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SACRAMENTO -- Most
people know all about the largest
earthquake in California’s recorded
history: San Francisco destroyed by the
“Big One” and ensuing fire, 3,000 dead,
half a billion in damage in 1906 dollars
… right?
Perhaps. Some
scientists would argue that the “Biggest
One” occurred about 50 years earlier,
but because it didn’t have nearly the
human impact as the San Francisco quake,
it has been largely forgotten.
The 150th anniversary
of the Great 1857 Fort Tejon earthquake
is January 9. Estimated to have been a
magnitude 7.9 on the San Andreas Fault,
the temblor caused damage from Monterey
to San Bernardino County. It was felt as
far north as Marysville, as far south as
San Diego and as far east as Las Vegas.
But because it was centered in a
sparsely populated area – the entire
population of California was only about
350,000 at the time -- it only directly
caused one death; a woman in Gorman was
killed when an adobe house collapsed.
Not only is the
earthquake often overlooked, but it’s
probably misnamed. The epicenter, most
scientists agree, was somewhere near the
isolated southeast Monterey County
community of Parkfield, not at Fort
Tejon, which is on “the Grapevine” in
Kern County. It is known as the Fort
Tejon quake because that was the largest
settlement impacted by the shaking. Two
buildings were declared unsafe at the
fort, which is about 4½ miles from the
fault, and three others were damaged
extensively.
“Although there were
some rudimentary seismic instruments at
a few institutions in Europe, there was
no accepted universal scale by which to
measure how large either the Fort Tejon
or 1906 San Francisco earthquakes were,
so there’s no definitive answer to the
question of which was larger,” said
State Geologist Dr. John Parrish, head
of the California Geological Survey (CGS).
“While size does
matter in an earthquake, location is
equally important. A magnitude 6
earthquake directly under a city is a
lot more significant than a magnitude 7
-- which releases 32 times as much
energy -- in the middle of the sparsely
populated desert. We know that the Fort
Tejon earthquake was very large because
it left a trace at the surface 225 miles
long and caused the surface of the earth
to
shift along the fault
about 30 feet. But because it didn’t
impact a major population center, it
isn’t nearly as well remembered as the
1906 earthquake.”
However, Parrish
noted, the anniversary should serve as a
reminder to California residents to be
ready for large, damaging earthquakes
and other natural disasters. The basics
of how to be prepared and what to do if
an earthquake occurs can be found on the
California Department of Conservation
Web site
here.
“History tells us
that at some point in the coming decades
there likely will be very large
earthquakes along the San Andreas
Fault,” Parrish said, adding that the
recurrence rate for a Fort Tejon-like
earthquake is about 200 years. “We can’t
predict earthquakes and we can’t stop
them; we can only prepare to survive
them. Communities and cultures that
recognize the geologic hazards that
surround them and learn to prepare
survive natural disasters. For an
example of those who don’t, visit
Pompeii.”
The shaking caused by
the Fort Tejon quake reportedly lasted
for more than a minute and perhaps as
long as two minutes. It temporarily
changed the direction of the Kern
River’s flow, stranded fish far from the
banks of the now-vanished Tulare Lake,
and sloshed water out of the Mokelumne
and Los Angeles rivers. It caused some
artesian wells in the Santa Clara Valley
to go dry and formed new springs near
Santa Barbara and San Fernando. The
ground shaking partially collapsed the
church tower at the old Spanish mission
in Ventura. There was a report of trees
sinking into the ground – possibly due
to liquefaction – between Stockton and
Sacramento.
A repeat of the Great
1857 Fort Tejon Earthquake today would
cause significant loss of life, and
damage in the billions of dollars.
Wrightwood, Palmdale, Frazier Park,
Taft, and other communities that didn’t
exist or had tiny populations in 1857
are on or near the trace of the rupture
of the Fort Tejon quake. The U. S.
Interstate 5 highway -- the main land
route between Northern and Southern
California -- runs right by the fort,
now a state historic park. While
Interstate 5 crosses the San Andreas
Fault only once, branches of the
California Aqueduct System carrying
water from Northern to Southern
California cross it at several
junctures.
“When people think of
the `Big One’ in Southern California,
this is the earthquake they’re talking
about,” said Dr. Michael Reichle, Chief
Seismologist for CGS. “The San Andreas
Fault trends to the east and north of
Los Angeles. While it’s unclear how the
shaking would impact the very tall
buildings in L.A., the real damage in a
repeat of the Fort Tejon earthquake most
likely would occur in the Inland Empire.
The fault runs right through Palmdale
and near San Bernardino, for example.
“In Los Angeles, I’d
be more concerned about a significant
earthquake on the Newport-Inglewood or
Puente Hills faults than on the San
Andreas, although a big quake on the San
Andreas near the Salton Sea area could
channel quite a bit of energy into the
L.A. Basin.”
Since the 1933 Long
Beach earthquake, the State of
California has developed codes and
regulations to build safer structures.
CGS, part of the California Department
of Conservation, is involved in a
variety of earthquake safety-related
projects. These involve research,
mapping and monitoring.
CGS
employs geologists, seismologists and
other Earth scientists, and is one of
the oldest geological surveys in the
United States.
In addition to
mapping and studying earthquakes and
other geologic phenomena, the Department
of Conservation classifies areas
containing mineral deposits; ensures
reclamation of land used for mining;
regulates oil, gas and geothermal wells;
promotes beverage container recycling;
and administers agricultural and
open-space land conservation programs.
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