QuakeIndex

Earthquake · reviewed by a seismologist

M 1.9ml

south of Alaska

Yes. A magnitude 1.9 earthquake was recorded south of Alaska, at 10:51 am AKDT on 25 August 2021 (18:51 UTC), 13 km deep.

· 13 km deep · released about 21 lb of TNT

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Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
Magnitude
M 1.9 (ml)
Depth
13 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1890 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 6 km (4 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 21 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.9 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 710,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 500,000× the energy of this one
  3. Around the size people start to feel M 3.0 45× the energy of this one
  4. This earthquake M 1.9 about 21 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 7.6 on 2020-10-19 — about 350,000,000 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 85 km SE of Sand Point, Alaska · 45 km NNE of this epicentre
  2. 6.1 79 km SE of Sand Point, Alaska · 40 km NNE of this epicentre
  3. 6.0 71 km SSE of Sand Point, Alaska · 41 km N of this epicentre
  4. 5.9 113 km SE of Sand Point, Alaska · 50 km ENE of this epicentre
  5. 5.9 99 km SE of Sand Point, Alaska · 36 km NE of this epicentre

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 54.4005, -159.9145. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 1.8 100 km SSE of Sand Point, Alaska
  2. 2.3 91 km SSE of Sand Point, Alaska
  3. 2.0 100 km SSE of Sand Point, Alaska
  4. 1.9 110 km SSE of Sand Point, Alaska
  5. 1.9 92 km SSE of Sand Point, Alaska
  6. 1.8 124 km SSE of Sand Point, Alaska
  7. 1.9 99 km SSE of Sand Point, Alaska
  8. 2.1 91 km SSE of Sand Point, Alaska
  9. 2.0 112 km SSE of Sand Point, Alaska
  10. 2.7 111 km SE of Sand Point, Alaska
  11. 2.1 112 km SE of Sand Point, Alaska
  12. 2.0 96 km SSE of Sand Point, Alaska
  13. 2.0 105 km SSE of Sand Point, Alaska
  14. 2.0 101 km SSE of Sand Point, Alaska
  15. 2.2 112 km SE of Sand Point, Alaska

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.