Earthquakes in the Midwest with threats in the Northwest

Residents in the Midwest have been concerned about the recent increase in earthquake activity in southern Illinois. Since the middle of November 2023, there have been three earthquakes measuring from a 2.5 magnitude in early March of this year, to 3.6 magnitude last November.

Scientists say that these types of events, especially within months of one another, are not completely unusual. The region of this activity is north of the infamous New Madrid Seismic Zone, which extends from extreme southern Illinois down into Missouri, Arkansas and western Tennessee. This large fault produced four major earthquakes in 1811-12, ranging from 7.0 to 7.5 magnitude. Since that date, there have been thousands of smaller ones in that part of the country.

Earthquake experts believe the recent increase in earthquakes in southern Illinois is not connected to the New Madrid region, but many are uncertain as to why there has been an increase in activity in this part of the country. However, the region of the three recent earthquakes is approximately 100 miles north of the northern edge of the New Madrid Seismic Zone.

Here in the Pacific Northwest, major earthquakes are not very common, but scientists are concerned about a potential large event along the northwestern coastline known as the Cascadia subduction zone. Based on historical evidence, there was a huge megathrust earthquake Jan. 26, 1700, that happened across a 620-mile area along the region from the middle of Vancouver Island in British Columbia, Canada, 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 magnitude. The largest earthquake ever recorded happened in Chile in 1960 with a magnitude of 9.5.

Prior to the event in 1700, based on estimated geologic evidence, there may have been seven major earthquakes in the last 3,500 years. According to the National Oceanic and Atmospheric Administration, research from cores obtained from the seafloor indicates that there have been more than 40 major earthquakes in the region over the past 10,000 years. Some experts say that the Pacific Northwest is “overdue” for a major earthquake and there is a 37% chance that the region could experience one of at least a 7.1 magnitude within the next 50 years.

In March 2020, there was a magnitude 6.5 earthquake that hit Boise and other parts of southern Idaho. Scientists believed that this was the result of the 40-mile-long Sawtooth Fault that runs near Stanley, Idaho, and Redfish Lake. However, a recent study published in the Seismic Record indicates that the 2020 earthquake may be linked to an undiscovered fault. Most of the earthquakes in Idaho are typically associated with the Yellowstone Hot Spot, also known as a supervolcano.

Strong earthquakes are not common in North Idaho, but April 23, 2015, a series of small earthquakes shook the Sandpoint area that were also felt in Coeur d’Alene and other areas. The following morning, April 24, a 6.1 quake was reported off the coast of British Columbia. A rare 5.8 earthquake struck Montana in July of 2017. I remember chatting with many people and the sound sleepers didn’t feel anything, but many felt the quake as far west as Spokane.

Earthquakes in our region may be a little more common than we think. There was a 2.1 magnitude tremor near Mullan on Feb. 18 and one measuring 2.7 near Fairchild Air Force Base on Sept. 12, 2023. According to the USGS, Coeur d’Alene has a moderate risk for earthquake activity with about an 11-12% chance of one measuring at least a 5.0 in the next 50 years. According to VolcanoDiscovery.com, over the last three years, there have been 102 earthquakes of at least a 1.5 magnitude within 62 miles of Coeur d’Alene. Since 1900, Kootenai County has reported 51 earthquakes with magnitudes above 3.0 and up to 4.2.

In terms of our local weather, since the snowfall returned Feb. 26, 14.5 inches have been reported in Coeur d’Alene as of late Saturday, taking the seasonal total to 47.7 inches. The normal for an entire season is 69.8 inches.

The early portion of the week will feature more rain and snow in the lower elevations. Then, conditions are expected to turn drier and warmer late this week and into the middle of next week. High temperatures are expected to climb into the 50s, and perhaps around the 60-degree mark, in Coeur d’Alene and surrounding areas, which will start to feel like spring. But don’t be fooled, toward the end of next week, another round of moisture is likely to move across the region. In fact, there’s the chance of more measurable snowfall in the lower elevations, especially as we get toward the end of the month.

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Contact Randy Mann at randy@longrangeweather.com.