133 km E of Chignik, 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 1,900 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 180,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 7,900× the energy of this one
3. Magna, Utah 2020 M 5.7 5,600× the energy of this one
4. This earthquake M 3.2 about 1,900 lb of TNT
5. Around the size people start to feel M 3.0 this one released 2× 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 since 2016 was M 4.5 on 2017-03-28 — about 89 times the energy of this one.

Before 2016, the USGS record lists 12 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 117 km SSE of Ugashik, Alaska · 37 km NNW of this epicentre May 29, 2015
2. 6.3 112 km E of Chignik, Alaska · 25 km WSW of this epicentre Feb 25, 1953
3. 6.1 132 km E of Chignik, Alaska · 9 km SSW of this epicentre Sep 13, 1911
4. 6.1 118 km ESE of Chignik, Alaska · 45 km SSW of this epicentre Mar 16, 1940
5. 5.4 115 km SSE of Ugashik, Alaska · 41 km N 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 56.2783, -156.2447. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.3 Alaska Peninsula 21:33 UTC
2. 1.6 112 km ENE of Chignik, Alaska 07:38 UTC
3. 2.1 104 km ENE of Chignik, Alaska 16:27 UTC
4. 3.8 121 km WSW of Akhiok, Alaska 05:01 UTC
5. 2.0 128 km SSE of Ugashik, Alaska 23:21 UTC
6. 2.4 119 km E of Chignik, Alaska 17:26 UTC
7. 2.1 123 km E of Chignik, Alaska 21:41 UTC
8. 2.0 107 km E of Chignik, Alaska 03:39 UTC
9. 1.9 116 km SE of Ugashik, Alaska 06:59 UTC
10. 2.0 114 km SSE of Ugashik, Alaska 00:59 UTC
11. 2.9 116 km ESE of Chignik, Alaska 16:17 UTC
12. 2.2 114 km ESE of Chignik, Alaska 17:46 UTC
13. 2.3 124 km E of Chignik, Alaska 16:05 UTC
14. 2.1 118 km E of Chignik, Alaska 03:08 UTC
15. 2.3 120 km SW of Akhiok, Alaska 05:12 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 01:32 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.