The eastern Brooks Range Swarm kicked into high gear in the summer of 2018. The activity subsided during winter and spring, but picked up again in late summer and early fall of 2019. The cause of this intriguing seasonal shift is unknown. We recorded a total of 1,686 earthquakes within this swarm in 2019, with magnitudes ranging between 0.6 and 3.5. While the activity level was not as high as in 2018, it still remained above the background level as of the end of 2019. The eastern Brooks Range swarm is unusually large, covering an area about 40 miles by 60 miles (70 km by 100 km), about three times the size of other known swarms in Alaska.

The grey dots are historical background seismicity. The red dots show 2019 seismicity.