A quake registering 5.8 woke up Fairfield residents around 12:30 a.m. last Thursday morning. The quake and a series of aftershocks originated south of Lincoln, Montana.
Here in Fairfield, I was in a deep sleep when I felt my bed shaking and a loud, repeating “bang.” The house was moving in rhythm to the banging sound.
At first, I thought a car had run off the road and hit my home, but the repeated movement, as if in a series of waves, pointed toward something other than a wayward driver. It couldn’t have been much of a threat, Ol’ Thump, curled up at the foot of the bed, didn’t budge.
Out of bed, I grabbed a flashlight and was headed out the front door to inspect the house for damage when, about 3 or 4 minutes after the first series of shakes, a second round hit.
It had been many years since I had been in a quake that felt so strong. Growing up near the famous New Madrid fault, quakes were a common occurrence. And when the New Madrid was quiet, we could always depend on the nearby Milan Army Ammunition Depot to shake things up when they exploded faulty ordnance in long pits.
Once I was certain it was a quake, I logged into the U.S. Geological Survey website to see if they were reporting the quake. It took about ten minutes for the quakes to show up on the USGS site.
By then, the quake was a major topic on Facebook. People in Fort Shaw, Great Falls and Helena were online, describing their experience.
Once the quake was reported on the USGS earthquake map, it was clear that the shaking was coming from the same area, south of Lincoln, where we reported a series of small quakes last year. In those earlier quakes, the magnitude was much lower.
Ronda Eustance Lopez of Fort Shaw said that she and her husband “heard a rumble and then the house started shaking… the bed was moving enough for our dog to come shooting out from under the bed, she was pretty freaked out.” Ronda said that they laid down and felt the second tremor and then the third one, about twenty minutes after the main quake.
An email to fellow newsies Roger and Erin Dey at the Blackfoot Valley Dispatch was quickly answered, confirming they were OK and that there were scattered reports around Lincoln of minor damage.
Bill Hansen, a geologist based Great Falls also described it as a “low rumble for about a minute that vibrated the house, similar to what we feel when a large truck rumbles down the road in front of our house.”
Doug Abelin, who lives near Lake Helena, told the Sun Times over the weekend that he was working in a bakery in Bozeman when the 1959 Hebgen Lake quake struck in southwestern, Montana, resulting in over 28 fatalities. “This was second only to that, excluding 1000 pound bombs in Vietnam.” Abelin added that last week’s quake was a “good jolt” and when his home shook for nearly 30 seconds made the quake “impressive.”
Nine hours after the first quake, a series of 16 were recorded, with the smallest having a magnitude of 3.1. The first quake was 13.6 kilometers deep; the second was 4.9 km underground. The shallowest was 6.6 km deep.
By Thursday afternoon, almost 15,000 people had reported to the USGS that they had felt the quakes. Twenty-five Fairfield residents reported that they felt the tremors, 48 in Choteau, five in Augusta and Fort Shaw. About 30 people in the Lincoln area told the USGS they felt it. Reports of the quake came from as far away as southern Alberta and British Columbia to the north; Idaho and NW Wyoming to the south.
About an hour after the quake, I took a ride into town to see if there were any broken windows along Fairfield’s Central Avenue. It was about as quiet as could be expected in Fairfield at 1:30 a.m. on a Thursday.
Geologist Bill Hansen said that in his opinion the quakes were occurring along the Lewis & Clark “line.” Plotted on the USGS site, the quake and aftershocks showed both a general north-south and east-west alignment. Hansen said the quakes were most likely the result of some slippage in an “ancient, deep zone of weakness, like the New Madrid.”
Included in a paper written by James W. Sears in 2009, a map is included that shows the Lewis & Clark Line, stretching from Idaho, near the Washington border, running southwest, terminating southwest of the Little Belt Mountains. Sears is Professor of Geosciences at the University of Montana.
By this past weekend, many more aftershocks were showing up on the USGS website near Lincoln, but they were of a low magnitude.