Earthquake.now

M4.0 Earthquake near Unalaska, United States — 21 January 2025, 17:58 UTC

A light earthquake of magnitude 4.0 was recorded near Unalaska, United States on , with an epicentre 118 km south of Unalaska, at a focal depth of 3.8 km. It ranked as the 13th strongest of 6286 earthquakes recorded in the United States in the preceding 30 days.

4.0 Light

Time (UTC): 2025-01-21 17:58:07

Time (your timezone): —

Magnitude: 4.0 (light)

Focal depth: 3.8 km (shallow)

Epicentre: 52.8221, -166.7600

Location: 118 km S of Unalaska, Alaska

Country: United States

USGS link to NOAA tsunami information: Not linked

Review status: Reviewed

Source: USGS event page

How strong was this earthquake?

Light earthquakes are widely felt near the epicentre and can rattle windows, dishes and hanging objects. Damage is uncommon and usually limited to cracked plaster or fallen loose items.

A magnitude 4.0 earthquake radiates roughly 15 tons of TNT equivalent in seismic energy.

The USGS assigns this earthquake a significance score of 246, which is below the USGS threshold of more than 600 for its significant-earthquake list. The ranking combines magnitude with available Did You Feel It responses and PAGER alert level; it is not a direct measurement of damage.

What the magnitude scale actually measures →

When it happened locally

That is about 06:51 local solar time at the epicentre, around dawn.

This event was shallower than 66% of the 156,095 earthquakes recorded in the United States in our catalogue and stronger than 99% of them.

Where was the epicentre?

The epicentre was located at 52.8221, -166.7600 — 118 km south of Unalaska. The closest other recorded event was a magnitude 2.6 earthquake 27 km east-northeast of here on 31 August 2026.

The nearest other settlements in our records are Dutch Harbor (80 km north-northwest) and Akutan (133 km east-northeast).

Why the 4 km depth matters

At 4 km this was a shallow earthquake. Shallow events release their energy close to the surface, so for a given magnitude they produce noticeably stronger shaking — and more damage — than deeper ones. Roughly three quarters of all earthquakes worldwide occur at shallow depths.

This catalogue does not ingest eyewitness responses, so it cannot confirm where this earthquake was felt. Based on magnitude alone, an event this size is often felt across the surrounding area. Its shallow focus makes stronger surface shaking more likely than for a deeper event of the same magnitude.

Read more on how focal depth changes what you feel →

What does the tsunami information flag mean?

The USGS record does not carry a link to NOAA tsunami information. That field is not an all-clear and does not state whether a tsunami occurred. In this case, a damaging tsunami would be less likely because at M4.0 it falls below the magnitude 6.5 threshold that generally applies before a submarine earthquake displaces enough water to generate a damaging tsunami; it occurred inland rather than beneath the sea floor. For an active coastal alert, use tsunami.gov or your local warning authority.

How earthquakes generate tsunamis, and what the alert levels mean →

Aftershocks and local seismic history

7 further earthquakes have been recorded within about 150 km of the epicentre in the seven days after this event, the largest of them magnitude 5.6.

43 earthquakes of magnitude 4 or above have been logged within roughly 200 km of this epicentre in our catalogue. The strongest was a magnitude 5.6 event near Unalaska on 26 January 2025. This M4.0 event released about 251 times less energy than that event.

14 earthquakes have been recorded within 100 km of this epicentre in the past year, 6 of them in the past 30 days.

How long aftershock sequences last, and how large they get →

Where this event sits in the record

This earthquake is part of the January 2025 worldwide record, and of earthquakes in the United States during January 2025. Browse the full monthly archive to compare periods.

Nearest recorded earthquakes to this epicentre

Other recent earthquakes in the United States

All recorded earthquakes in the United States →

Other magnitude 4 earthquakes worldwide

All magnitude 4 earthquakes →

Questions about this earthquake

How strong was the earthquake near Unalaska?

It measured magnitude 4.0 — a light earthquake. A magnitude 4.0 earthquake radiates roughly 15 tons of TNT equivalent in seismic energy.

How deep was the earthquake near Unalaska?

The focus was 4 km below the surface, which counts as shallow.

Was the Unalaska earthquake felt at the surface?

At magnitude 4.0 and a focal depth of 4 km, shaking would have been concentrated near the epicentre.

When did the earthquake near Unalaska happen?

21 January 2025 at 17:58 UTC.

Was there a tsunami?

No. The USGS record carries no tsunami-information link for this event.

Have there been aftershocks?

7 further earthquakes have been recorded within about 150 km of the epicentre in the seven days after this event, the largest of them magnitude 5.6.

How often do earthquakes happen near Unalaska?

43 earthquakes of magnitude 4 or above have been logged within roughly 200 km of this epicentre in our catalogue. The strongest was a magnitude 5.6 event near Unalaska on 26 January 2025. This M4.0 event released about 251 times less energy than that event.