Quick Quake Briefing: Alaska M8.2 Offshore Earthquake of July 28, 2021

September 23, 2021, 12:00-1:00 PT 

AK QQB imageThe EERI Northern California Regional Chapter and the EERI Learning from Earthquakes Program held a FREE webinar on the M8.2 earthquake that struck on July 28, 2021 (local date) offshore Alaska. The very strong quake was one of the largest to strike Alaska in recent history. It was located about 70 miles east southeast of Perryville, Alaska (about 500 miles southwest of Anchorage). The quake was a result of thrust faulting at a depth of 22 miles on the subduction zone between the Pacific plate and North American plate where the Pacific plate begins diving under Alaska. Fortunately, Alaska was mostly unscathed, thanks to the remote location and depth of the epicenter. Tsunami alerts were issued shortly after the earthquake and several coastal communities were evacuated. Only small tsunami waves measuring under a foot above tide level were observed initially, and tsunami alerts were called off under two hours after the quake. Final maximum wave amplitudes observed were between 1 and 2 feet above the tide, and the tsunami was detected down the U.S. West Coast as well as in Hawaii.

The Quick Quake Briefing featured two speakers from Alaska:

  • Dr. Michael West, State Seismologist, Fairbanks, Alaska. He presented on the seismological mechanism of the earthquake, its relation to other recent earthquakes, and how it influences our thinking about future quakes.
  • Dr. Summer Ohlendorf, Science Officer, NOAA/NWS/ National Tsunami Warning Center, Palmer, Alaska. She presented on the tsunami warning process following this quake, and the evolution of our understanding about the tsunami that was generated.