October 2020 Alaska Peninsula earthquake
  | |
| UTC time | 2020-10-19 20:54:40 |
|---|---|
| ISC event | 619498906 |
| USGS-ANSS | ComCat |
| Local date | October 19, 2020 |
| Local time | 12:54 pm |
| Magnitude | 7.6 Mw |
| Depth | 29.1 km |
| Epicenter | 54°39′43″N 159°40′30″W / 54.662°N 159.675°W |
| Type | Strike-slip |
| Areas affected | Alaska, United States |
| Max. intensity | VIII (Severe) |
| Tsunami | Yes (2.5 ft) |
| Aftershocks | 167 (as of 2020-10-26) Largest: Mw 5.9 14:45 UTC, 19 Oct 2020 |
| Casualties | 0 |
The October 2020 Simeonof earthquake was a magnitude 7.6 earthquake that struck 97 km south southeast from the city of Sand Point, Alaska. It came almost three months after a magnitude 7.8 struck the same region.[1] This earthquake is considered an aftershock of the July event.[2] No damage was reported immediately following the earthquake.[3][4]
It is the third largest earthquake in 2020 so far.
Tectonic setting
Off the coast of Alaska lies the Aleutian Subduction Zone–a 2,500 mile long convergent plate boundary where the Pacific Plate subducts under the North American Plate at a rate of 6–7 cm/yr. This megathrust fault has been the source of many large earthquakes including the 1964 Alaskan earthquake that registered a magnitude 9.2 and remains the second largest earthquake in recorded history.
Earthquake
This earthquake occurred along a north northwest striking strike-slip fault rather than the thrust mechanism seen in the July event.[5][6] It did not occur along the megathrust boundary but within one of the two interacting plates. Maximum slip along the fault is estimated at 3.4 meters.[5]
As for the July 22 thrust earthquake, that event occurred on the Shumagin Gap; an area on the Aleutian Megathrust which has not slipped for decades.[7] That section of the megathrust was previously thought to experience slow creep as no earthquakes have been seen on the gap for a century, while the recurrence interval for megathrust events there is 50 to 90 years. It is situated between the rupture zone of the 1946 and 1938 earthquake. This event appears to only unlock the deeper part of the fault, with the shallow portion still capable of generating a large tsunami.[8] In addition, the slip generated by the earthquake is small for its size, with the potential for large earthquakes again in the future.[9]
Tsunami
A tsunami warning was issued but was later downgraded to an advisory.[10] A wave was measured at 2.3 ft. (70.1 cm) at Sand Point.[11] At King Cove, the tsunami had a wave height of 2.1 ft. (64.0 cm) and was 2.5 ft. at Chignik Bay.[12][13] As of 7:05 pm (AKDT), the tsunami alert is at Advisory level. In the state of Hawaii, alert level Advisory was issued at 5:55 pm.[14] Wave heights ranging between 0.1-1.2 ft (2–38 cm) were detected along the islands.[15] Tsunami warning was later cancelled at 05:05:15 (UTC).[16]
Aftershocks
As of 2020-10-26, there has been 167 recorded aftershocks, including nine that registered greater than Mw 5.0. The largest was an Mw 5.9 on October 19.[17] Other large aftershocks include an Mw 5.8, 5.7, 5.6 and 5.5.[18][19][20][21]
See also
References
- ^ "M 7.8 - 99 km SSE of Perryville, Alaska". US Geological Survey.
- ^ "M 7.6 - 97 km SSE of Sand Point, Alaska". earthquake.usgs.gov. Retrieved 2020-10-19.
- ^ "Tsunami warning cancelled following 7.5 magnitude earthquake off Alaska Peninsula". Anchorage Daily News. October 19, 2020. Retrieved October 19, 2020.
- ^ Magnitude 7.5 Earthquake Hits Alaskan Peninsula - Oct. 19, 2020
- ^ a b "Finite Fault". US Geological Survey.
- ^ "Significant Earthquake Information ALASKA". NGDC. Retrieved 21 December 2020.
- ^ Gardine, Matt (3 August 2017). "A NEW PERSPECTIVE ON SEISMIC HAZARDS IN THE SHUMAGIN GAP". Alaska Earthquake Center.
- ^ Nadin, E (1 August 2020). "Does Alaska's magnitude-7.8 Simeonof earthquake finally close a seismic gap?". Temblor.
- ^ Chengli Liu, Thorne Lay, Xiong Xiong, Yangmao Wen (29 October 2020). "Rupture of the 2020 MW 7.8 Earthquake in the Shumagin Gap Inferred From Seismic and Geodetic Observations". Geophysical Research Letters. 47 – via AGU.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Service, National Weather. "National Weather Service - Tsunami Hazards". www.tsunami.gov. Retrieved 2020-10-19.
- ^ "Public Tsunami Message Number 6". NOAA.
- ^ "Public Tsunami Message Number 11". NOAA.
- ^ "Tsunami Event Information SHUMAGIN ISLANDS, AK". NGDC. Retrieved 21 December 2020.
- ^ MARTINEZ, PETER (20 October 2020). "7.5 magnitude earthquake strikes near Alaska, triggering tsunami advisory". CBS News.
- ^ "Message: Hawaii Warn/Adv./Watch #3". NOAA.
- ^ "Message: AK/BC/US West Coast Warn/Adv./Watch #13". NOAA.
- ^ "M 5.9 - 107 km SSE of Sand Point, Alaska". US Geological Survey.
- ^ "M 5.8 - 115 km SSE of Sand Point, Alaska". US Geological Survey.
- ^ "M 5.7 - 92 km SE of Sand Point, Alaska". US Geological Survey.
- ^ "M 5.6 - 126 km SSE of Sand Point, Alaska". US Geology Survey.
- ^ "M 5.5 - 133 km SSE of Sand Point, Alaska". US Geology Survey.