M3.9 earthquake 145 km SSE of Perryville, Alaska

Saturday, December 25, 2021, 23:10:13 UTC · 54.816°N, 157.898°W

A magnitude 3.9 earthquake struck 145 km SSE of Perryville, Alaska on Saturday, December 25, 2021, 23:10:13 UTC, at a depth of 5.3 km (shallow). USGS received 1 “Did You Feel It?” report, with a maximum reported intensity of II (weak).

Magnitude: 3.9; Minor · ml
Depth: 5 km; Shallow
Felt reports: 1; Max intensity II
Est. shaking: I; Not felt (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

71 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

5 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
99501<br>0.330	II · Weak	1	864 km

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 6 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.2 on January 6, 2022. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 302 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

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:

2020M7.8
Alaska
22 Jul 2020 · 53 km away · intensity VII
Limited damage (under $1M)tsunami
1938M8.2
Alaska
10 Nov 1938 · 80 km away · intensity VI
tsunami
2021M8.2
Alaska Peninsula
29 Jul 2021 · 57 km away · intensity VIII
tsunami
1788M8.0
Alaska Peninsula
6 Aug 1788 · 199 km away
tsunami
2020M7.6
Alaska
19 Oct 2020 · 114 km away · intensity IX
tsunami
1948M7.5
Alaska Peninsula
14 May 1948 · 203 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers