There remains a lot of mystery behind central Idaho's 6.5-magnitude earthquake that rocked the state on March 31.
But with each aftershock, experts become closer to developing a full understanding of the earth-shaking event, according to Idaho State University geosciences professor Glenn Thackray.
“It’s a very complex geologic situation out there and there is a lot of information gathered on how much the ground moved up and down and things like that,” said Thackray, who added that there has been no “earth-shaking” discovery yet about the quake.
There have been 282 aftershocks greater than 2.0 magnitude stemming from the March 31 temblor. That initial 6.5-magnitude earthquake occurred below the headwaters of the Middle Fork of the Salmon River near Stanley and 44 miles west of Challis.
Thackray said the rate of aftershocks is slightly above average and they should stop within a few weeks without causing harm.
He said Boise State University installed seismographs to record data in the area of the earthquake a day after it occurred. That will allow seismologists to more precisely identify the location of the 6.5 magnitude earthquake and learn about the land movement caused by it.
“Everything we know about the fault is coming from the aftershock patterns and where the aftershocks are,” Thackray said. “They are forming kind of a very broad line which is probably showing where the fault is and we’re just waiting for more information to come in as the aftershocks continue. We learn a lot from the aftershocks.”
Thackray said it will take one to two months before there is a good understanding of what happened with the earthquake, which was the largest in Idaho since one near Borah Peak in 1983 that had a magnitude between 6.9 and 7.3.
There has been no evidence that any portion of the fault involved in the most recent earthquake is visible at the surface. That makes geologists’ jobs more challenging in understanding the fault, but it's possible that snow is covering an area where it reached the surface.
“The snow messes everything up,” Thackray said. “Once the snow melts, people will be able to get out there and inspect the ground and some of the satellite images will work better then.”
Thackray has familiarity with another central Idaho fault.
Ten years ago, he discovered the Sawtooth Mountains fault that goes from the foot of those mountains and under the town of Stanley. It causes a large earthquake about every 5,000 years, he said.
The fault was found using LIDAR, a tool to record elevation measurements from aircraft-mounted lasers at a rate of 25,000 pulses per second and can have a vertical precision of about 6 inches for a detailed topographic map.
While that fault did not cause the latest major earthquake, he was able to alert the town to be prepared for a major earthquake.
“I hope we convinced people that they need to be prepared for an earthquake,” Thackray said. “This wasn’t the earthquake, but there was an earthquake in that area. So hopefully we did some good.”
Thackray has been in the profession for 35 years but has not felt an earthquake since 2011 when he was in New Zealand. He was on the lawn at Idaho State University's campus during the latest major central Idaho earthquake.
But there have been notable earthquakes in the region that he has not felt.
Salt Lake City experienced a 5.7-magnitude earthquake in mid-March, the strongest on record in the city. Soda Springs had a 5.3 earthquake in 2017.
But Thackray still has the joy of learning about the aftermath of the latest quake and more about the Sawtooth fault. Plus he's pleased that other experts around the nation are taking interest in central Idaho too.
“That area has not been interesting to most geologists throughout the country for a long time. Now, everybody is interested in that area,” Thackray said. “The central Idaho earthquake hazards will be getting a lot of attention over the next few years and that’s good because there’s a lot that we don’t know.”