M4.0 earthquake 119 km S of Unalaska, Alaska

Monday, October 21, 2024, 03:04:16 UTC · 52.808°N, 166.792°W

A magnitude 4.0 earthquake struck 119 km S of Unalaska, Alaska on Monday, October 21, 2024, 03:04:16 UTC, at a depth of 35.0 km (shallow).

Magnitude: 4.0; Light · mwr
Depth: 35 km; Shallow
Felt reports: 0; Did You Feel It?
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

15 tons of TNT

That is about 1/998 of the Hiroshima bomb. A magnitude 5.0 releases about 32 times more energy.

Tectonic setting

55 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

35 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 8 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.4 on October 21, 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 689 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 13 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 · 275 km away · intensity VI
168 deaths$26 million damagetsunami
1965M6.5
Aleutian Islands: Fox Islands
2 Jul 1965 · 56 km away
Limited damage (under $1M)tsunami
1917M7.9
Alaska Peninsula
31 May 1917 · 268 km away · intensity V
1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 66 km away
1907M7.8
Aleutian Islands
2 Sep 1907 · 199 km away
1929M7.8
Aleutian Islands: Fox Islands
7 Mar 1929 · 298 km away · intensity V
tsunami

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

Nearby trackers