Past offers lessons on future Big One
When the great Ft. Tejon earthquake ripped the San Andreas fault 150 years ago this week, the shaking was so powerful it shook the Kern River from its banks and for a moment made it run upstream, according to accounts from the day.
If such a quake occurred today -- and scientists say we are overdue for one in Southern California -- it would cause $150 billion or more in damage, disrupt water and power supplies for Los Angeles and pancake buildings from San Bernardino to the L.A. Basin.
But despite years of preparedness measures and improved building codes, scientists and safety experts say Southern Californians need only look to New Orleans and that city’s struggle to survive after Hurricane Katrina to understand the potential for great disruption if a major temblor strikes.
Though many newer buildings would survive, numerous high- and mid-rise structures built between 1933 and 1970 could collapse or suffer severe damage, they said. Water supplies and exit routes could easily be cut off.
Scientists hope to use the anniversary of the Jan. 9, 1857, quake in a yearlong series of preparedness campaigns aimed at shoring up residences and infrastructure.
Experts also will spend the year developing detailed scenarios about what would really happen if a magnitude 7.9 temblor -- the size of the Ft. Tejon quake -- were to occur along a length of the San Andreas in Southern California that scientists believe is overdue for a major quake: from the Salton Sea to Lake Hughes.
To kick off that effort, seismologists, engineers and emergency preparedness experts participated in a two-day scientific meeting Monday and Tuesday at USC, which houses the Southern California Earthquake Center.
One point officials made was that the Tejon quake was truly a massive temblor, the true “Big One” that people worry about.
Many mistakenly think that surviving a quake simply means cleaning up afterward and repairing damaged buildings, they said.
But the most devastating temblor that Southern Californians remember -- the 6.7 magnitude Northridge earthquake of 1994 -- is considered moderate by scientific standards.
A 7.9 magnitude quake on the San Andreas would do far more damage.
“We need to shift our thinking about earthquakes,” Ellis Stanley, general manager for the city of Los Angeles Emergency Preparedness Department, said at a news conference Tuesday. “The notion that all we can do is pick up the pieces afterward must be replaced with a new culture of readiness, where we act now to reduce our losses in the next big earthquake.”
Lisa Grant, an associate professor of social ecology at UC Irvine, said her research shows that past quakes on the southern San Andreas occurred more often than previously believed, at an average of once every 150 years or less.
That means the region of particular concern to scientists -- from the Salton Sea to Lake Hughes -- may be even more overdue for a powerful temblor than scientists thought, said USC earth scientist Thomas Jordan, who directs the Southern California Earthquake Center.
“That section of the San Andreas fault hasn’t ruptured since 1680,” Jordan said. “It’s at least 10 months pregnant.”
According to a report released by the group Tuesday, economic damage from a 7.9 quake on the southern San Andreas would total $150 billion. The vast majority of the economic damage would be in Los Angeles County, followed by San Bernardino and Orange counties.
The study did not look at the number of deaths and injuries that would be caused.
Scientists say they hope to ferret out such important details and gain a better understanding of the geological impact of a large quake on the southern San Andreas as they move forward with their work through this anniversary year.
Seismologist Lucy Jones of the U.S. Geological Survey said Tuesday that despite the potentially deadly impact of such a quake on the region, scientists have few details about how a major rupture on the southern San Andreas would occur and what the effects would be.
That is partly because for years, the scientific community mistakenly thought that Los Angeles, because of its distance from the fault, would be relatively immune to such a quake, Jones said.
Part of the renewed concern is based on the work of Swaminathan Krishnan, an assistant professor of civil engineering at Caltech in Pasadena. Krishnan has developed a model that uses new data on the way seismic waves move through the Earth to test models of real buildings to see how they would hold up during a big quake.
Studying the Tejon temblor itself rather than the southern San Andreas model that scientists also are analyzing, Krishnan found that even though the rupture was far away -- tearing along the San Andreas for about 185 miles from Parkfield to near Wrightwood, Los Angeles would be severely affected if it occurred again. The San Fernando Valley, he said, would be hit particularly hard.
The next step, Krishnan said, would be to input information on buildings in Southern California and develop computer models to show how they would fare.
Scientists also will spend the year studying the likelihood of a big break on the San Andreas, comparing the historical record of major ruptures on the fault to try to estimate when the next one will occur.
*
