More than 2,500 earthquakes occurred in and around Wyoming over the last year, but most of them went unnoticed by Wyomingites, according to a report on geological hazards released Thursday by the Wyoming State Geological Survey.
Earthquakes occur when built-up pressure becomes too great for the rock to bear. The rock fractures, largely along faults, or weak areas in the rock. The rupture then reverberates out, sometimes across long distances.
“An earthquake is basically rock breaking in the earth,” said Seth Wittke, manager of the geological hazards division of the WSGS. “It’s just crustal dynamics, where you have strain and stress and all kinds of different forces … Once enough stress builds up in the rock, then it breaks.”
Though 2,500 earthquakes may sound extreme, it is not atypical for Wyoming, which experiences less seismic activities than some states to the west, Wittke said.
Of the 2,558 earthquakes that occurred between November 2017 and October 2018, many were not strong enough to be felt by people on the surface, according to the report.
“A rule of thumb that I go by is if it’s under 2.5, it’s not typically felt by people,” Wittke said.
Nine earthquakes last year were measured at a magnitude of five or greater and dozens exceeded 2.5, including a 4.4 magnitude earthquake in Soda Springs, Idaho, in January. The aftershocks were felt across Star Valley, according to the WSGS report. People also reported feeling the effects of an earthquake north of Wheatland and in both Washakie and Hot Springs counties in the Big Horn Basin.
The source of some of these earthquakes may be in faults that are considered “modern” by geologists’ standards, according to the report. Those are ruptures that have occurred within the last 1.6 million years. There are more than 30 modern faults in the state. Most of these are on the western edge of Wyoming
Wyoming’s Yellowstone National Park in the northwest, populated by grizzlies, park employees and tourists, is the epicenter of much of Wyoming’s earthquake activity. It’s also the area where nearby residents were most likely to feel the effects of energy convulsing the ground over the last year. This is in part due to the Yellowstone Caldera and the movement of fluids both underground and on the surface.
The Wyoming Geological Survey has partnered with the U.S. Geological Survey, the Bureau of Reclamation and academia to study the modern faults in Jackson Hole and the Washakie Mountains, according to the report.
There were three notable landslides in Wyoming between November 2017 and October of 2018, noted in the report. The Porcupine Creek landside destroyed part of the Greys River Road in Lincoln County in April, affecting tourism in Alpine, followed by a smaller landslide that stranded campers in the area. In June, a slide destroyed two properties in Park County, near Crandall, according to the report.
The geological hazards data is available in a GIS map on the WSGS website. The WSGS also released summary reports on the fossil fuel industries and critical minerals.
“There are many important geologic issues in Wyoming, and these summaries of 2018 provide residents, elected officials, and state government with a snapshot of energy and mineral resources in Wyoming, as well as the geologic hazards that exist,” said Erin Campbell, state geologist and director of the WSGS, in a statement.