Unusual Seismic Signals in the Sevier Desert, Utah Possibly Related to the Black Rock Volcanic Field

On September 12, 2018 and April 14, 2019 shallow (<2.5 km from the surface, <1 km relative to sea level) earthquakes (M-w 4.0 and 4.1, respectively) struck a relatively aseismic area in south-central Utah, within the Black Rock Desert volcanic field. Seismic waveforms are dominated by long-period energy, no clear direct S-wave arrivals, and signal durations of similar to 100 s. Using co-seismic interferograms, we detect clear and distinguishable surface deformation confirming the shallowness of the two mainshocks, while full moment tensor solutions rule out an isotropic source, such as an explosion or collapse. For the April 2019 sequence, we build an earthquake catalog using a dense temporary geophone array. The enhanced earthquake catalog shows a rapidly decaying aftershock sequence, with 85% of aftershocks occurring during the first three hours. Combining these observations, we argue that these earthquake sequences are related to the Black Rock Desert volcanic field. Plain Language Summary On September 12, 2018 and April 14, 2019 shallow (<2.5 km from the surface, <1 km relative to sea level) earthquakes (M-w 4.0 and 4.1, respectively) struck southcentral Utah, within the Black Rock Desert volcanic field. Seismic signals from these earthquakes were unusual and uncharacteristic for tectonic earthquakes, and we rule out the possibility of a mine collapse or explosion. We confirm that the two earthquakes are shallow and find distinguishable surface deformation. For the April 2019 sequence, we used advanced techniques in order to detect more earthquakes, taking advantage of a dense temporary network located near the mainshock. The new earthquake catalog, that contains three times more earthquakes than originally cataloged, shows that the earthquake sequence lasted for a few hours. Based on these findings, we hypothesize that the shallow earthquakes are related to the Black Rock volcanic field.

Automated summary

The shallow earthquakes that struck the Black Rock Desert volcanic field in Utah in September 2018 and April 2019 were unique in their seismic signals, surface deformations, and aftershock sequences, ruling out an isotropic source. The enhanced earthquake catalog constructed using advanced techniques revealed a short-lived aftershock sequence, leading to the hypothesis that the shallow earthquakes are related to the volcanic field.