Reviewed by USGSAlaska4y ago
M3.5 earthquake 103 km E of Chignik, Alaska
Monday, December 27, 2021, 20:13:12 UTC · 56.445°N, 156.750°W
A magnitude 3.5 earthquake struck 103 km E of Chignik, Alaska on Monday, December 27, 2021, 20:13:12 UTC, at a depth of 2.1 km (shallow).
- Magnitude
- 3.5
- Minor · ml
- Depth
- 2 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- III
- Weak (ShakeMap)
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
3 tons of TNT
That is about 1/5,615 of the Hiroshima bomb. A magnitude 5.0 releases about 178 times more energy.
Tectonic setting
203 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
2 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 M2.8 on January 4, 2022. 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 418 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 · 167 km SW of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 140 km SW of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 191 km SW of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 273 km SW of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 254 km SW of this epicenter
- 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 192 km NE of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 67 km S of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 13 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 212 km away · intensity VIII
Limited damage (under $1M)
- 1788M8.0
Unga Island
21 Jul 1788 · 237 km away · intensity VII
Limited damage (under $1M)tsunami
- 2020M7.8
Alaska
22 Jul 2020 · 191 km away · intensity VII
Limited damage (under $1M)tsunami
- 1970M6.0
Andreanof Islands
11 Mar 1970 · 209 km away · intensity V
Limited damage (under $1M)tsunami
- 1792
Kodiak Island
1792 · 296 km away · intensity VII
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 147 km away · intensity VI
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.