Description: From Orr and others, 2024: "On December 7, 2021, at 15:33 HAST (December 8 at 01:33 UTC), an earthquake swarm occurred 7.5 km north of Davidof volcano. During the first few days of the swarm, several energetic earthquake bursts took place, the largest of which was a ML 4.2 on December 10. The sudden increase in seismic activity was uncharacteristic of the area, prompting AVO to raise the Aviation Color Code and Volcano Alert Level from UNASSIGNED to YELLOW and ADVISORY on December 10 in anticipation of possible volcanic activity.
"Seismicity waned gradually over the next week and the swarm seemingly ceased on December 20. The hypocenters of earthquakes from the swarm formed a northeast-southwest trending lineation north of the volcano. However, this linear trend is interpreted to be an artifact because the earthquakes were located outside the regional network-the closest seismic stations are the four on Little Sitkin Island, ~12 km [~7 mi] east of Davidof volcano. The earthquakes occurred at a variety of depths, the deepest of which was 9.8 km [6.1 mi] below sea level. Notably, the swarm produced 2 earthquakes of ML >4 and 13 earthquakes of ML >3. On December 29, more than one week after the swarm ended, AVO lowered the Aviation Color Code and Volcano Alert Level of Davidof volcano to UNASSIGNED."
AVO raised Davidof to YELLOW/ADVISORY again on January 26, 2022, stating "over the past two days a swarm of earthquakes has occurred in the vicinity of Davidof volcano. The largest earthquake in the current sequence happened yesterday at 4:02 PM AKST (January 26, 01:02 UTC) and had a magnitude of 4.9. A similar earthquake swarm occurred in December 2021. No signs of unrest have been observed in recent satellite images of the volcano."
Elevated seismic activity continued for a few months, occasionally including earthquakes of ML = 3. Afterwards, seismicity gradually declined, and AVO lowered the alert levels to UNASSIGNED on April 22, 2022.