June 2016 – CALIFORNIA – Analysis
of GPS data has revealed new areas of motion around the San Andreas
Fault System. Using data collected by the EarthScope Plate Boundary
Observatory’s GPS array, researchers identified 125-mile-wide “lobes” of
uplift and subsidence. Over the last several years, the lobes, which
straddle the fault line, have hosted a few millimeters of annual
movement.
Computer models simulating the San
Andreas Fault System have predicted such crustal movement, but the areas
of motion hadn’t been physically identified until now. Researchers used
advanced statistical modeling to identify the movement among the
inevitable statistical noise that comes with monitoring minute movements
in the Earth’s crust.
“While the San Andreas GPS data has
been publicly available for more than a decade, the vertical component
of the measurements had largely been ignored in tectonic investigations
because of difficulties in interpreting the noisy data,’” lead author
Samuel Howell, a researcher at the University of Hawaii at Manoa,
explained in a news release. “Using this technique, we were able to
break down the noisy signals to isolate a simple vertical motion pattern
that curiously straddled the San Andreas Fault.”
The validity of the vertical patterns
was confirmed by the fact that similar motions were predicted by an
earthquake model designed by researchers at the University of Hawaii’s
School of Ocean and Earth Science and Technology. “We were surprised and
thrilled when this statistical method produced a coherent velocity
field similar to the one predicted by our physical earthquake cycle
models,” said researcher Bridget Smith-Konter. “The powerful combination
of a priori model predictions and a unique analysis of vertical GPS
data led us to confirm that the buildup of century-long earthquake cycle
forces within the crust are a dominant source of the observed vertical
motion signal.” Researchers say their new findings — published in the
journal Nature Geosciences — could help scientists use smaller lobes of vertical motion to predict more significant ruptures. –UPI
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