Popular songwriter Carole King, known for “You’ve Got a Friend” and “I Feel the Earth Move”, Idaho shortly before 6 p.m. Tuesday. All of a sudden, the earth moved under his feet.
It was an earthquake. And not a small one – a magnitude of 6.5. It was centered under the Sawtooth Mountains about 80 miles northeast of Boise, but it rocked the state capital for a fraction of a minute. It was even felt in northern Utah, which was shaken up by a 5.7-magnitude quake near Salt Lake City less than two weeks ago. Earthquakes are unrelated.
It is the most powerful earthquake to hit the Gem State since a magnitude 6.9 earthquake in 1983, in which two Challis children were killed by falling debris. No incident or serious damage was reported following the earthquake on Tuesday, which was centered in a sparsely populated area.
And while thousands were caught off guard, baffled by the unexpected earthquake, some scientists – such as Glenn Thackray, a geoscientist at Idaho State University – had already encouraged people near the epicenter of preparing for an earthquake a decade ago.
“We quickly learned that this area was likely to suffer from earthquakes,” said Thackray, who discovered the sawtooth fault in 2010. This fault did not cause the earthquake on Tuesday, which occurred rather produced on a border cutting this fault. Anyway, a decade ago, Thackray set out to educate residents of the city of Stanley about the potential for a major earthquake.
“I was able to tell people up there [about] common sense things to do, “he said. “When it comes to houses and the like, telling people to use common sense in an earthquake-hit country, like putting shelves on the wall … removing heavy objects from the high shelves, especially near their beds.” “
Tuesday’s earthquake was center just outside Stanley.
Stanley Mayor Steve Botti told the Idaho statesman that the tremors were so intense that he could not go down the stairs. “Stuff was flying everywhere,” he said.
Discover a fault
Finding an unknown failure is not an easy task. Faults are elements of the earth’s crust that sometimes extend tens of kilometers underground. Defects do not only occur at the interface of two tectonic plates; instead, a defect occurs whenever the bending, twisting, stretching or compression of a plate results in finer limits which press against each other.
But in the late 2000s, Thackray used lidar, or light sensing and telemetry, which uses laser lights, to map the surface of the Earth. His team was able to “remove” the trees digitally, leaving behind a three-dimensional model of the surface at a resolution of two or three feet. It was then that he noticed something quite unusual.
“We found a surface feature called the fault escarpment,” said Thackray. “This … step in the landscape was a flaw. As soon as we saw this, we knew that the fault was active and we suddenly have confirmation. “
How big is this fault?
“If we were walking towards the mountain front and arriving at this escarpment, we would have to climb 20 to 25 feet [at a 45 degree slope], ” he said.
Earthquakes are rare, but they are significant
Thackray estimates a 25-foot gap “represents three earthquakes in [the past] 15,000 years, “with a slip of about eight feet over each.
“It doesn’t go very often,” he said.
This is a theme of the Idaho earthquakes, according to Thackray. There are fewer daily rumbles that are ubiquitous in places like California or Oklahoma, and rather higher periodic earthquakes.
“There are a lot of active faults that break very rarely,” said Thackray. “Many of them … seem to be pretty locked up. Nothing to suggest that the block slides at all; this is very quiet. “
But suddenly there is an earthquake.
By studying the sediment layers in the region, Thackray finally concluded that the fault generates large earthquakes every 4000 years or so.
“These faults don’t break so often,” said Thackray. “But the simple calculation sometimes is that it will break again. There is no reason to believe that these defects disappear. “
Where was Tuesday’s earthquake?
Tuesday’s earthquake was not exactly the fault itself.
“It looks like it was a fault that crosses the end of the sawtooth fault,” he said. “The fault we looked at is a bit like an inclined sheet of plywood that extends underground … this one is at an angle to the [Sawtooth Fault].
” [The earthquake] had a different type of movement, and it looks [was] very close or faulty. There were two earthquakes in 1944 and 1945, and it seems that it may have been the fault that caused these earthquakes. “
Thackray said the region remains somewhat seismically misunderstood, but said he was optimistic that Tuesday’s earthquake would shed light on the complex processes at work below the surface.
The point to remember, however, he says, is that Idaho is not immune to high-level earthquakes. And while the aftershocks from Tuesday’s earthquake will die out in the days and weeks to come, he warns residents that the sawtooth fault is active. But when will the next big one hit? This is the always important question.
“I would tell people in this region that in an hour between 1,000 and 1,000 years,” he said jokingly.
Tuesday’s events, however, offer advice to Idahoans far and wide: always be prepared.