Kodiak Island region, Alaska

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

At this magnitude and depth, people at rest would likely notice it out to about 25 km (16 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 480 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 32,000× the energy of this one
2. Magna, Utah 2020 M 5.7 22,000× the energy of this one
3. Around the size people start to feel M 3.0 2× the energy of this one
4. This earthquake M 2.8 about 480 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 5.4 on 2017-05-11 — about 7,900 times the energy of this one.

Before 2016, the USGS record lists 71 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 100 km SSE of Old Harbor, Alaska · 30 km W of this epicentre Jun 19, 1986
2. 6.6 88 km SSE of Old Harbor, Alaska · 28 km WNW of this epicentre Dec 21, 1917
3. 6.6 94 km SSE of Old Harbor, Alaska · 19 km WNW of this epicentre Apr 12, 1978
4. 6.5 85 km SSE of Old Harbor, Alaska · 38 km WNW of this epicentre Mar 30, 1964
5. 6.4 95 km S of Old Harbor, Alaska · 36 km W of this epicentre Apr 16, 1964

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 56.3461, -152.4221. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 4.6 125 km SSE of Old Harbor, Alaska 19:19 UTC
2. 4.2 142 km SSE of Old Harbor, Alaska 19:18 UTC
3. 3.3 129 km SSE of Old Harbor, Alaska 19:17 UTC
4. 2.4 122 km SSE of Old Harbor, Alaska 19:15 UTC
5. 2.9 102 km SSE of Old Harbor, Alaska 19:12 UTC
6. 4.5 137 km SSE of Old Harbor, Alaska 19:09 UTC
7. 2.9 88 km SSE of Old Harbor, Alaska 18:39 UTC
8. 3.2 133 km SE of Old Harbor, Alaska 18:38 UTC
9. 3.2 113 km SE of Old Harbor, Alaska 17:57 UTC
10. 3.2 124 km SE of Old Harbor, Alaska 15:20 UTC
11. 3.3 127 km SE of Old Harbor, Alaska 13:48 UTC
12. 2.6 120 km SSE of Old Harbor, Alaska 11:57 UTC
13. 4.9 128 km SE of Old Harbor, Alaska 11:45 UTC
14. 2.2 78 km SSE of Old Harbor, Alaska 11:40 UTC
15. 2.8 119 km SE of Old Harbor, Alaska 11:26 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:37 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.