2021 Chignik earthquake: Difference between revisions
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| magnitude = 8.2 {{M|w|link=yes}} |
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| image = 2021-07-29 Perryville, Alaska M8.2 earthquake shakemap (USGS).jpg |
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| local-time = 22:15:49 |
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Revision as of 09:56, 29 July 2021
 | This article is about a current disaster where information can change quickly or be unreliable. The latest page updates may not reflect the most up-to-date information. |
.jpg) | |
  Anchorage Kodiak Perryville  | |
| UTC time | 2021-07-29 06:15:49 |
|---|---|
| USGS-ANSS | ComCat |
| Local date | July 28, 2021 |
| Local time | 22:15:49 |
| Magnitude | 8.2 Mw |
| Depth | 32.2 km (20.0 mi) |
| Epicenter | 55°28′26″N 157°55′01″W / 55.474°N 157.917°W |
| Fault | Aleutian subduction zone |
| Type | Megathrust |
| Areas affected | Alaska |
| Max. intensity | MMI VII (Very strong)[1] |
| Tsunami | Yes |
| Foreshocks | M 7.8 & M 7.6 in 2020 |
| Aftershocks | Multiple. Strongest so far is a 6.1 Mw |
An earthquake occurred off the coast of the Alaska Peninsula on July 28 at 10:15 p.m. local time.[2] The large thrust earthquake had a moment magnitude (Mw) of 8.2 according to the United States Geological Survey (USGS).[1] A tsunami warning issued by the National Oceanic and Atmospheric Administration (NOAA) is in effect as of July 29 at 06:21:23 AM UTC.[3] It is the largest earthquake in the United States since the 1965 Rat Islands earthquake.
The same region was struck by a magnitude 7.8 earthquake on July 22, 2020, and another 7.6 earthquake on October of the same year, with the USGS confirming that these quakes were foreshocks.[4][5][1]
The mainshock was followed by a number of aftershocks, including two that were of magnitude 5.9 and 6.1, respectively.[6][7]
Tectonic setting
The Aleutian Islands lie near a convergent plate boundary where the Pacific Plate meets the North American Plate. The location where the plates converge is marked on the ocean floor by the Aleutian Trench. The Pacific Plate dives beneath the North American Plate along the Aleutian subduction zone which extends for approximately 4,000 km. The subduction zone is a large thrust fault capable of generating large megathrust earthquakes, sometimes tsunamigenic. The 1946 Aleutian Islands earthquake and 1964 Alaska earthquake, measuring 8.6 Mw and 9.2 Mw respectively.[8][9]
Earthquake
Occurring southeast of Perryville, Alaska (south of the Alaska Peninsula), the earthquake happened as the result of thrust faulting on or near the subduction zone interface between the Pacific and North America plates. The preliminary focal mechanism solution indicates rupture occurred on a fault dipping either shallowly to the northwest, or steeply to the southeast. The location, mechanism and depth – and the large size of the event – are all consistent with slip occurring on the subduction zone interface between the two plates. At the location of this event, the Pacific plate converges with North America to the northwest at a rate of about 64 mm/yr, subducting at the Alaska-Aleutians trench ~125 km to the southeast of the earthquake.
Tsunami
The maximum tsunami height of 0.7 feet or 21.3 centimeters was recorded in the city of Old Harbour in the Kodiak Island Borough on Kodiak Island.[10] The city of Sand Point in the Aleutians East Borough on Popof Island recorded a tsunami height of 0.5 feet or 15.2 centimeters.[10] A tsunami height of 0.5 feet or 15.2 centimeters was also recorded in the city Kodiak in the Kodiak Island Borough on Kodiak Island.[11] A tsunami height of 0.4 feet or 12.2 centimeters was recorded in the city of King Cove in the Aleutians East Borough on Deer Island (Aleutian Islands).[11]
See also
- List of earthquakes in 2021
- List of megathrust earthquakes
- List of earthquakes in Alaska
- List of earthquakes in the United States
References
- ^ a b c "M 8.2 – 91 km ESE of Perryville, Alaska". earthquake.usgs.gov. USGS. Retrieved July 29, 2021.
- ^ "Gulf of Alaska coast under tsunami warning following 8.2 earthquake". Anchorage Daily News. July 29, 2021. Retrieved July 29, 2021.
- ^ "U.S. Tsunami Warning System". tsunami.gov. NOAA National Centers for Environmental Information. Retrieved July 29, 2021.
- ^ "M 7.8 – 99 km SSE of Perryville, Alaska". earthquake.usgs.gov. USGS. Retrieved July 29, 2021.
- ^ "M 7.6 – 99 km SE of Sand Point, Alaska". earthquake.usgs.gov. USGS. Retrieved July 29, 2021.
- ^ "M 5.9 – 119 km SSE of Chignik, Alaska". earthquake.usgs.gov. USGS. Retrieved July 29, 2021.
- ^ "M 6.1 – 114 km SSE of Perryville, Alaska". earthquake.usgs.gov. USGS. Retrieved July 29, 2021.
- ^ "M 8.6 - 1946 Aleutian Islands (Unimak Island) Earthquake, Alaska". earthquake.usgs.gov. USGS. Retrieved July 9, 2021.
- ^ "M 9.2 - 1964 Prince William Sound Earthquake, Alaska". earthquake.usgs.gov. USGS. Retrieved July 9, 2021.
- ^ a b "Public Tsunami Message Number 5". tsunami.gov. Palmer, Alaska: NWS National Tsunami Warning Center. July 29, 2021. Retrieved July 29, 2021.
- ^ a b "Public Tsunami Message Number 6". tsunami.gov. Palmer, Alaska: NWS National Tsunami Warning Center. July 29, 2021. Retrieved July 29, 2021.