More earthquake faults discovered at the Salton Sea
- From: Charles <ckraft@xxxxxxxxxxxxxxxxx>
- Date: Mon, 27 Jul 2009 22:55:31 -0700
Sound waves bounced off the lake bed reveal the shifting blocks of
crust, leading to a new theory of how the ground is sinking and
stretching near the infamous San Andreas fault.
By Jia-Rui Chong
July 28, 2009
By bouncing sound waves off the floor of the Salton Sea, researchers
have discovered more than a dozen previously unknown earthquake
faults, leading to a new theory of how the ground is sinking and
stretching near the infamous San Andreas fault.
Danny Brothers, lead author of a study published Sunday, said the new
understanding of the area's seismic mechanics does not appear to
suggest that a massive quake on the San Andreas is more imminent than
previously believed. Earthquake scientists have been interested in the
region, about 140 miles east of Los Angeles, because the southernmost
end of the San Andreas disappears at the banks of the Salton Sea.
"By all reports, the San Andreas is considered overdue," Brothers, a
geophysics graduate student at UC San Diego, said Monday. "What this
does is gives us more information to assess it. Now we can start to
run some scenarios on how earthquakes beneath the Salton Sea might
affect the state of stress on the San Andreas and vice versa."
Scientists have not had very detailed maps of the crust under the
Salton Sea, in part because underwater conditions have made it
difficult to employ traditional techniques for studying faults. For
years, scientists inferred fault locations there by studying
earthquake data. The recordings led scientists to suggest that blocks
of crust were swiveling side to side, but generally moving
horizontally.
For the new study, published Sunday in the journal Nature Geoscience,
Brothers and colleagues crisscrossed the Salton Sea with a sonar-like
instrument. Measuring the reflections of sound waves gave the
researchers images of sediment layers down to about 200 feet below the
lake bed.
They discovered about 15 to 20 relatively short faults angled toward
the San Andreas.
Their data led them to propose that the crust in the area is being
pulled apart by the San Andreas and the nearby Imperial fault. When
the crust pulls apart, it subsides and dips into a basin, rather than
just shifts horizontally, Brothers said.
Craig Nicholson, a research geophysicist at UC Santa Barbara who was
not involved in the Nature paper, said the more detailed picture of
the lake bed raises new questions about the region's seismic
complexity.
"It's not clear what the connection is between the features they're
seeing and the faults at [greater] depth," where earthquakes are
thought to originate, Nicholson said. "Maybe the earthquakes are
reflecting a slightly older pattern, and the sediment cover is telling
us more about what's happened more recently."
jia-rui.chong@xxxxxxxxxxx
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