Earthquake strikes Utah amid COVID-19 pandemic

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By Tiegan Hobbs, Ph.D., Postdoctoral Seismic Risk Scientist, Temblor (@THobbsGeo)

As residents prepared for a pandemic, a magnitude-5.7 quake shook Salt Lake City, causing a chemical spill in the nearby mine and closing the airport.

Citation: Hobbs, Tiegan, 2020, Earthquake strikes Utah amid COVID-19 pandemic, Temblor, http://doi.org/10.32858/temblor.078

At 7:09 a.m. local time on March 18, 2020, the ground started shaking in Salt Lake City, Utah. The earthquake had a magnitude of 5.7, releasing 11 times less energy than the smaller of the two 2019 magnitude 6.4 and 7.1 Ridgecrest events in California. Despite being relatively small, the event closed down the Salt Lake City Airport and was felt as far away as Raleigh, N.C.! Within the first three hours, more than 30 aftershocks were recorded, leaving residents of this usually pleasant city feeling uneasy — particularly during the early stages of a viral pandemic.

This quake serves as a reminder that Mother Nature doesn’t take a break just because there’s a pandemic. Luckily, preparations made for COVID-19 also prepare people for dealing with an earthquake.

An aerial view of downtown Salt Lake City and the nearby snow-capped Wasatch Mountains. At the edge of the Wasatch Range lies the major and seismically active Wasatch Fault. Today’s earthquake occurred on an unmapped fault to the west. Image credit: Ron Reiring, CC BY 2.0.

Scientists expect earthquakes here

Firstly, some comfort: Earthquakes of this size are expected in the Salt Lake City area. Despite being inland, Utah is still in “earthquake country” due to its numerous faults. The University of Utah reports that there have been six earthquakes with magnitude 3.0 or larger since 1962. That year, a magnitude-5.2 earthquake struck less than 3 miles (5 kilometers) from today’s epicenter.

Overall, the maximum probable earthquake shaking you can expect in your lifetime in Salt Lake City is a level 5 on the Modified Mercalli Intensity (MMI) scale. The March 18th earthquake, however, had a maximum shaking of level 8. The reason this is so much higher is that global models of maximum shaking don’t include the effect of basins. In this region, the Salt Lake Valley Basin is 1000-2000 feet deep (Radkins et al., 1989), which contributes to a stronger shaking here than in the nearby mountains. This has been observed for Seattle (Pratt et al., 2003), Mexico City (Asimaki et al., 2019), and other cities built atop deep basins.

Temblor map showing the location of the March 18 mainshock and its aftershocks in the first few hours. The earthquakes are on unmapped faults to the west of the West Valley Fault Zone and the Wasatch Fault. Although the quake registered a maximum shaking of MMI 8 (VIII), the PUSH model predicts a maximum probable lifetime shaking of only MMI 5 (V) here. Image credit: Temblor.

Earthquake preparedness in the time of COVID-19

Salt Lake Mayor Erin Mendenhall was quick to make a public statement regarding the earthquake and the ongoing novel coronavirus pandemic. She reminded residents that in “some really strange ways,” being prepared for a pandemic means they were already prepared for an earthquake: shelter in place, with pantries stocked with a couple of weeks’ worth of nonperishable foods and well-supplied first aid kits.

Additionally, being at home tends to reduce injuries and fatalities in earthquakes, caused by damaged large industrial, commercial or government buildings made from unreinforced masonry or concrete.

That this earthquake occurred during an evolving viral outbreak response, however, draws attention to the difficulty of responding to multiple disasters simultaneously. No casualties are expected from Utah, but an estimated 2.6 million people were exposed to shaking in this earthquake. With a healthcare system that is already stressed by the ongoing COVID-19 pandemic, it’s easy to imagine the devastating impact of a larger earthquake in Utah or any other populated place.

Double disasters have happened before too. During the 1991 eruption of Mt. Pinatubo in the Philippines, Typhoon Yunya passed over the region, unleashing strong winds and rain on the volcano and the nearby capital city: Luzon. In this case, much like today’s earthquake in pandemic-ready Utah, the second hazard actually lessened the negative impacts of the first. The Guardian reported that some of the particles that were spewed from the second-largest volcanic eruption of the century would have damaged the ozone far more seriously had the typhoon not shifted the plume.

Although most combinations of disasters are worse than the sum of their parts, the good news is that preparing for a joint occurrence of hazards is done the same way as preparing for a single hazard: keep your emergency kit well-stocked and have a communication plan with your loved ones. And as with any unfolding disaster, listen only to official news sources like local, state and federal emergency management operations to help limit the spread of misinformation. This was essential in Utah, for example, as rumors swirled nearly instantly after the earthquake about imminent large aftershocks.

Concerned about earthquakes? Check your risk at Temblor.

Earthquake causes spill at the nearby copper mine

As reported by Mary Richards from KSLM Local News, the earthquake caused a hazardous material spill at the nearby Kennecott Copper Mining facility. The fire from this hazardous spill produced a large vertical plume of smoke. At this time, it is unknown if there was any other damage to the mining facilities or the nearby tailings ponds, which have previously been identified as potentially seismically susceptible. The Utah National Guard was deployed to help manage the situation, although all mine staff and personnel have been reported safe.

Earthquake near, but not on, the major Wasatch Fault

The majority of earthquakes in the Salt Lake City area tend to locate along the north-south-aligned Wasatch Fault Zone. This fault is “the longest continuous, active [extensional] fault (343 km) in the United States,” and tends to rupture in a major earthquake every 395 years (Machette et al., 1991). It defines the eastern edge of the Basin and Range Province, where extension across the western states pulls the crust apart into a series of valleys called “grabens”.

Further reading: Learn more about the Basin and Range Province here.

However, today’s earthquake appears to have ruptured on an unmapped fault to the west. Though near the West Valley Fault System, which is thought to be dynamically linked to the Wasatch Fault (DuRoss & Hyland, 2015), the March 18, 2020 earthquake occurred on a northeast-southwest trending extensional (normal) fault farther to the west. Aftershocks appear to locate along an east-west trending lineation, which may be related to the stress field imposed on the region by the nearby Great Salt Lake.

Further Reading: Check out this map from the Utah Geological Survey showing historical seismicity in the state.

Works Cited

Asimaki, D., Villa, J. M., Ayoubi, P., Franke, K., & Hutchinson, T. (2019, March). Mexico City Basin Effects: Past, Present, and Future. In Eighth International Conference on Case Histories in Geotechnical Engineering.

DuRoss, C. B., & Hylland, M. D. (2015). Synchronous ruptures along a major graben‐forming fault system: Wasatch and West valley fault zones, Utah. Bulletin of the Seismological Society of America, 105(1), 14-37.

Machette, M. N., Personius, S. F., Nelson, A. R., Schwartz, D. P., & Lund, W. R. (1991). The Wasatch fault zone, Utah—Segmentation and history of Holocene earthquakes. Journal of Structural Geology, 13(2), 137-149.

Pratt, T. L., Brocher, T. M., Weaver, C. S., Creager, K. C., Snelson, C. M., Crosson, R. S., … & Tréhu, A. M. (2003). Amplification of seismic waves by the Seattle basin, Washington State. Bulletin of the Seismological Society of America, 93(2), 533-545.

Radkins, H., Murphy, M., & Schuster, G. T. (1989). Subsurface map and seismic risk analysis of the Salt Lake Valley. Utah Geological and Mineral Survey.

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