Chances of really ‘Big One’ in California have increased

The odds have just gone up that a major earthquake – we’re talking magnitude 8 – will strike California in the next three decades.

The U.S. Geological Survey has updated its quake risk assessment for California. The federal agency now says there’s a 7 percent chance that California will be hit with a magnitude 8 earthquake in the next 30 years, up from 4.7 percent.

A magnitude 8 earthquake would be nearly 90 times more powerful than the magnitude 6.7 Northridge earthquake in 1994. It’s no exaggeration to say that a quake that big in a populated area would have devastating effects.

The Geological Survey says its new finding result from the work of scientists looking at data from hundreds of fault segments in the

San Andreas system, which stretches from the Mexican border to Humboldt County. One reason for the increased risk is that geologists are learning more about the

interconnectivity of faults. They took into consideration the prospect that two faults could rupture at the same time.

The USGS says smaller, but still dangerous temblors are a near certainty in California over the next three decades. In Southern California, the chance of a Northridge-size quake in the next 30 years is 93 percent. In Northern California, it’s 95 percent.

Coincidentally, Los Angeles Mayor Eric Garcetti is pushing a 30-year plan that would require property owners to strengthen thousands of vulnerable buildings in the city. Details of that plan are still being worked out and it’s not clear if owners will get public subsidies for retrofitting.

The U.S. Geological Survey report is a forecast, not a prediction. Experts still don’t know exactly where or when a quake will hit.