Earthquake near Sand Point, AK

A magnitude 3.8 earthquake was recorded 28 km (18 mi) E of Sand Point, AK, at 1:37 am AKDT on 20 September 2017 (09:37 UTC). This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

How big was it?

This earthquake released about 7.6 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.8 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 22,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 1,000× the energy of this one
3. Magna, Utah 2020 M 5.7 710× the energy of this one
4. This earthquake M 3.8 about 7.6 tons of TNT
5. Around the size people start to feel M 3.0 this one released 16× 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

No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.

Before 2016, the USGS record lists 20 earthquakes of M5 or more within 50 km; the five largest:

1. 7.4 54 km SE of Sand Point, Alaska · 40 km SSE of this epicentre May 31, 1917
2. 6.9 17 km S of Sand Point, Alaska · 31 km SW of this epicentre May 13, 1993
3. 6.3 68 km SE of Sand Point, Alaska · 48 km SSE of this epicentre Oct 30, 1932
4. 6.2 35 km S of Sand Point, Alaska · 46 km SW of this epicentre May 25, 1993
5. 6.0 54 km E of Sand Point, Alaska · 26 km E of this epicentre Oct 3, 1916

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 55.3371, -160.0541. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.7 47 km E of Sand Point, Alaska 13:10 UTC
2. 2.3 63 km ESE of Sand Point, Alaska 14:33 UTC
3. 3.2 68 km ESE of Sand Point, Alaska 01:05 UTC
4. 2.7 47 km ENE of Sand Point, Alaska 18:30 UTC
5. 2.1 64 km ESE of Sand Point, Alaska 00:15 UTC
6. 2.4 27 km ENE of Sand Point, Alaska 19:10 UTC
7. 3.4 63 km ESE of Sand Point, Alaska 20:31 UTC
8. 1.9 48 km SE of Sand Point, Alaska 16:45 UTC
9. 2.8 46 km SSW of Ivanof Bay, Alaska 00:23 UTC
10. 1.9 14 km N of Sand Point, Alaska 18:35 UTC
11. 1.9 48 km SSE of Sand Point, Alaska 07:04 UTC
12. 2.0 21 km S of Sand Point, Alaska 05:56 UTC
13. 2.1 49 km SE of Sand Point, Alaska 00:45 UTC
14. 1.6 68 km ESE of Sand Point, Alaska 10:59 UTC
15. 2.1 38 km ESE of Sand Point, Alaska 14:25 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 02:05 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.