Earthquakes in the Northwest are more frequent

A rare 5.8 earthquake struck Montana around 12:30 a.m. MDT early Thursday morning. I chatted with many people and the sound sleepers didn’t feel anything. But, many felt the quake as far west as Spokane. My bed shook quite a bit during this event. It’s almost hard to believe, but I lived in California for over 30 years and the largest earthquakes I felt were here in Coeur d’Alene and in northern Vermont back in 2002.

The epicenter of the one last week was about 6 miles southeast of Lincoln. Following the 5.8 magnitude event, there were 10 aftershocks, according to the U.S. Geological Survey, including a 4.9 magnitude five minutes later. Yes, I felt that one too. The other quakes ranged from 3.5 to 4.4 over the following 2 1/2 hours.

Fortunately, Thursday’s earthquake had no reports of injuries or major damage. It was the strongest to hit western Montana since a 5.6 magnitude hit a nearby area in July of 2005. There was also a concern that this event was related to Yellowstone’s supervolcano. Scientists say that the earthquake was the result of the movement of the well-known Lewis and Clark Fault. Therefore, experts say a large eruption at Yellowstone is still “very unlikely” in the near future.

Many people still talk about the four earthquakes that hit Bonner County near Sandpoint on April 23 and 24 that measured near 4.0. According to earthquaketrack.com, there have been over 40 earthquakes across our region over the past year. Most, however, are so small that no one feels them, usually measuring less than a 2.0 in magnitude. Prior to Thursday’s shaker in western Montana, Wallace measured a 3.2 magnitude earthquake on Nov. 10, 2016. On June 21, there was a small 2.5 magnitude event in Grangeville.

Although, major earthquakes in the Pacific Northwest are not very common, scientists are concerned about a potential large event along the West Coast of Washington. Based on historical evidence, there was a huge megathrust earthquake on Jan. 26, 1700, that was known as the Cascadia earthquake. It happened across a 620-mile area along the Cascadia subduction zone from the middle of Vancouver Island in British Columbia, southward along the Pacific Northwest coast down into northern California. The magnitude was estimated between 8.7 and 9.2. The devastating Alaskan earthquake in 1964, the second largest recorded in history, was a 9.2.

The big quake in 1700 was believed to have generated a large tsunami that hit the coast of Japan. It may also have been linked to the Bonneville Slide. This was a major landslide that dammed the Columbia River near Cascade Locks in Oregon. The Native Americans referred to this as the “Bridge of the Gods.” However, other investigations state that the landslide occurred around 1450 based on radiocarbon dating and dendrochronology (tree rings).

Geologic evidence shows that a major earthquake that would likely cause heavy damage to Seattle, Portland, Vancouver and other big cities along the Pacific Northwest coast, occurs approximately every 400 to 500 years. So, the chances of a major event within the next 30 years are relatively small.

A recent geophysical survey confirms the presence of earthquake faults (cracks in the earth) beneath the Spokane area. It extends from the airport toward Hillyard and ends near the North-South freeway project. Since this fault is not very long, it’s not likely that Spokane would be hit by a major earthquake.

In 2001, the Latah Creek Fault was believed to be responsible for a swarm of 105 small earthquakes in the Spokane area. Most were less than a 4.0 magnitude, but there is the potential for small tremors in this area.

In terms of our local weather, the early portion of this month has been hot. Temperatures late last week were close to the 100-degree mark. The last time it was 100 degrees was on Aug. 13, 2015. The summer of 2015 was a scorcher across our region. There were an additional three afternoons In July of 2015 with highs at or above the 100-degree mark. The hottest day ever recorded in Coeur d’Alene happened on Aug. 5, 1967 when a high of 108 degrees.

Cliff and I see more hot and dry weather across the Inland Northwest into the middle of the month. Then, we could see a few scattered afternoon and evening thunderstorms move up from the south before more hot and dry weather returns toward the end of the month.

By the way, last week I wrote a feature on the upcoming eclipse and mentioned a story about a condemned astronomer. Several readers told me about a movie that has this plot called, “A Connecticut Yankee in King Arthur’s Court” made in 1949. It was a musical comedy and starred Bing Crosby. Thanks Scott and Howard!

Contact Randy Mann at randy@longrangeweather.com