While death and taxes are said to be life’s only certainties, on Monday California scientists added another calamity to that list: earthquakes.

There is a 99.7 percent chance that a major temblor will strike the Golden State in the next 30 years, according to the first comprehensive study of the state’s earthquake risks.

“The sobering thing to me is we’ve never seen anything like a 99 percent probability before,” said Tom Parsons, a seismologist with the U.S. Geological Survey in Menlo Park. “That’s not a number we throw around a lot.”

Surprisingly, Monday’s study also found the odds of a magnitude 6.7 quake are nearly identical for Northern and Southern California. Researchers had long assumed that the southern half of the state was at significantly higher risk.

A magnitude 6.7 quake is capable of killing scores of people and causing billions of dollars in damages to homes and businesses. California has had more than a half dozen of them in the past 30 years.

The 1994 Northridge earthquake was a magnitude 6.7 and it killed more than 50 people, injured more than 7,000 and left 20,000 people homeless in Southern California. The 1989 Loma Prieta earthquake, which felled a portion of the San Francisco Bay Bridge and delayed the World Series, was not much larger – a magnitude 6.9. It resulted in 63 fatalities and $6 billion in damages.

Scientists have known for some time that a “Big One” is likely to occur here.

Five years ago, seismologists estimated the Bay Area had a 62 percent chance of experiencing a catastrophic earthquake within three decades. But Monday’s report, which was drafted by a multidisciplinary group of scientists and engineers, is the first to compare earthquake probability for Northern and Southern California.

To make their predictions, researchers combined information from several fields of earthquake science in a mathematical model.

They considered how fast points of California are moving in response to the steady motion of the Pacific and North American tectonic plates. They analyzed data gleaned from trenches dug into the faults, considering how frequently earthquakes have occurred since prehistoric times.

In the end, they determined Northern California’s probability of a sizable tremor in the next 30 years is 93 percent, while Southern California’s is estimated at 97 percent. The Bay Area and Los Angeles, they found, have nearly identical odds of having a massive quake – about two in three.

“We often think about Los Angeles being at higher probability, but this is saying, no, the probability is about the same,” said Tom Brocher, coordinator of the USGS’ Northern California earthquake hazards investigations.

Greatest threat

In the Bay Area, the greatest threat is posed by the Hayward-Rodgers Creek fault, which rests beneath the densely populated East Bay. Recent data shows the Hayward fault goes off about every 140 years – and it has been 139 years since it last did. Taking that into consideration, the scientists increased their estimate of the probability that that tectonic time bomb will go off, from 27 percent to 31 percent. A major quake on the Hayward fault would likely cause damage from San Jose to Santa Rosa, they said.

“I have earthquake insurance – I’m concerned,” said David Schwartz, an earthquake geologist with the USGS.

California’s many earthquake faults are among the most active in the United States. Scientists have been urging the public for years to get prepared, stash emergency supplies of food and water and have a family plan for after an earthquake.

Monday’s report, they said, underscores that it is not a matter of if – but when – a devastating quake will hurt the state. And they hope the public has not grown deaf to their message.

“This is another reminder,” Brocher said, “we live in earthquake country.”

Big Thanks to MercuryNews.com for this article!