M3.7 earthquake 77 km SW of Unalaska, Alaska

Thursday, April 4, 2024, 19:59:06 UTC · 53.362°N, 167.317°W

A magnitude 3.7 earthquake struck 77 km SW of Unalaska, Alaska on Thursday, April 4, 2024, 19:59:06 UTC, at a depth of 87.1 km (intermediate). USGS received 1 “Did You Feel It?” report, with a maximum reported intensity of III (weak).

Magnitude: 3.7; Minor · mb
Depth: 87 km; Intermediate
Felt reports: 1; Max intensity III
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

5 tons of TNT

That is about 1/2,814 of the Hiroshima bomb. A magnitude 5.0 releases about 89 times more energy.

Tectonic setting

125 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: intermediate

87 km

Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.

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>0.330	III · Weak	1	110 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 7 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.6 on April 10, 2024. 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 696 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 · 297 km away · intensity VI
168 deaths$26 million damagetsunami
1965M6.5
Aleutian Islands: Fox Islands
2 Jul 1965 · 40 km away
Limited damage (under $1M)tsunami
1917M7.9
Alaska Peninsula
31 May 1917 · 198 km away · intensity V
1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 108 km away
1907M7.8
Aleutian Islands
2 Sep 1907 · 183 km away
1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 178 km away

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

Nearby trackers