133 km SE of Old Harbor, Alaska

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.

At this magnitude and depth, people at rest would likely notice it out to about 276 km (171 mi) from the epicentre. Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

How big was it?

This earthquake released about 3.8 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.6 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 45× the energy of this one
2. Mineral, Virginia 2011 M 5.8 2× the energy of this one
3. Magna, Utah 2020 M 5.7 1.4× the energy of this one
4. This earthquake M 5.6 about 3.8 kilotons of TNT
5. Around the size people start to feel M 3.0 this one released 7,900× more

Energy from the Gutenberg–Richter relation (log₁₀E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km (31 mi) since our catalogue begins in 2016. The previous largest was M 4.7 on 2019-12-21.

Before 2016, the USGS record lists 49 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 94 km SSE of Old Harbor, Alaska · 48 km WNW of this epicentre Apr 12, 1978
2. 6.3 98 km SE of Old Harbor, Alaska · 35 km NW of this epicentre Apr 12, 1964
3. 6.3 94 km SE of Old Harbor, Alaska · 48 km N of this epicentre Aug 1, 1974
4. 6.2 97 km SSE of Old Harbor, Alaska · 37 km NW of this epicentre May 12, 1964
5. 6.2 129 km SSE of Old Harbor, Alaska · 23 km WSW of this epicentre May 7, 1999

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 56.2482, -151.9738. Map © OpenStreetMap contributors.

Aftershocks so far

45 earthquakes have been recorded within 50 km since this one.

1. 3.3 131 km SSE of Old Harbor, Alaska 20:24 UTC
2. 3.1 128 km SSE of Old Harbor, Alaska 19:08 UTC
3. 2.7 149 km SSE of Old Harbor, Alaska 17:44 UTC
4. 2.5 167 km SSE of Old Harbor, Alaska 15:29 UTC
5. 2.4 153 km SSE of Old Harbor, Alaska 16:18 UTC
6. 3.2 115 km SSE of Old Harbor, Alaska 00:06 UTC
7. 3.3 95 km SSE of Old Harbor, Alaska 01:11 UTC
8. 3.3 108 km SE of Old Harbor, Alaska 16:58 UTC
9. 2.5 168 km SSE of Old Harbor, Alaska 21:22 UTC
10. 3.1 150 km SE of Old Harbor, Alaska 04:03 UTC
11. 3.2 142 km SE of Old Harbor, Alaska 07:52 UTC
12. 3.0 120 km SE of Old Harbor, Alaska 07:42 UTC
13. 4.6 117 km SE of Old Harbor, Alaska 06:35 UTC
14. 3.3 130 km SSE of Old Harbor, Alaska 08:27 UTC
15. 3.5 116 km SSE of Old Harbor, Alaska 12:52 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 22:55 UTC. QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

• The official USGS event page — the source of record for every value above
• Did you feel it? Report it to USGS — reports go to USGS, not to us
• ShakeMap for this event, when USGS has produced one

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.