QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1ml

124 km S of Unalaska, Alaska

Yes. A magnitude 2.1 earthquake was recorded 124 km S of Unalaska, Alaska, at 4:37 pm AKDT on 30 September 2017 (00:37 UTC), 15 km deep.

· 15 km deep · released about 43 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 2.1 (ml)
Depth
15 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1193 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 9 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 43 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.1 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 350,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 250,000× the energy of this one
  3. Around the size people start to feel M 3.0 22× the energy of this one
  4. This earthquake M 2.1 about 43 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 5.9 on 2017-05-24 — about 500,000 times the energy of this one.

Before 2016, the USGS record lists 44 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.5 127 km E of Nikolski, Alaska · 20 km W of this epicentre
  2. 6.4 118 km E of Nikolski, Alaska · 29 km W of this epicentre
  3. 6.4 123 km ESE of Nikolski, Alaska · 33 km WSW of this epicentre
  4. 6.3 136 km ESE of Nikolski, Alaska · 19 km SW of this epicentre
  5. 6.3 Fox Islands, Aleutian Islands, Alaska · 39 km WSW 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 52.7581, -166.7041. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.2 122 km S of Unalaska, Alaska
  2. 2.5 148 km ESE of Nikolski, Alaska
  3. 3.4 80 km SSW of Unalaska, Alaska
  4. 2.4 87 km SSW of Unalaska, Alaska
  5. 1.8 98 km SSW of Unalaska, Alaska
  6. 1.9 96 km S of Unalaska, Alaska
  7. 2.5 90 km SSW of Unalaska, Alaska
  8. 2.1 88 km SSW of Unalaska, Alaska
  9. 1.9 88 km SSW of Unalaska, Alaska
  10. 1.9 88 km SSW of Unalaska, Alaska
  11. 3.6 86 km SSW of Unalaska, Alaska
  12. 3.6 90 km SSW of Unalaska, Alaska
  13. 2.0 80 km S of Unalaska, Alaska
  14. 2.4 82 km S of Unalaska, Alaska
  15. 1.9 117 km S of Unalaska, 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.