California Earthquake: Damage Predictions of ‘Big One’ Get Bigger

A new report is predicting that a repeat of San Francisco’s 1906 earthquake would damage more than 90,000 buildings and cost $150 billion to repair.

According to the report, “When the Big One Strikes Again,” prepared for the 100th Anniversary Earthquake Conference held in San Francisco in April, a repeat of the 1906 earthquake would damage as many as 10,000 commercial buildings and displace up to 250,000 households due to damaged residences. The cost to repair and replace damaged buildings would be approximately $120 billion, the report indicated.

The California earthquake of April 18, 1906, ranks as “one of the most significant earthquakes of all time,” according to the U.S. Geological Survey. “Rupturing the northernmost 296 miles of the San Andreas Fault from northwest of San Juan Bautista to the triple junction at Cape Mendocino, the earthquake confounded contemporary geologists with its large, horizontal displacements and great rupture length.”

While there was no measure of the earthquake at the time, it is estimated to have measured anywhere from magnitude 7.7 to 8.3, according to USGS. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada, producing insured losses of $235 million at the time, equivalent to $5.2 billion in 2007 dollars, according to the Insurance Information Institute.

The “Big One” report predicted that a repeat of the 1906 quake would “instantaneously” kill more than 800 people at night, or more than 1,500 people during the day; require immediate rescue of people trapped in collapsed buildings of about half of those numbers; and seriously injure about 4,000 people at night or more than 6,000 people during the day.

More than half of the deaths would result from the collapse of unreinforced masonry and other older vulnerable buildings that have yet to be strengthened, the report predicted. The dangerous structures amount to less than 5 percent of the region’s building stock; buildings built after the mid-1970s are much safer, the report said.

Nevertheless, the report forecast that more than 400,000 people would be displaced from their homes due to extensive or complete structural damage. About 7,000 commercial buildings, about 10 percent in the study region, would be forced to close temporarily or permanently due to extensive or complete structural damage.

According to the report, San Francisco would sustain the most damage — as much as $34 billion in building-related losses — followed by $28 billion in Santa Clara County, $26 billion in San Mateo County, and $15 billion in Alameda County. For comparison, building-related losses throughout Southern California totaled $20 billion in the 1994 Northridge earthquake.

“These dramatic numbers tell us what we need to do to get the Bay Area ready for a major quake,” said Chris Poland, chair of the 100th Anniversary Earthquake Conference. “We need to act now to repair or replace our most vulnerable buildings.”

“We have to invest in what is absolutely critical,” added Rich Eisner, regional administrator of the Governor’s Office of Emergency Services. “Hospitals, fire stations, operation centers and communication facilities all must be able to ride out the earthquake so the region can respond and recover.”

Although the report focused on damage to buildings, conference officials predicted subsequent individual fire ignitions would cause an additional 5 percent to 15 percent in building damage as well as additional deaths. A conflagration similar in scale to the 1906 fire is possible and would cause a much more immense loss, the report indicated.

Damage to utilities and transportation systems also would increase losses by an additional 5 percent to 15 percent. Prolonged outages would cause economic disruption costing several times that amount.

The report was prepared by a team of engineering and ground motion experts led by Charles Kircher of Charles Kircher & Associates of Mountain View, Calif. The study was commissioned by the organizers of the 100th Anniversary Earthquake Conference, Earthquake Engineering Research Institute, Seismological Society of America, and California Governor’s Office of Emergency Services.

The Kircher team took new findings on earth movement from the USGS and the HAZUS technology developed by the National Institute of Building Sciences, and applied that science to the inventory of buildings by census tract across 19 counties in the Bay Area.

For information visit www.1906eqconf.org.

Topics California Catastrophe Natural Disasters Trends Earthquake