Two powerful earthquakes shook Southern California in back-to-back days last week, stoking fear among residents that a major earthquake isn’t far off. Jerome F. Hajjar, a professor of civil and environmental engineering at Northeastern, says it’s not a matter of if California will experience a huge, devastating earthquake, but when. And only some of the buildings in the state are prepared to withstand such a quake, he says.
On July 4, a magnitude 6.4 earthquake hit near the Mojave Desert, just 11 miles east of the city of Ridgecrest, California. The next day, a magnitude 7.1 earthquake hit just north of the city. The second left a crack in the earth so big that it could be seen from space. Seismologists say that an even bigger earthquake, dubbed “the Big One,” could unleash as much as 30 times more seismic energy than the earth-cracking 7.1-magnitude earthquake when it hits. They just don’t know when it will happen.
For structural engineers like Hajjar, who studies earthquake engineering in particular, “the Big One” is a constant presence on their minds.
“Not only is it constantly on our minds, it remains one of the forefront issues about which we’re aggressively doing research to improve building codes,” says Hajjar, who is the CDM Smith Professor and chair of the department of Civil and Environmental Engineering at Northeastern.
And while cities like San Francisco and Los Angeles have improved their building codes to include more rigorous protections against earthquakes, there are plenty of older buildings in both cities that are vulnerable to almost-certain destruction when “the Big One” hits, Hajjar says.
Hajjar says city officials have made important changes since the fatal 6.9-magnitude Loma Prieta earthquake struck San Francisco in 1989; they have upgraded bridges and municipal buildings such as schools to be more resilient to damage.
Hajjar and civil engineers like him are working to update building codes across the nation to improve the ability of buildings to withstand natural disasters. They’re including descriptions of new structural systems, such as those designed to absorb seismic activity better, as well as requiring architects and engineers to show more proof that their designs are resilient to disaster.
“The newer buildings are certainly in much better shape,” Hajjar says. “Older, shorter, multi-story buildings, however, tend to be relatively stiff, and they’re the most vulnerable.”
Newer buildings, Hajjar says, should be able to withstand earthquakes with magnitudes of 7.0 to 7.5. Some of the older, more brittle buildings will sustain “significant damage” at a 6.5-magnitude earthquake, and would likely collapse at 7.5.
Hajjar says that new efforts to retrofit old buildings to make them more resilient to damage could help prevent major destruction when, not if, the Big One hits..
“The Big One is going to happen,” Hajjar says, “there’s no doubt about it.”