SAN FRANCISCO -- Scientists on Tuesday unveiled what they described as the most detailed computer simulations depicting how hard and for how long the ground shook during the catastrophic 1906 San Francisco earthquake.

The virtual models use three-dimensional geologic maps constructed by the U.S. Geological Survey last year to recreate a comprehensive portrait of the strong ground motions.

"It's so incredibly exciting to see these waves sweeping across," said seismologist Mary Lou Zoback of the USGS in Menlo Park.

The computer models should aid engineers determine which buildings are most at risk during severe ground shaking and help emergency planners with their disaster preparedness, scientists said.

On April 18, 1906, a magnitude-7.8 quake struck San Francisco, sparking fires that killed about 700 people and leveled most of the city.

The temblor was centered about 2 miles offshore of San Francisco and ultimately caused shaking and damage along a 300-mile stretch of the San Andreas Fault.

The new simulations reveal how fast the seismic waves propagated from the epicenter, racing at 8,000 mph, Zoback said.

The models show strong jolting was felt at San Francisco City Hall about three seconds after the ground ruptured. Thirty seconds after the quake struck, the entire San Francisco Bay region experienced intense jerky motions.

Scientists said they will apply the same methods to study the Hayward Fault, which last ruptured in 1868. Scientists say there is a one-in-four chance that a quake greater than magnitude-6.7 will hit the fault between 2002 and 2032.