and to recreate accelerations of ground motions.

These data then will be input into engineers' models of structures to enable them to design building and bridges that can better withstand such destructive earthquakes. - By Ellen Goldbaum

[Contact: Ellen Goldbaum]

20-Apr-2001