Reviewed by USGSAlaska5y ago
M3.0 earthquake 122 km SE of Chignik, Alaska
Wednesday, October 20, 2021, 14:32:21 UTC · 55.605°N, 156.873°W
A magnitude 3.0 earthquake struck 122 km SE of Chignik, Alaska on Wednesday, October 20, 2021, 14:32:21 UTC, at a depth of 8.7 km (shallow).
- Magnitude
- 3.0
- Minor · ml
- Depth
- 9 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
477 kg of TNT
That is about 1/31,575 of the Hiroshima bomb. A magnitude 5.0 releases about 1,000 times more energy.
Tectonic setting
127 km
from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.
Depth: shallow
9 km
Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.
I felt it — report to USGS ↗USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.
After the main event
Aftershocks within 50 km
USGS lists 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M2.7 on November 11, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 379 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 95 km SW of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 69 km W of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 124 km SW of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 208 km SW of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 202 km W of this epicenter
- 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 295 km W of this epicenter
- 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 268 km NE of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 27 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 14 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 266 km away · intensity VIII
Limited damage (under $1M)
- 1788M8.0
Unga Island
21 Jul 1788 · 285 km away · intensity VII
Limited damage (under $1M)tsunami
- 2020M7.8
Alaska
22 Jul 2020 · 124 km away · intensity VII
Limited damage (under $1M)tsunami
- 1970M6.0
Andreanof Islands
11 Mar 1970 · 279 km away · intensity V
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 95 km away · intensity VI
tsunami
- 2021M8.2
Alaska Peninsula
29 Jul 2021 · 68 km away · intensity VIII
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.