California quake is overdue, but is that where we should be looking?

The National Earthquake Conference has issued a warning about a quake along the southern San Andreas fault. But with California more prepared than ever, should our focus lie elsewhere?

Noah Berger/AP/File
A skateboarder in Napa, Calif. launches himself off a sidewalk buckled by a 2014 earthquake. A leading seismologist suggested this week that the San Andreas fault in southern California is overdue for a major quake.

California should be bracing for another major earthquake, according to a leading seismologist at the quadrennial National Earthquake Conference in Long Beach this week.

Sitting astride the nation's most famous fault line – the San Andreas, one of the best understood and most extensively studied faults in the world – southern California does indeed seem ripe for a major earthquake.

"The springs on the San Andreas system have been wound very, very tight," Thomas Jordan, director of the Southern California Earthquake Center, said in the opening keynote speech. "And the southern San Andreas fault, in particular, looks like it's locked, loaded and ready to go."

The last major quake to hit the area – a 7.9 on on the Richter scale – occurred in 1857. In the intervening decades, steps have been taken to mitigate the impact of these natural hazards. Some observers now suggest that there are other parts of the country more at risk and less well prepared.

After a series of relatively minor earthquakes in the latter half of the twentieth century, major changes to California building codes were implemented to provide protection going forward.

The city of Los Angeles, in particular, has taken steps to create an earthquake-resistant environment. Just last year, the city, passed a law requiring the retrofitting of historic buildings to reduce their vulnerability.

"Today, Los Angeles makes good on our promise to take action before it's too late," Mayor Eric Garcetti said in a statement last fall. "Together, we're leading the nation in requiring this level of building safety retrofit before, not after, the big quake we know is coming."

The legal requirements followed a report by the mayor's office, headed by a seismologist and US Geological Survey science advisor, and they garnered praise from both the American Society of Civil Engineers – which described them as "the nation's strictest seismic retrofit mandate" – and the Structural Engineers Association of Southern California (SEAOSC).

"Any government retrofit mandate must give careful consideration to costs associated with construction and interruption," read an SEAOSC statement, "but we believe these cost considerations should not be allowed to outweigh the importance of public life-safety, personal and community resilience, and continued regional economic viability after the next major earthquake."

Yet there is an inherent lack of predictability surrounding earthquakes, as the inhabitants of Japan discovered in 2011, when the magnitude 9.0 event devastated the country's northeast and obliterated previous assumptions that nothing stronger than an earthquake of magnitude 8.4 would ever strike that region.

Some analysts would draw the attention of those in the West Coast earthquake preparation business a little further north, to a fault line whose existence only came to light 45 years ago: the Cascadia subduction zone, arcing through the ocean floor for 700 miles, just off the coast of the Pacific Northwest.

Seismologists believe that this fault line has the capacity to produce an earthquake far in excess of anything San Andreas might be storing up, as Kathryn Schulz explained in The New Yorker, but the hope is that such an event restrains itself for many centuries to come.

"This is one time that I'm hoping all the science is wrong, and it won't happen for another thousand years," Kenneth Murphy, who directs the Federal Emergency Management Agency's Region X, responsible for Oregon, Washington, Idaho, and Alaska, told Ms. Schulz.

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