You probably felt the M 5.7 earthquake in SLC at 7:09 AM MDT on March 18, 2020, with an epicenter 6 km (3.7 mi) north-northeast of Magna, Utah. It was Utah’s most powerful quake since 1992, when a magnitude 5.9 hit the St. George area.
- Source KDVR
While centered in a more remote area, reducing the impact, there was plenty of damage, including the Salt Lake Temple, where the statue of Angel Moroni lost its trumpet, and power was lost to some 50,000 homes, although restored to all but 2,600 by the evening.
At least six aftershocks had been recorded within 20 minutes of the main quake, and as of March 26, a total of 591 aftershocks were been observed and located by the University of Utah seismic network, including two M 4.6 events that occurred at 08:02 and 13:12 MDT on March 18.
According to instrumentation records dating back to 1962, and historical records dating back to the1850s, the USGS says Utah can expect earthquakes greater than magnitude 5 to happen once every 10 years, and quakes greater than magnitude 6 happen once every 50 years.
Most of those will occur along the Wasatch Fault, a serious fault line running 220 miles from central Utah, north along the Wasatch Front through Salt Lake City into Idaho, and which is still being uncovered, and raises some concerns given the 180,000-plus homes along its path.
But, did you know ….Kamas valley has it’s own fault-line, the East Kamas Fault (No.2391), which runs down the valley from the Mahogany Hills, NE of Oakley, to the stop-light in Francis.
In fact Kamas has a Seismic monitoring station as part of the University of Utah earthquake research system, on top of Hoyt Peak.
Nowhere near as dangerous as the Wasatch Fault, the E Kamas fault is still active and has seen several M 1.0-2.8 magnitude quakes in the past 50yrs.
- Source Utah Geological Survey
We’ve highlighted the E Kamas fault line in the yellow box, while the rest of the map shows the area from the Salt Lake to Roosevelt in the east.
The small dark dots are low magnitude quakes (<2.9) that we’ve experienced since 1962 when more thorough records began. The biggest quakes since 1850 (>5.0) are listed in the left bottom corner and numbered 1-18. For example, number 8 in the right lower corner was a 5.3 NE of Hanna, in 1950.
You can see the E Kamas fault has seen some low-level activity since 1962, with small dots running along the fault, but nothing too “earth shattering”.
In fact some of those quakes may have been caused by seismic activity in the Park City and Heber/Midway areas, which are much more prone to large movement.
While this data only goes to 1983, you can see that the three largest quakes (No’s 1,2 & 5) in the table occurred in the Heber area.
While this fault is “poorly understood”, its dormancy is likely due to the period it was formed (around 130,000 yrs ago) and the sort of soil deposits left as the earth settled.
It’s called a Quaternary Fault since it’s thought to have developed in the Quaternary period of the Earth’s history, which ranges from today to 2.6million years ago. The endpoint has changed several times in the past few decades, but importantly, it measures the time that humans have been on the Earth, and during which the tectonic plates of the continents have been most stable.
The late Quaternary refers informally to the past 0.5-1.0 million years. Faults that have slipped during this time are sometimes considered active. Our fault most likely formed within the past 100-200,000 yrs and should be much less active as a result.
In more complicated geological terms, to quote the USGS,
“Geomorphic expression – Range-front escarpment. Alluvial deposits that are estimated to be 130-140 ka (Sullivan and others, 1988 #4508) cross the inferred trace of the fault and appear to be unfaulted. Degraded scarps on old alluvial-fan remnants could be the result of faulting, but the presence of a parallel scarp (terrace riser) cut by the Weber River suggests an erosional origin is more likely.”
Oh, in case you’re wondering, it moves about 0.2mm yer year, so Kamas residents won’t have to change their address to Park City for a few more thousand years.
For those interested in the geology of the Valley, take a look at this website which shows the different types of rock and soil that make up the Kamas valley.
And for those interested in the history of Utah’s geography and geology try these two official websites.