Reviewed by USGSAlaska5y ago
M3.9 earthquake 201 km SE of Chignik, Alaska
Wednesday, October 13, 2021, 11:34:21 UTC · 54.913°N, 156.226°W
A magnitude 3.9 earthquake struck 201 km SE of Chignik, Alaska on Wednesday, October 13, 2021, 11:34:21 UTC, at a depth of 4.1 km (shallow). USGS received 1 “Did You Feel It?” report, with a maximum reported intensity of I (not felt).
- Magnitude
- 3.9
- Minor · ml
- Depth
- 4 km
- Shallow
- Felt reports
- 1
- Max intensity I
- Est. shaking
- II
- 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
11 tons of TNT
That is about 1/1,410 of the Hiroshima bomb. A magnitude 5.0 releases about 45 times more energy.
Tectonic setting
41 km
from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
4 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
1 people reported feeling this earthquake to USGS; a per-place breakdown is not available 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 2 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.0 on November 1, 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 334 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 · 128 km W of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 117 km NW of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 152 km W of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 221 km W of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 234 km W of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 109 km N of this epicenter
- 7.026 km SSE of Karluk, AlaskaDecember 6, 1999 · 294 km NE of this epicenter
- 7.0164 km SE of Chignik, AlaskaSeptember 4, 1989 · 47 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 9 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 296 km away · intensity VIII
Limited damage (under $1M)
- 2020M7.8
Alaska
22 Jul 2020 · 152 km away · intensity VII
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 150 km away · intensity VI
tsunami
- 2021M8.2
Alaska Peninsula
29 Jul 2021 · 112 km away · intensity VIII
tsunami
- 1906M7.6
Aleutian Islands
23 Dec 1906 · 260 km away
- 2020M7.6
Alaska
19 Oct 2020 · 221 km away · intensity IX
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.