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Tuesday, April 15, 2008

99.7 Percent Probability That The 'Big Quake' Will Hit California

Most of us have heard, time and again, that the "Big One" was going to hit, referring the a large scale devastating earthquake that would hit California. For the first time though, experts are saying it is, indeed, a certainty.
According to calculations done by experts, there is a 99.7 percent probability that California will face a magnitude 6.7 quake or larger by 2037.

Despite all the talk for years, this is the first time that scientists have held this level of certainty and according to Tom Parsons, who is a seismologist with the U.S. Geological Survey in Menlo Park, "The sobering thing to me is we've never seen anything like a 99 percent probability before. That's not a number we throw around a lot."

The study is called "Uniform California Earthquake Rupture Forecast", and it took three years to complete and it was prepared in cooperation with the California Geological Survey and the Southern California Earthquake Center.

The report itself is 104 pages long (PDF) and on page number 5, under the headers of "Results of Probability Calculations", it states:

According to UCERF 2, a M ≥ 6.7 earthquake is virtually assured in California during the next 30 years (99.7% probability of occurrence). Larger events are less likely: the mean 30-year UCERF 2 estimate gives a 94% chance of a M ≥ 7.0 earthquake, a 46% chance of a M ≥ 7.5 shock, and 4.5% chance of a M ≥ 8.0 event.

(Participation probability maps, displaying the mean UCERF 2 probabilities that an individual 0.1º × 0.1º cell in the statewide grid will be involved in a fault rupture of any source type above the specified magnitude threshold during the next 30 years. The magnitude thresholds shown here are M • 5.0, 6.7, and 7.7. Probability color scale is logarithmic; i.e. each decrement unit represents a 10-fold decrease in probability.)

Even more surprising to these experts is that although it has long been assumed that the risk to the southern half of California was much higher, according to this report the odds of a magnitude 6.7 quake are nearly identical for Southern and Northern California.

The last time a quake of this magnitude rattled California was the 1994 Northridge disaster, which killed 72 people, injured more than 9,000, and caused $25 billion in damage.

California sits on 300 faults throughout the state, which sits on top of the meeting of two of Earth's major tectonic plates, the Pacific and the North American.

The stories of "the big one" all came about because with the type of seismic activity which California suffers, on average, is about 10,000 quakes a year, the majority of which are too small to even be felt, it was only a matter of time before scientists were able to ascertain a clear time line and probability of magnitude .

This latest report is the first time though that experts can say, without a doubt, not only that it will happen, but they are also capable of giving us the 99.7 percent probability that it will happen and a time frame for the near certain event.