What Southern California Learned From Mexico’s Earthquake

Last week’s devastating earthquake in Mexico City provides a glimpse into some of the worst case scenarios that could befall California in the event a similarly catastrophic tremor. In particular, some experts are now looking at the damage to buildings in and around the epicenter to see which ones sustained the most damage, which ones survived, and which completely crumbled.

To the amateur observer, the results yield some big surprises.

In Tuesday’s quake in Mexico, preliminary reports suggest that shorter buildings were especially susceptible to collapse, including older structures that had survived the nation’s 1985 magnitude 8 earthquake that killed an estimated 10,000 people. Meanwhile, unlike the ’85 quake, Mexico City’s taller buildings appeared to ride out the latest temblor in better shape.

Seismology and engineering experts say because Tuesday’s calamity hit far closer to Mexico’s capital — 80 miles away compared with 250 miles in the 1985 quake — shorter buildings were far more vulnerable than they were during the earthquake that struck a generation ago.

The reports illustrate a fact of seismology: Short buildings are especially at risk when big earthquakes strike nearby. They actually can avoid major damage if the structures are farther away from the origin of megaquakes.

Taller buildings, meanwhile, are especially threatened by megaquakes, even if the temblors originate from a significant distance.

Experts say the lessons are clear for California and underscore an ominous warning: Just because your home or workplace survived a previous earthquake doesn’t mean it will endure the next one.

According to a 2008 U.S. Geological Survey simulation, at least five high-rise buildings in Southern California could completely collapse during a 7.9 magnitude earthquake along the San Andreas. But the problem could be even worse; we don’t know because so many buildings simply have not been tested.

“We don’t really know what’s going to happen to those really tall buildings. We’ve never put them through a really big earthquake,” Jones said.

Downtown L.A.’s shortest buildings also haven’t been tested with extreme shaking, Jones said. At no point in modern history has downtown Los Angeles endured the kind of intense shaking that the San Fernando Valley did during the 1994 Northridge earthquake.

“Even Santa Monica” has not, she said, despite the intensity of damage in that coastal city during the ’94 quake, Jones said. “The reason there was so much damage there was because of how old the buildings are.”

We do know some basic but important facts about which buildings are the most and least likely to withstand a major earthquake. And if you’re worried about your own, you can type the address into a database here to find out.  

In short, we’re looking at the brick buildings and brittle concrete structures with weak first floors, said Kit Miyamoto, a member of the California Seismic Safety Commission and chief executive officer of Miyamoto International, a global structural engineering firm. There an estimated 1,500 in Los Angeles alone. In the event of a major earthquake, they’re deathtraps. But owners have more than 20 years to retrofit them.

That’s probably not good enough.

“We should go faster,” Miyamoto said. “The earthquake will not wait for us.” 



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