104 km SSE of Old Harbor, 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 10 km (6 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 170 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 89,000× the energy of this one
2. Magna, Utah 2020 M 5.7 63,000× the energy of this one
3. Around the size people start to feel M 3.0 5.6× the energy of this one
4. This earthquake M 2.5 about 170 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 5.2 on 2020-04-17 — about 11,000 times the energy of this one.

Before 2016, the USGS record lists 84 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 100 km SSE of Old Harbor, Alaska · 9 km WNW of this epicentre Jun 19, 1986
2. 6.6 88 km SSE of Old Harbor, Alaska · 16 km NNW of this epicentre Dec 21, 1917
3. 6.6 94 km SSE of Old Harbor, Alaska · 14 km NNE of this epicentre Apr 12, 1978
4. 6.5 85 km SSE of Old Harbor, Alaska · 22 km NW of this epicentre Mar 30, 1964
5. 6.5 95 km SSE of Akhiok, Alaska · 40 km WSW of this epicentre Sep 12, 1986

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 56.3050, -152.7820. Map © OpenStreetMap contributors.

Aftershocks so far

2 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

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 16:38 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.