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PHOTO CREDITS: PORTLAND MONTHLY
According to LiveScience.com, A fault near Portland, Oregon is at risk to cause an earthquake of up to a magnitude of 7.4, which it did as recently as a thousand years ago. This event would create very strong shaking, damage property, and potentially threaten lives.
New research into the Gales Creek fault, which is located 22 miles west of Portland, reveals that earthquakes have occurred on this fault three times over the past nine thousand years. Fortunately, this fault rarely produces major quakes, researchers reported on October twentieth in the Bulletin of the Seismological Society of America. They reoccur every four thousand years or so, and there is no evidence that the fault is currently at high risk for rupture.
The new findings suggest the need to study other nearby faults for signs of recent earthquakes. “Many faults in the region are of interest based on their proximity to population centers,” said Allison Horst, a paleoseismologist at the Washington State Department of Resources.
To trace the history of the Gales Creek fault, Horst and her team set up five-foot deep trenches using shovels and a backhoe. Inside the trenches were layers of sediment that had been deposited over thousands of years, including dark, charcoal-rich soil left by past floods. Broken parts of these layers show evidence of past earthquakes. Since the charcoal is organic material the researchers could use radiocarbon dating, which uses the decay rate of radioactive isotopes of carbon to determine the age of the soil.
The geologic history showed three earthquakes large enough to disrupt the Earths’ surface. The oldest dates back to 8,800 years, the next 4,200 years ago, and the most recently at 1,000 years ago. This averaged out to a significant earthquake around every 4,000 years for this fault in particular.
The next step, Horst said in a statement, is to study other faults in the region for signs of ancient earthquakes. Learning when other faults cracked could unveil a connection between faults, which would further clarify the earthquake hazards around Portland.
ARTICLE: JOSEPH MODICA
SCIENCE/HEALTH EDITOR: KYLE SMITH