california earthquake, california earthquake threat, california earthquake risk
AP Photo/Lenny Ignelzi
Al McMcNeill looks over the remains of his home in the Grenada Hills area of Los Angeles
following a major earthquake on Jan. 17, 1994.

Measuring California’s Earthquake Threat

January 14, 2010 05:00 PM
by James Sullivan
Images of destruction emerging from Haiti in the wake of Tuesday’s earthquake have many wondering if California is vulnerable to a comparable disaster.

Life in “Earthquake Country”

Earthquakes are a fact of life in California, so say many residents and experts. Located above the San Andreas Fault, the tectonic boundary between the Pacific and North American Plates, means the state experiences thousands of temblors each year, most of which go unnoticed. The U.S. Geological Survey’s Earthquake Hazards Program keeps a running list of earthquakes in the California-Nevada region. According to the register, 92 earthquakes occurred in California last Tuesday.

Though the majority of these events are less than 3.0 in magnitude, their frequency is a constant reminder of the unceasing tectonic activity beneath the earth’s surface.

Risk and Preparedness

According to the 2008 Uniform California Earthquake Rupture Forecast, compiled by the USGS, Southern California Earthquake Center (SCEC) and the California Geological Survey (CGS), “[T]here is a probability of more than 99% that in the next 30 years Californians will experience one or more magnitude 6.7 or greater quakes, potentially capable of causing extensive damage and loss of life. For powerful quakes of magnitude 7.5 or greater, there is a 46% chance of one or more in the next 30 years—such a quake is twice as likely to occur (37%) in the southern half of the State than in the northern half (15%).”

The report found the San Francisco Bay Area to have a 63 percent chance of experiencing a magnitude 6.7 earthquake or greater within the next 30 years, and put the Los Angeles region’s chances at 67 percent.

Is the state prepared to handle the seeming inevitability of a major earthquake?

Christopher Beam of Slate cited a lack of national building codes in Haiti as contributing to the widespread destruction caused by the Jan. 13 temblor. California’s building codes have been updated in accordance with the understood earthquake threat, but as the Southern California Earthquake Center warns, just because the state has good codes doesn’t means its residents are safe. It advises that old buildings should be assessed and retrofitted to meet updated codes—a responsibility that sits with the building’s owner.

Unlike Haiti, which was caught off guard, California residents are aware of the earthquake threat they face: The region is referred to as “Earthquake Country”. The USGS has earthquake preparedness handbooks for the Bay Area and Los Angeles/Southern California residents with information on how to prepare and what to know, along with how quakes cause damage, who is most at risk and what type of scenarios to expect.

Historical Context: California’s shaky past

Since the late ’80s, California has experienced more than 15 earthquakes of magnitude 5.5 or greater, the most destructive of these being the 1994 Northridge earthquake, and 1989’s Loma Prieta earthquake.

The last major earthquake in the state occurred in the Northridge section of Los Angeles in 1994. The magnitude 6.7 earthquake damaged freeways, killed at least 70 people and did $20 million in damage.

On the evening of Oct. 17, 1989, a 6.9 magnitude quake hit the San Francisco and Monterey Bay regions. The 10-15 second tremor left 63 dead, more than 3,700 injured and thousands homeless. It was to that point one of the most expensive natural disasters in the country’s history, and represented the largest earthquake to occur along the San Andreas Fault since the 1906 San Francisco earthquake. It also occurred during the warm-ups before game 3 of the ’89 World Series between the San Francisco Giants and the Oakland Athletics, and as such was the first earthquake to be captured on live television. Footage is available on YouTube.

The most destructive earthquake in the country’s history occurred in San Francisco, just before dawn on April 18, 1906. The magnitude 7.8 quake came in two shocks lasting a little more than a minute. Almost immediately after the quake ended, massive fires broke out and spread quickly through the city, compounding the devastation of the earthquake. Many pipes had ruptured, cutting off the water supply, and the fire chief had been critically injured in the earthquake. The firemen, aided by 2,000 federal troops, decided to dynamite some of the buildings to create firebreaks, and only ended up causing more fires. The fires lasted four days, and in that time, as National Public Radio reports, they leveled more than three-quarters of the city.

The earthquake left more than 3,000 people dead, 225,000 homeless and destroyed more than 28,000 buildings.

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