Newfound Cracks in Northwest Shake Up Quake Outlook

Seismologists have identified two previously unknown and potentially active faults near the capital of Washington state.

The newfound cracks in the Earth's rocky plates near Olympia, Wash., create a more complex picture of the earthquake risks in the Pacific Northwest.

More work is required before scientists can say whether these two faults are active, but if they are, then "presumably it would redistribute the hazard" of a quake in the region, said U.S. Geological Survey geophysicist Thomas Pratt, a member of the study team.

Some areas of the Pacific Northwest would be more at risk of a quake than previously thought, and the risk in other areas would drop.

"If they turn out to be active, it would increase the hazard in Olympia, but you can only have a certain number of earthquakes in an area, so the risk would decrease somewhere else," Pratt told OurAmazingPlanet.

Researchers from the University of Washington and the USGS collected what's known as marine seismic reflection data, which uses sound waves to look into the Earth in the same way that sonograms do in medical imaging. This technology allows them to examine faults beneath the surface in the Tacoma and Olympia areas of Washington, by the southern Puget Sound.

Beneath Puget Sound, layers of glacial deposits left in the past 16,000 years provide a record of recent faulting. Here, researchers found two faults in young deposits near Olympia. Because the faults cut through strata that may have been deposited during or after the glacial retreat, the faults appear to have had recent activity and therefore could pose an earthquake hazard to the population of the southern Puget Sound region.

Other researchers are investigating the faults, using instruments that can probe even deeper beneath the surface, to determine if the faults are active.

The study is detailed in the August edition of the journal Bulletin of the Seismological Society of America.

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This article was provided by OurAmazingPlanet, a sister site to LiveScience.