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Before we get into what happened during the month of December 2021, let’s review what happened at Yellowstone over the past year. 2021 Seismicity Typically, there are 1,500 to 2,500 earthquakes located every year in the Yellowstone region. In 2021, there were 2,773 located earthquakes scattered throughout the Park. Consistent with previous years, most earthquakes were caused by water circulating and interacting with existing faults, which are found throughout the region. There were 27 earthquake swarms in 2021 (earthquakes located in tight clusters during short periods of time). The most noteworthy swarm occurred in mid-July beneath Yellowstone Lake, which included over 800 earthquakes. In 2021, about 65% of the earthquakes were part of swarms. 2021 Deformation The radar interferogram (composed of radar images acquired from satellites) shows us how the ground surface is changing. The colored fringes show changes in the elevation of the ground measured on a fine scale (mm to cm). The
