A Southern
California earthquake forecast based on computer models has successfully
pinpointed the location of nearly every major temblor to hit the region over the
last four years.
Using historical seismic records as
a base, the Rundle-Tiampo earthquake forecast has accurately predicted locations
for 15 of the last 16 temblors with magnitudes greater than 5.0 on the Richter
scale, all of which have occurred since January 2000. The forecast is currently
about halfway through its 10-year timespan.
"I have to say that it's gratifying,
though I'm not surprised," said Kristy Tiampo, an assistant professor with the
University of Western Ontario in Canada, during a telephone interview. "The
Southern California and Northern California seismic networks have quite good
databases, the best freely available data around."
Tiampo worked with colleague John
Rundle, director of Computational Science and Engineering initiative for the
University of California, Davis to develop the quake forecast model. The
forecast is one part of NASA's QuakeSim project aimed at developing new methods
and tools for accurate earthquake predictions.
"What we're going for with
[Rundle's] data is to make earthquake forecasting like doing weather maps," said
Andrea Donnellan, QuakeSim principal investigator at NASA's Jet Propulsion
Laboratory (JPL) in Pasadena, California. "So that every year or month, you can
update the map."
In addition to the Rundle-Tiampo
forecast, the QuakeSim project relies on archived seismic data, extremely
accurate global positioning measurements taken by space-bound satellites, as
well as detailed interferometric
synthetic aperture radar (InSAR) measurements to track surface
changes.
"It's mostly a mystery," Donnellan
told SPACE.com of the Earth's seismic
activity. "One of the things we're learning is that you can't study one
fault...each earthquake at one fault affects others."
Building a temblor
forecast
With funding from NASA and the
U.S. Department of Energy, Rundle and Tiampo pored through Southern
California seismic records from 1932 onward, inserting the data into a computer model
designed to seek out tremor hotspots within the state.
"The computer model simulates the Southern
California [seismic] network," Tiampo said, adding that in addition to using
earthquake data, the forecast also incorporated modeling techniques typically used for
neural net and turbulence simulations.
The Rundle-Tiampo forecast split the
southern half of California - from San Francisco down to the Mexican border -
into about 4,000 individual boxes and calculated the seismic potential for a
strong earthquake in each space between 2000 and 2009. Released in 2002, the
forecast has apparently pinned the location of 11 earthquakes, while four others
occurred within the two previous years.
The outstanding earthquake, a
5.2magnitude temblor that shook a region covered by the Pacific Ocean near San
Clemente Island, occurred on June 15, 2004. Rundle has said the forecast may
have missed the shaker because it was centered on a region near the edge of the
state's seismic network. That may have added an increased uncertainty to its
location, he added.
"What I think
these hotspots should really be used for is education...to make sure that gas
lines are up to code in these regions and acquire the resources to prepare
buildings for quakes," Tiampo said, adding that there are still just over five
years left to measure the forecast's effectiveness. "And I would also like to
see the model revised in upcoming years."
Estimating the magnitudes - in
addition to the location - of potential tremors and narrowing the
forecast timeline are prime targets for improvements, researchers
said.
"You would want to be able to give
a probability, such as between the next six months and two years, for a
possible earthquake," Tiampo added. "And then keep a running forecast going as the
system changes."
Spotting Earth strain from the
orbit
Both Tiampo and Donnellan agree that
while the Rundle-Tiampo forecast appears to be on the right track, it is
restricted solely to seismometer records. The model does not include data on the
slow deformation to the Earth's surface that can occur without registering on
the Richter scale.
"Seismometers only measure the
shaking action," Donnellan said, adding that earthquake researchers have
observed high strain within the hotspots targeted by the Rundle-Tiampo forecast.
That strain can slowly shift the
Earth's crust. For example, after the 1994 Northridge earthquake, which
registered 6.7 in magnitude, the surrounding mountains continued to move,
growing a full 12 inches (30 centimeters) taller, Donnellan said.
Donnellan said QuakeSim researchers
have demonstrated that InSAR measurements could detect high strain events from
space, but only by borrowing time with spacecraft that were not designed
specifically for the task.
A dedicated space instrument would
not only add to the baseline of earthquake data, but also reach temblor prone
regions like Turkey where large-scale seismic measurements are unavailable, or
Japan, where seismic network changes has made consistent long-term measurements
difficult to obtain, she added.
During an October 2004 workshop in
Oxnard, California, researchers gathered together to determine the requirements
necessary for a dedicated InSAR space mission.
"With a five-year mission, you could
pretty much map the surface strain on the entire globe," Donnellan said, adding
that such an instrument could also serve as a worldwide earthquake watchdog.
"Anything above a 5.0 you should be able to detect, which could be about 200
earthquakes a year."
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