Major Northwest quake may be a ways off yet

Last week I wrote about major earthquakes, including the possibility of one along the Pacific Northwest coast. Many of the big shakers are felt in Alaska and California.

My wife, Sally, and I lived in California for over 30 years, but the biggest earthquake we felt was when we lived in Vermont. That 5.2 event in April of 2002 was quite a surprise, but it goes to show that earthquakes can strike in any location. Prior to that event, I had produced a local story about the possibility of an earthquake in the Northeast. Some people snickered at me for that story, but they weren’t laughing when the ground shook.

Over the last year or so, it was reported in numerous articles that the northwestern portion of the U.S. may be hit by a massive earthquake in the near future. Cities and towns from British Columbia in Canada would feel the effects from the earthquake, including Seattle, Portland and Vancouver, B.C.

So how do scientists know that a major earthquake will strike the northwestern coastline? Because it’s happened before. Geologic and other evidence suggests that an estimated 8.7 to 9.2 earthquake hit that area on Jan. 26, 1700. The event was so large that it likely generated a giant tsunami that struck Japan. Japanese records do confirm the event in January of 1700. Along the Washington coast, many trees were drowned as evidenced from tree ring data; entire forests were lowered along the coastline.

Some scientists speculate that this event will be so strong that it will destroy thousands of homes and other buildings and devastate the region’s power grids. They also say that a mega-tsunami would be generated within 15 minutes of the earthquake, which would “create a 700-mile-long liquid wall” along the northwestern coastlines. Death tolls would be in the thousands or even the tens of thousands. This report has led to a lot of concern for people living and around the region.

I have seen a number of articles and features that mention this type of event could happen soon. However, based on historical evidence, others say the chances of this occurring within the next 25 to 30 years are relatively small. Another major earthquake is “inevitable” for the Pacific Northwest coastal regions, but the big question is “when”?

Prior to the event in 1700, based on estimated geologic evidence, there may have been seven major earthquakes in the last 3,500 years, perhaps about 500 years apart. Research from cores obtained from the seafloor indicate that there have been 41 major earthquakes in the past 10,000 years. Other research points out that big northwestern earthquakes may have occurred around 1310 A.D., 810 A.D., 400 A.D., 170 B.C. and 600 B.C. Back in 2010, scientists predicted a risk of 37 percent that the region could see a magnitude 8 or higher earthquake within the next 50 years.

The Earth’s land is constantly moving as we live on tectonic plates. In the Northwest, the Juan De Fuca plate off the Northwest Coast is literally diving under the huge North American plate to the east, which is called subduction. This region extends over 600 miles from northern Vancouver Island to Cape Mendocino in northern California. This process has formed the Cascade Range and volcanoes in the northwestern U.S., including Mt. Rainier and Mount St. Helens. The subduction is also creating stress in the rocks and over time, the rocks snap and can lead to what is called a mega-thrust earthquake with a magnitude of 8 or higher.

Many have also asked how our region would be impacted by such a massive earthquake. Well, thanks to the Cascade Mountains, the bigger or more devastating waves generated from the earthquake would likely travel more in a north to south direction. However, we would feel the shaking that would probably lead to some damage and perhaps widespread power outages. I wouldn’t lose any sleep over this, but it’s not a bad idea to have some kind of preparation.

Now, about our weather.

We’ve received more than double the normal amount of precipitation for March as El Nino seems to be weakening. I still see a normal to slightly drier than normal weather pattern in April to around the middle of May. There will, however, be occasional showers and thunderstorms, but Cliff and I don’t see an endless series of storms moving through the region during that time.

Scattered showers and thunderstorms are also expected for this summer of 2016. In other words, it shouldn’t be quite as dry or as hot as it was in 2015.

Contact Randy Mann at randy@longrangeweather.com