THE BUZZ: Aftershock

By on August 31, 2016

Saturday’s 4.8 quake is nothing to shrug off.

Former state geologist Wallace Ulrich says a 4.8 earthquake is a substantial event that warrants attention.

Former state geologist Wallace Ulrich says a 4.8 earthquake is a substantial event that warrants attention.

JACKSON HOLE, WY – Saturday afternoon’s earthquake felt in Jackson Hole was the weekend topic of conversation. The event itself was not unusual for this region. But the real-time monitoring stations delivering data to scientists, and the wildfire on social media including “Did You Feel It” reports and a video of rock slides in Granite Creek are the aftershocks of the modern day seismic event, never before possible since our planet began taking shape.

For the record, it was a 4.8-magnitude quake, though Dr. Bob Smith, a professor emeritus of geology and geophysics at the University of Utah, made readings of a 5.0M. The discrepancy is nothing to quibble over, Smith conceded. “I’ll take my readings over [USGS]. We have all the instruments up there,” he said.

The quake struck at 2:47 p.m. on Saturday, epicentered 5.2 miles ENE of Bondurant just off Forest Road 30043 in the heart of the Little Jennie Ranch. It is estimated to have occurred about 6.2 miles beneath the surface—exactly standard for tremblers in that region.

Former state geologist Wallace Ulrich said of the tremor, “A 4.8 is a substantial event in this region and should get our attention. And it did. It will be looked at.”

Here comes the science

We live in of one of the most complex and active geological regions in the world; within stone’s throw of the largest volcano on the planet, so big it needs the word “super” in front of it. Far beneath the comfort of our homes lie cracks, fissures and fault lines revealing millennia reverberations of an unsettled Earth. Evidence of seismic activity needn’t be gleaned solely from sensitive monitoring stations in place in Yellowstone, Jackson Lake Dam, and even Budge Butte. The naked eye can clearly see the chaos of the outré Gros Ventre Range, for example, where jagged peaks thrust skyward, topple on their sides and fold over each other. It’s freakish landscape.

“It’s one of the most wonderfully complex geological systems around. There are numerous fault structures in there,” Ulrich said. “The event recently was quite normal for that area and zone. The mountains are still building there. The Earth is constantly chugging around and sliding. It’s a very complicated region and that’s exciting as hell.”

Western Wyoming is crisscrossed with fault lines—Teton, Hoback, Star Valley, Greys River are just some of the subterranean fractures known to scientists. Move northeast from where Saturday’s quake struck into the Gros Ventre toward Crystal Creek and a map of the fault lines looks like a child’s doodling—frenetic scribbling so helter-skelter it’s a wonder the forest holds itself together for even an hour.

“That Crystal Creek area around Red Rock Ranch is a hinge of sorts. There is a lot of adjustment and stuff still going on. Some day we’ll find some student that wants to study this. There simply aren’t enough studies being done right now or money to do them with,” Ulrich said.

The region where Saturday’s quake hit is in part of a sinking basin called the Hoback Formation. It’s comprised partly of a tilted (40 degree eastward dip) ridge overridden by the Jackson-Prospect thrust sheet along the Prospect fault, and folded along the Little Granite-Monument Ridge anticline at the upper end of the Green River Basin. (More than you wanted to know?)

It’s eastern boundary is truncated by the Cache Creek trust fault while a smaller syncline of the Gros Ventre Range also bumps up against the region to the northeast. The whole mess took shape in the middle Paleocene to early Eocene ages and hasn’t stopped moving since.

“The [epicenter] is a sort of toe where a frontal push is activated with the overthrust. It’s a very active area that puts pressure on the larger mountain range to the north,” Ulrich said. “[The recent quake] might be a precursor or could provide energy up into the Teton Fault region enough to kick it over, or it could do the opposite and take away pressure. Looking at the tiny swarms before and after the event—it appears to be a very localized earthquake and taking care of itself.”

Shake it up

Tremors were felt as far away as Rock Springs and Evanston, according to the USGS website. Residents in Bondurant and Cora had predictably the more intense experiences to report.

Stacy Noland was on water when the earthquake hit. “I was kayaking at Leigh Lake when the water started to violently churn, but there was no wind. The last time I experienced such an event was when I was fishing on a lake in central Washington and a major earthquake hit Seattle,” he said.

Wilson resident Rose Porcello lives at the northern end of Fish Creek. She said the shaker reminded her of her days growing up in New York City. “At first it felt like a train, like a subway. Then I remembered I wasn’t in New York and the TV was shaking. I got up to hold it still. Some pictures fell off the wall,” she said.

At the top of the gondola at Couloir Restaurant, a rolling sensation was felt by several tourists for about 15 seconds.

Christi Biolchini Yannelli captured some amazing footage of several rockslides streaming down cliffs in the Granite Creek drainage where she was fishing.

Town public works director Larry Pardee noted that Budge slide moved a tenth of an inch as a result of the quake. That’s as much as the butte usually moves in a month.

Fracking to blame?

So did fracking, about 100 miles away in Jonah Field, cause the earthquake? That’s what many wanted to know in the hours following the event, particularly after Smith noted the quake took place “in an area of relatively low seismicity.” Natural gas and oil extraction activities have been linked with earthquake swarms in Oklahoma and Texas.

Ulrich responded with an emphatic “no.”

“I’ve studied the hell out of hydraulic fracturing for decades, for two governors. Comparing what is happening in Oklahoma to the Jonah Field is absurd,” Ulrich said.

Other scientists who have not worked for pro oil and gas governor Matt Mead agreed.

Dr. Ernie Majer, Ph.D. at the University of California-Berkeley, boasts an impressive resume during his distinguished career. When contacted about Jackson Hole’s shaker, Majer looked at the data and said he didn’t think the earthquake had anything to do with waste injection. But he noted it’s often difficult for many experts to be impartial.

“Sometimes scientists get caught between a rock and hard place. Oil companies remind colleges like University of Oklahoma, for example, that they are big donors. That’s why USGS has taken an independent stance,” Majer said.

Gail Atkinson, professor of earth sciences at Western University in London, Canada, said without even studying the region she can say fracking didn’t cause Saturday’s quake. “The location of your recent event, in an area that does not usually get events of this size, raises a question of whether the event might have been induced,” Atkinson said. “However, in this case it appears unlikely based on the believed depth of the event [10 to 14 kilometers], which is too deep for induced events—which are usually in the depth range from 2 to 6 kilometers.” PJH

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