Scientists are eagerly awaiting the return of a “slow earthquake” that could give them clues to when and where the next major quake will strike the Pacific Coast of North America.
The recently discovered phenomenon is believed to occur about every 14 months, which would put the next event anytime now, but people are unlikely to feel anything because it will occur 12 to 25 miles (20 to 40 kilometers) below the earth’s surface.
“We’re all rushing in every morning and every night looking at the records to see if it has started,” Garry Rogers, a seismologist with the Pacific Geoscience Center in Sidney, British Columbia, said Friday.
The coastal region of northwest Washington state and southeast British Columbia is prone to earthquakes, and scientists warn that the area gets hit with a devastating shake of magnitude 9 about every 500 years.
Shift in thinking
Scientists discovered the phenomenon several years ago when they realized that a tectonic plate, which is normally pushed northeasterly by another plate in the area, would abruptly change its direction for several weeks.
“Instead of this slip happening over a few seconds it happens over a few weeks, so it is, in some sense, like a slow earthquake,” Rogers said.
The discovery made scientists rethink theories about how the pressure caused by the colliding plates is built up to the point that it results in a large earthquake.
“It’s not a straight line at 45 degrees, it’s like a staircase. ... We have no idea where we are on the staircase, but eventually we get to the top and have a big earthquake,” Rogers said.
The Big One of 1700
The region’s last magnitude-9 earthquake was in January 1700, destroying coastal Indian villages on Vancouver Island and creating tidal waves that reached Japan. The region now includes cities such as Seattle and Vancouver.
The Geological Survey of Canada and the University of Washington have set up special monitoring equipment, and scientist hope this year’s data will give them a more accurate map of where a major quake would strike.
Researchers thought they had spotted the start of the phenomenon in late April near Centralia, Wash., south of Seattle, but the activity quieted down before it reached north to Vancouver Island.
“Right now, we’re just waiting,” Rogers said.
