March 24, 2011 in Washington Voices

Mann: Clues about earthquakes don’t eliminate guesswork

RandyMann
 

I’ve received numerous emails about a recent report that another major earthquake potentially striking the Seattle area in the near future.

Seattle lies within the volatile “Ring of Fire.” This region has been formed as the result of huge continental plates moving and sliding into one another. Many are familiar with the North American plate and the Pacific plate sliding past one another, creating the notorious San Andreas Fault.

But a smaller plate, called the Juan de Fuca, is located off the British Columbia, Washington, Oregon and extreme Northern California coastline. New evidence suggests that it is currently pressing against the North American Plate causing uplift and stress. Eventually, it’s expected that the ground will break, perhaps causing another mega-thrust earthquake that could rival the recent Japanese disaster.

But, no one knows when that may happen or how strong the quake might be. According to a recent National Geographic documentary, there have been 19 major earthquakes in the northwestern U.S. over the last 10,000 years. The last one, based on carbon dating and Japanese writings, occurred around 1700. That major quake also triggered a tsunami that practically wiped out the Japanese coastlines. Based on this average, a major earthquake near Seattle may not occur for hundreds of years.

On average, since 1900, there is one quake with a magnitude of 8.0 or higher each year worldwide – in 2007 there were four. There are about 17 quakes between a 7.0 and a 7.9 per year. According to the U.S. Geological Survey, “Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant.”

There has also been a large increase in the number of earthquakes that we locate each year because of more seismograph stations in the world and improved global communications. There are about 8,000 seismograph stations now compared to 350 in 1931.

In terms of our weather, La Nina continues to hold on to life. Our overall pattern still points to cooler and wetter weather into next month. However, there will be days of sunshine and pleasant temperatures. It looks like we’ll get a break from the cool and showery conditions next week before more valley rains and mountain snows arrive again in early April.

I wouldn’t take off those snow tires yet. It’s still possible that we could see a storm or two drop some measurable snow in the lower elevations in April. But, once we get into May, we should see some better weather with only occasional rain showers and thunderstorms.

Contact meteorologist Randy Mann at randy@ longrangeweather.com.


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