M5.1 earthquake 70 km S of Unalaska, Alaska

Tuesday, February 22, 2022, 04:10:04 UTC · 53.246°N, 166.697°W

A magnitude 5.1 earthquake struck 70 km S of Unalaska, Alaska on Tuesday, February 22, 2022, 04:10:04 UTC, at a depth of 43.5 km (shallow). USGS received 2 “Did You Feel It?” reports, with a maximum reported intensity of IV (light). It is the strongest earthquake within 300 km since an M5.1 on February 21, 2022.

Magnitude: 5.1; Moderate · mb
Depth: 43 km; Shallow
Felt reports: 2; Max intensity IV
Est. shaking: III; Weak (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 75 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

674 tons of TNT

That is about 1/22 of the Hiroshima bomb. It released about 1 times the energy of a magnitude 5.0.

Tectonic setting

96 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

43 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
99685<br>0.320	III · Weak	2	77 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 75 km

USGS lists 14 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M4.5 on February 28, 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 669 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 12 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 168 recorded deaths. The most severe:

1946M8.6
Unimak Island
1 Apr 1946 · 258 km away · intensity VI
168 deaths$26 million damagetsunami
1965M6.5
Aleutian Islands: Fox Islands
2 Jul 1965 · 62 km away
Limited damage (under $1M)tsunami
1917M7.9
Alaska Peninsula
31 May 1917 · 233 km away · intensity V
1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 108 km away
1907M7.8
Aleutian Islands
2 Sep 1907 · 216 km away
1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 220 km away

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

Nearby trackers