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SACRAMENTO -- While
agreeing that a period of relative quiet
on the San Andreas Fault may be nearing
an end, acting California State
Geologist Michael Reichle emphasized
Thursday that a widely publicized report
by a University of Oregon geologist is
not a prediction of a cataclysmic
earthquake in the immediate future.
“It’s fair to say
that every day we’re one day closer to
the so-called Big One,” said Reichle,
who heads the California Geological
Survey for the state’s Department of
Conservation. “But people shouldn’t jump
to the conclusion that this report means
the Big One is imminent. It is simply
another reminder that we need to be
prepared for the inevitability of major
earthquakes in California.”
Added Department of
Conservation Director Darryl Young:
“It’s not the end of the world, but it
should be the beginning of your
preparation.”
University of Oregon
geologist Ray Weldon presented a paper
about his research at the annual meeting
of the Seismological Society of America
on Wednesday. Dr. Weldon’s trenching
work on the San Andreas Fault at
Wrightwood, 60 miles northeast of
downtown Los Angeles, indicated that,
since 3000 B.C., historically long
periods of relatively little seismic
activity on that section of the fault
have been followed by clusters of large
earthquakes.
The last major
rupture of the southern San Andreas
Fault occurred on January 9, 1857. The
Fort Tejon earthquake may have been the
most powerful in California history,
with an estimated magnitude of 7.9.
While the quake left a 220-mile surface
scar, it killed only two people because
of its remote epicenter and the
relatively small population in the area
at the time. A temblor of that size in
the modern-day Los Angeles area could
kill hundreds and do billions of dollars
in property damage.
The southernmost
section of the San Andreas Fault in the
Coachella Valley has not had an
earthquake in approximately 300 years.
“Scientists have long
considered this section of the fault to
be ripe for an earthquake,” Reichle
noted. “What’s new in Dr. Weldon’s
report is the indication of a pattern:
quiet periods, clusters of earthquakes,
quiet periods, clusters. We know that on
the scale of years earthquakes can
cluster. Between 1812 and 1906, there
were five earthquakes magnitude 7 or
greater in California, two of them along
the San Andreas fault near Los Angeles.
Since the San Francisco earthquake, 98
years ago Sunday, the San Andreas has
been fairly quiet.
“Dr. Weldon may be
right that we are nearing the verge of a
switch, but the timing of that switch is
highly uncertain. It could be 30 years
or more. We don't yet completely
understand the dynamics of the earth's
crust.”
In 2001, California
Geological Survey seismologist Tousson
Toppozada presented a paper to the
Seismological Society of America stating
that historical data indicated a pattern
that could mean increased seismic
activity in the Bay Area within 20 years
of the 1989 Loma Prieta earthquake.
In addition to
studying and mapping earthquakes,
landslides and mineral resources, the
Department of Conservation administers
programs to safeguard agricultural and
open-space land; regulates oil, gas and
geothermal wells in the state; promotes
beverage container recycling; and
ensures reclamation of land used for
mining.
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