World news – Unusual earthquakes mark the volcanoes in central Utah


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March 2, 2021

by Paul Gabrielsen, University of Utah

If you drive south on Interstate 15 through central Utah and look west anywhere near Fillmore, you will see smooth hills and fields of black rock. The area is aptly called the Black Rock Desert. It might not look like much, but you will see some of Utah’s volcanoes.

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Two earthquake sequences in September 2018 and April 2019 drew the scientists’ attention to the Black Rock Desert. The sequences, which included the mainquakes and their aftershocks, were very different from the Magna earthquake that hit the Wasatch Front in 2020 and other Utah earthquakes. The Black Rock sequences were captured by the Utah Regional Seismic Network and a nearby temporary seismic device monitoring a geothermal well. Earthquakes in the Black Rock Desert are rare, and seismic records from these earthquakes provide a glimpse into the Black Rock Desert’s volcanic system, which while showing no signs of an eruption, is still active. A study of the earthquake sequences is published in Geophysical Research Letters.

« The results showed us that we should pay more attention to the Black Rock area, » says Maria Mesimeri, a postdoctoral fellow at the University of Utah Seismograph Stations. « We need to improve seismic and volcanic monitoring in this area so that we are aware of small changes that may occur. »

The earthquake sequences with major shocks of magnitude 4.0 and 4.1, respectively, were taken from both the Utah Regional Seismic Network as well as a dense temporary network of seismometers deployed as part of Utah FORGE, an experimental geothermal project funded by the U.S. Department of Energy and operated by the University of Utah, about 30 km south of the Black Rock Desert in near Milford, Utah. The temporary network enabled researchers to see more aftershocks than usual. For example, in the April 2019 sequence, the regional network detected 19 earthquakes. However, the dense temporary network discovered another 35 quakes. Each additional aftershock provided a bit more information for seismologists studying the sequence.

The Black Rock sequences showed some interesting features that set them apart from the 2020 Magna sequence and other Utah earthquake sequences. While the initial Magnaquake occurred at a depth of about six miles below the surface, a typical depth for Utah earthquakes, the Black Rockquakes were much shallower – about 1.5 miles below the surface.

« Because These earthquakes were so shallow, « says Mesimeri, » we were able to measure the surface deformation [due to the quakes] using satellites, which is very unusual for such small earthquakes. « 

Mesimeri and her colleagues also found that the quakes generated much lower frequency seismic energy than is usually the case with Utah quakes. And one of the main types of seismic waves, shear waves or S waves, was not recognized in the Black Rock sequences.

All of these signs suggest that the Black Rock sequences have a very different origin than the Magna- Sequence generated by the movement of the Wasatch bug. The Black Rock quakes, on the other hand, could have been caused by continued activity in the Black Rock volcanic field.

What are volcanoes doing in central Utah? The Wasatch Mountains (and Wasatch Fault) form the eastern edge of a region called the Basin and Range that extends west to the Sierra Nevada. The province is stretched apart by plate tectonics, and this stretching thins the crust, allowing more heat to rise from the Earth’s interior. In the Black Rock region, this heat led to the eruption of basaltic lava up to about 9,000 to 12,000 years ago.

« Our results suggest that the system is still active and that the earthquakes are likely the result of movement related to liquids in the general area were, « says Mesimeri, referring to potentially magma or heated water. « The earthquakes could be the result of the rock compressing the fluid, or the result of deformation from fluid movement that strained the surface defects. »

Activity in a volcanic field does not mean an eruption, and Mesimeri says there is no evidence to support it that an eruption in the Black Rock Desert is imminent. But, she says, it’s an area that geoscientists might want to watch a little more closely.

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Related title :
Unusual earthquakes highlight volcanoes in central Utah


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