By Josh Lieberman
The controlled implosion on Saturday of a 13-story building overlooking the San Francisco Bay in Hayward, Calif., provided not only spectacle but scientific data, as some 600 seismographs monitored the implosion's impact on the nearby Hayward Fault.
The imploded Cal State-East Bay building, Warren Hall, was the most seismically unsound building in the California State University system. That's because Warren Hall sat just 2,000 feet from the Hayward Fault, a zone of seismic activity that's "increasing likely" to see a major earthquake soon. The last major Hayward Fault earthquake was 140 years ago, in 1868, and according to the U.S. Geological Survey, major Hayward earthquakes occur roughly every 140 years.
The implosion of Warren Hall, caused by 430 pounds of high explosives, created shockwaves that researchers hoped would be the equivalent to an earthquake of 2.0 magnitude. Over 600 seismographs about the size of a 16-ounce can were placed in concentric circles 1.5 miles around Warren Hall.
U.S. Geological Survey scientists used the opportunity of the Hayward implosion to learn more about the shaking that results from seismic activity, and to help map fault lines in the area. The vibrations from Warren Hall's implosion should help the scientists figure out the location of "traces," fault lines that split off from the main fault.
"We are trying to measure ground motion," said geophysicist Rufus Catchings. "When the building comes down there will be a thump that will put seismic energy into the ground."
With a 63 percent chance that a major earthquake along the Hayward Fault will occur in the San Francisco Bay Area within 30 years, Catchings said that learning as much as possible about the Hayward Fault is necessary if we want to minimize damage.
"There is a tremendous number of things we need to learn about the fault zone if we understand that then we have a pretty good idea of what will happen in a much larger earthquake," Catchings said. "This will tell us a lot about the fault zone itself, of the amplitude of seismic energy we expect from a real earthquake."
The largest quake on the Hayward Fault was the 1868 Hayward earthquake, a 7.0-magnitude quake that claimed 30 lives. It was known as the "Great San Francisco Earthquake" until the 1906 San Francisco earthquake, a 7.8-magnitude quake that destroyed 80 percent of the city and killed about 3,500 people, took the title away. The 1906 quake was caused by a rupture in the San Andreas Fault, which runs parallel to the Hayward Fault.