116 km SSE of Ugashik, Alaska

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth it was probably too small to be felt, even directly above it. 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 lb of TNT

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 since 2016 was M 4.5 on 2017-03-28 — about 180 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 117 km SSE of Ugashik, Alaska · 2 km ESE of this epicentre May 29, 2015
2. 6.4 104 km SSE of Ugashik, Alaska · 17 km WNW of this epicentre May 20, 1979
3. 6.3 112 km E of Chignik, Alaska · 47 km SSW of this epicentre Feb 25, 1953
4. 6.1 132 km E of Chignik, Alaska · 46 km SSE of this epicentre Sep 13, 1911
5. 5.4 115 km SSE of Ugashik, Alaska · 7 km NE of this epicentre Jun 9, 1971

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 56.6023, -156.4546. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.9 125 km SSE of Ugashik, Alaska 12:30 UTC
2. 1.8 117 km ENE of Chignik, Alaska 15:41 UTC
3. 2.2 135 km SW of Akhiok, Alaska 00:31 UTC
4. 1.5 93 km SE of Ugashik, Alaska 07:22 UTC
5. 2.2 127 km E of Chignik, Alaska 11:25 UTC
6. 2.8 113 km E of Chignik, Alaska 02:03 UTC
7. 2.0 108 km SE of Ugashik, Alaska 01:08 UTC
8. 1.7 81 km SSE of Ugashik, Alaska 04:03 UTC
9. 2.0 95 km E of Chignik, Alaska 07:50 UTC
10. 2.4 82 km SSE of Ugashik, Alaska 01:33 UTC
11. 2.3 119 km SSE of Ugashik, Alaska 02:48 UTC
12. 1.8 103 km SE of Ugashik, Alaska 17:13 UTC
13. 2.1 104 km SSE of Ugashik, Alaska 19:13 UTC
14. 1.9 104 km SE of Ugashik, Alaska 14:44 UTC
15. 2.3 121 km WSW of Akhiok, Alaska 04:42 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 00:58 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.