Randy Mann: Northwest coast due for a major earthquake
Within the last week, there have been three major earthquakes, one in the San Francisco Bay Area, one off the South American coastline near Peru and another near Chile. In August, there have been five quakes measuring 6.0 or higher – the other two were in Wenping, China, and the Federated States of Micronesia.
The California quake was centered about 6 miles outside the city of Napa, which is east of San Francisco. It struck very early Sunday morning and had a magnitude of 6.0.
According to the U.S. Geological Survey, the first quarter of 2014 had more than double the rate of earthquakes higher than a 7.0 when compared with the average since 1979. A sampling since 1979 may not be large enough to make this type of comparison, but it does make many scientists wonder when the next big one will strike.
The largest earthquake in the U.S. – and second-largest worldwide – was a 9.2-magnintude temblor on March 28, 1964, at Prince William Sound in Alaska. Anchorage was completely devastated. Other notable major U.S. earthquakes include a 7.8-magnitude quake in San Francisco in 1906, a 6.9 at Loma Prieta in the Bay Area in 1989, a 6.7 in Northridge near Los Angeles in 1994, a 6.8 in Western Washington in 2001, and a 6.7 in Hawaii in 2006. More recently, a 7.9-magnitude temblor hit the Aleutian Islands on June 23.
The largest recorded earthquake was of 9.5 magnitude in Chile in 1960.
Earlier this summer, the U.S. Geological Survey updated its national seismic hazard map from 2008. The coastline from Northern California to British Columbia has been listed as a high-risk zone for a major earthquake. The shifting of the Earth’s crust leads to increasing stress. For the past 300 years, the Juan de Fuca plate off the Northwest coast has been colliding and diving under the huge North American plate. This area of stress along the Pacific coast is called the Cascadia subduction zone. In 1700, an estimated 9.0 mega-thrust earthquake hit the Northwest and created a giant tsunami that hit Japan.
It’s not a question of “if” the next major quake will hit the Northwest coast, but “when.” And when it does, it will likely cause catastrophic damage to the major Northwest cities. However, the Cascade Mountains would likely deflect the major earthquake waves to the north and south, so the effects of this future quake would probably not be quite as strong across the Inland Northwest.