California has ‘been quiet for a while,’ but threat of a catastrophic earthquake is real
This week’s catastrophic earthquake in Turkey and Syria is just the latest warning of the potential risks for California and other seismically active areas.
Some California cities have retrofitted or demolished problem buildings following quakes in the 1980s and 1990s. But many buildings in the state have not endured the same kind of intense shaking experienced in Turkey and Syria.
The magnitude 7.8 earthquake struck southeastern Turkey at 4:17 a.m. local time Monday on the East Anatolian fault. Aftershocks have rippled throughout the southeast part of the country and Syria. A powerful magnitude 7.5 aftershock on a different fault struck nine hours later, with an epicenter 60 miles to the northeast, producing another round of devastation.
The San Andreas fault is capable of similar activity.
“We’ve had 7.8 earthquakes in our historic past. We’ve had a great run without them, but it’s important to be prepared for these possibilities in the future,” said U.S. Geological Survey research geophysicist Kate Scharer.
Two of those have occurred on the San Andreas: the 1906 earthquake that destroyed much of San Francisco and the 1857 quake that ruptured a length of the fault from Monterey County through Los Angeles County and into the Cajon Pass.
“There will be 7.8s in our future. Absolutely. We have the faults, we’ve seen it in the past, it will happen again,” said seismologist Lucy Jones, a research associate at Caltech. “The timing of them, as far as we can tell, is random. And there’s no way to say when it’s going to be happening. … Compared to the longterm average, we’ve been quiet for a while.”
The scale of the building collapses in Turkey and Syria, some captured on video, could be attributed to a number of factors. Some of the structures may have been built before the advent of modern building codes. The collapses could also be due to corruption in safety inspections or incompetence in design practices — issues that have come up in Mexico, Taiwan and New Zealand.
But structural engineers have said that a big quake in California would also be devastating, if not on the same scale. They have long warned about the risk of brittle, concrete buildings collapsing, as occurred during the 1971 Sylmar and 1994 Northridge quakes. When the concrete Veterans Administration Hospital in San Fernando pancaked in the 1971 earthquake, 49 people were killed.
Minimum construction requirements were strengthened in the years after the Sylmar quake, but those rules affected only new construction. More concrete buildings suffered significant damage in the 1994 Northridge quake.
David Cocke, president of the Earthquake Engineering Research Institute and a structural engineer with Gardena-based Structural Focus, said some of the collapsed buildings he has seen in news footage from Turkey appear to have been constructed from non-ductile concrete, in which inadequate steel reinforcing bars allow concrete to explode from columns when shaken.
Similar videos emerged after a magnitude 7.1 earthquake in 2017 struck Mexico. One showed a building wobbling, followed by concrete falling out of a groundfloor column; the columns then flexed, and the upper floors crashed down, sinking into a cloud of dust.
A concrete school in Mexico City that collapsed in that quake killed 19 students and seven adults.
Videos and photos from Turkey and Syria show building of various eras — some old, some modern — collapsing. But they also show that many others survived the shaking. Experts say new buildings in Turkey — when properly built to local codes — are comparable to California’s standards.