The first studies on Idaho’s magnitude-6.5 earthquake are out. Here’s what they tell us.
Nicole Blanchard, Idaho Statesman
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BOISE (Idaho Statesman) — Nearly nine months after the second-largest recorded earthquake in Idaho’s history, researchers with Boise State University published the first analyses of the temblor, shedding more light on an incident that has captured scientists’ attention as smaller quakes continue.
In late November, a team of BSU geosciences experts published a report on the low-frequency sounds emitted by the March 31 earthquake. In December, some of the same researchers published a piece in GeoScienceWorld’s Seismological Research Letters detailing the “tectonic framework, seismicity and aftershock monitoring efforts” of the earthquake.
The magnitude-6.5 earthquake occurred along the Sawtooth fault near Stanley, and since March thousands of smaller earthquakes have occurred in the same area — including nearly 100 in the last two weeks.
“Prior to March, I certainly was aware that the Sawtooth fault was seismically active, but I never explored the details of that fault system beyond some background,” said Boise State seismologist Lee Liberty, who co-authored both papers, in a phone interview.
“The problem is there really is no or was no expert on the Sawtooth fault in terms of its earthquake history,” Liberty added. “The last time we’d seen earthquakes on that fault was back in the 1960s.”
Liberty and his research partners found that the Sawtooth fault extends farther than previously thought, as does the nearby Lost River fault where Idaho’s largest recorded earthquake, the 1983 Borah Peak quake, originated. Liberty said continued seismic activity is drawing attention — and with it, more research and understanding — to the Sawtooth fault.
BOISE STATE RESEARCHERS PREDICT MORE SHAKING
Though researchers rushed to set up earthquake detection equipment in the Stanley area following the March 31 earthquake (amid heavy snow and COVID-19 concerns), real-time data from the equipment was not available due to poor cell service. Liberty said they’ve since been able to go back over that historic data and locate the quakes’ epicenters with more precision.
“There were some surprises in the sense that some of the earthquakes are migrating farther to the south,” Liberty said.
In the weeks since the team’s research was published, Liberty said, the earthquakes are moving even farther south along the fault.
“Almost all of (the earthquakes) during 2020 were north of Redfish Lake,” he said. “Now we’re seeing earthquakes occurring farther south along the fault. The concern that would raise for me is … we know based on the work of (Idaho State University seismologist) Glenn Thackray that the area around Redfish Lake and farther south has moved with surface rupturing-type events in the past.”
The researchers noted in their December paper that the Sawtooth has a history of seismic events that rupture the earth’s surface dating back thousands of years. The recent string of quakes is somewhat unusual in that it hasn’t appeared to break through the earth.
That ties into another conclusion of the recently published research — that the shaking isn’t done in Idaho. Liberty said there’s “a potential for another large earthquake to come” in the area, potentially rupturing the earth’s surface, though he said he’s not able to offer a probability of such an event.
“What I tell people is that I’m not going to predict another large earthquake, but it would be consistent with historic events,” Liberty said. “Maybe a magnitude-6, maybe a little larger. We just don’t know. We’re not really out of the woods just yet.”
Historically, larger quakes have occurred in the area within a year of one another. But Liberty’s research asserts that shaking, particularly of smaller quakes, will likely continue for years.
Liberty said following the initial magnitude-6.5 earthquake and its stronger aftershocks, Stanley Mayor Steve Botti asked him when the shaking would stop.
“My assessment is that it’s not going to stop any time soon,” Liberty said.
IDAHO EARTHQUAKE PROMPTED SURGE OF NEW RESEARCH EFFORTS
The ongoing quakes have made the Sawtooth fault a hot topic in the geoscience community.
“There’s been tremendous interest,” Liberty said. “(Our research) is one of the most-read stories in the earthquake community.”
The Sawtooth fault was discovered in 2010 by Idaho State’s Thackray, but information on the fault has been sparse as Thackray planned further research. Shortly after the March 31 earthquake, Thackray told the Statesman he thought the Sawtooth fault may have been involved but early evidence wasn’t conclusive.
“Where this magnitude-6.5 earthquake initiated, there was no mapped fault,” Liberty said in January. “When we look at aftershock patterns … there are aftershocks in faults that have not been identified. Efforts (in seismology) have not been on mapping Central Idaho.”
“The Stanley earthquake illustrates that potentially damaging earthquakes can occur away from mapped active faults, and, as with this earthquake, can leave little or no evidence in the geologic record,” the Boise State researchers’ paper concludes. “From this earthquake, we anticipate a renewed interest in the seismotectonics of Central Idaho, and we anticipate advancing our understanding of this earthquake sequence through continued aftershock monitoring and analysis.”
Liberty said Thackray has plans to map the area’s faults more extensively this summer, while Liberty and his fellow researchers at Boise State will continue to examine numerous aspects of the area.
“Now it looks like a fuzzy blob of earthquakes, but we’re going to be able to focus that,” he said. “We’re going to have a much better handle on the faulting characteristics (of the area).”
Liberty said all the attention means researchers are looking at all different aspects of the earthquakes and, as a result, will have a much better understanding of Central Idaho’s various faults.
The last year’s seismic events have also raised awareness of just how seismically active Idaho is (it’s one of the most active areas in the country), as well as its relative lack of earthquake readiness compared to places like California or Japan.
“In my mind, this was the perfect earthquake in that it was large enough to garner the attention of the citizens of Idaho but remote enough to not really cause significant damage,” Liberty said. “The possibility of earthquakes next to population centers (in Idaho) is very real, so that’s what we need to raise awareness to.”