2021 Chignik earthquake

2021 Chignik earthquake
USGS ShakeMap
2021 Chignik earthquake is located in Alaska
Anchorage
Anchorage
Kodiak
Kodiak
Perryville
Perryville
2021 Chignik earthquake
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Interactive map
UTC time2021-07-29 06:15:49
ISC event620857937
USGS-ANSSComCat
Local dateJuly 28, 2021
Local time22:15:49 AKDT (UTC-8)
Magnitude8.2 Mw
Depth32.2 km (20.0 mi)
Epicenter55°28′26″N 157°55′01″W / 55.474°N 157.917°W / 55.474; -157.917
FaultAleutian subduction zone
TypeMegathrust
Areas affectedAlaska
Max. intensityMMI VII (Very strong)
Peak acceleration0.26 g[1]
Tsunami2.62 m (8.6 ft)[2]
Foreshocks7.8 Mw  and 7.6 Mw  in 2020
Aftershocks1,629 (As of 12 July 2022)[3]
Largest 6.9 Mw [4]
CasualtiesNone

An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time.[5] The large megathrust earthquake had a moment magnitude (Mw) of 8.2 according to the United States Geological Survey (USGS).[6] A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled.[7] The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.[8][9][10]

This was the largest earthquake in the United States since the 1965 Rat Islands earthquake, and the 7th largest earthquake in U.S. history.[11] It was also the strongest earthquake globally since the 2015 Illapel earthquake, tying the 2017 Chiapas earthquake and 2018 Fiji earthquake.

No casualties or serious damage were reported in the aftermath of the mainshock, as well as some of the strong aftershocks. In Perryville, the closest populated area to the quake, cracks appeared in drywalls and on the ground. Some homes were also shifted.[12] The limited impact from this earthquake was attributed to it occurring offshore from the sparsely-populated Alaska Peninsula. A tsunami warning was rescinded and no large waves were observed because the earthquake took place 32 km beneath the seafloor; deep enough that vertical uplift of the seafloor was limited therefore displacing smaller amounts of water.[13]

  1. ^ ANSS: Alaska 2021 , Shake Map: PGA (accessed 3 December 2022).
  2. ^ Cite error: The named reference GDACS was invoked but never defined (see the help page).
  3. ^ "Earthquake impact database". United States Geological Survey.
  4. ^ "M 6.9 – 125 km SE of Perryville, Alaska". United States Geological Survey.
  5. ^ "Gulf of Alaska coast under tsunami warning following 8.2 earthquake". Anchorage Daily News. July 29, 2021. Archived from the original on July 30, 2021. Retrieved July 29, 2021.
  6. ^ "M 8.2 – 91 km ESE of Perryville, Alaska". United States Geological Survey. Retrieved July 29, 2021.
  7. ^ "U.S. Tsunami Warning System". U.S. Tsunami Warning System. Retrieved July 29, 2021.
  8. ^ "M 5.9 – 119 km SSE of Chignik, Alaska". United States Geological Survey. Retrieved July 29, 2021.
  9. ^ "M 6.1 – 114 km SSE of Perryville, Alaska". United States Geological Survey. Retrieved July 29, 2021.
  10. ^ "M 6.9 – 117 km SE of Perryville, Alaska". Retrieved August 14, 2021.
  11. ^ "M 8.7 – Rat Islands, Aleutian Islands, Alaska". United States Geological Survey. February 4, 1965. Retrieved July 29, 2021.
  12. ^ Irby, Marlise (August 5, 2021). "State officials assess damage at sites near magnitude 8.2 earthquake on Alaska Peninsula". Alaska's News Source. KTUU-TV. Retrieved October 2, 2021.
  13. ^ Grove, Casey (July 30, 2021). "Listen: Why a major Alaska earthquake triggered warnings but no major damage". KTOO. Alaska Public Media. Retrieved October 2, 2021.