If the Bay Area were
rocked by a huge tremor today as powerful as the 1906 San Francisco
earthquake, the human toll could be worse than it was 100 years ago,
with as many as 3,400 killed, a quarter-million families homeless and
up to 140,000 buildings wrecked, according to a study released today.
The most immediate explanation is that more than 10 times as many
people live or work in reach of the San Andreas fault, which is capable
of tearing the Earth at thousands of miles an hour as it did at dawn
April 18, 1906. But the lethality and destruction also reflects the Bay
Area’s embrace of older but seismically unsafe buildings that, often as
not, house the elderly and poor — the most ill-fated of the next big
quake.
"As a result, those buildings sit in their original
conditions, even deteriorating, waiting for the next earthquake," said
Jack Moehle, director of the Pacific Earthquake Engineering Research
Center at the University of California, Berkeley.
Earthquake experts ran computer simulations of a similar,
magnitude 7.9 earthquake hitting the region today and calculated that
the shaking — and unleashing of hundreds of fires — would cause $150
billion in damages. It would rival the double punch of hurricanes
Katrina and Rita as the worst natural disaster in U.S. history but
arrive without days of warning.
BART’s Transbay Tube would flood or float free of its
underwater ballast and, with the westernmost lines, be out of
commission for two years. Some of the Bay Bridge would collapse.
Remarkable seismic engineering would save the main San
Francisco International Airport terminal, but its runways would buckle
and be unusable.
Odds are good that multiple Delta levees would fail, causing
an inundation of saltwater that would cut off fresh water for 23
million Southern Californians and 7 million acres of farmland.
The economy of the region wouldcome to a standstill and take months, possibly years, to recover.
But what structural engineers and scientists commissioned by
the 100th Anniversary Earthquake Conference discovered is that the Bay
Area is vastly more resilient to earthquakes now than in 1906. Damages
would be 10 times greater if San Francisco and its neighboring cities
were still made of turn-of-the-century buildings.
Such a massive quake is not seen as imminent. The seismic
clock of the San Andreas, as much as scientists understand its cycles
of stress and rupture, is halfway to rebuilding the strain for a 1906
repeat and ticking. But for all faults in the Bay Area, there remains a
62 percent chance of deadly, if smaller, quakes by 2032.
But danger remains in the region’s small stock of mostly
older commercial and residential buildings of three types —
unreinforced brick, inflexible and unreinforced concrete frame
structures, and mostly wooden "soft-story" structures with weakly
braced garages or shops on the first floor — mostly built before the
advent of modern seismic codes in the mid-1970s. Earthquake engineers
call them "bad buildings" or "killers."
"Those buildings kill over half the people even though they
represent less than 5 percent of the buildings" in the region, said
Charles Kircher, a structural engineer who led experts in assessing the
potential damage across 19 counties.
Their report, "When the
Big
One Hits Again," concludes that the largest damages — about $34 billion
— will again be in San Francisco County, followed closely by Santa
Clara ($28 billion) and San Mateo counties ($26 billion). Alameda
County alone, primarily Oakland, could sustain $15 billion in damages,
comparable to all of the damage in Southern California from the 1994
Northridge earthquake. Another $15 billion in damages would be
scattered among the region’s 15 other counties.
Most of the collapses and deaths would come in older buildings,
in older neighborhoods. San Francisco brings the largest concentration
of both into the closest proximity to the fault. The city also has
tight clusters of wood-frame houses and apartments, favoring the spread
of fires.
The study projects 500 to 700 fires in the Bay Area, with 100
in San Francisco alone, raising the possibility for a repeat of the
three-day conflagration that in the 1906 quake destroyed 500 blocks of
the city and accounted for 80 percent to 90 percent of the damage.
"The fires will start, and if it’s a hot, windy day, I’m not
sure we’re going to put that fire out," Kircher said, recalling that
firefighters were on top of the smoldering grass that blew up into the
East Bay hills fire. "They were standing there, and they couldn’t stop
it. Thousands of homes later, they finally got it out."
For shaking and collapse, the deadliest buildings are large,
pre-1970s concrete-frame structures lacking steel reinforcement and
containing a lot of people.
