QuakeIndex

Earthquake · reviewed by a seismologist

M 4.8mwr

61 km SE of Unalaska, Alaska

Yes. A magnitude 4.8 earthquake was recorded 61 km SE of Unalaska, Alaska, at 3:27 pm AKDT on 27 September 2019 (23:27 UTC), 35 km deep. 4 people have reported feeling it to USGS.

· 35 km deep · released about 240 tons 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 4.8 (mwr)
Depth
35 km below the surface
Felt
4 reports · strongest reported intensity III
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 326 days ago

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 167 km (104 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 240 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.8 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 710× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 32× the energy of this one
  3. Magna, Utah 2020 M 5.7 22× the energy of this one
  4. This earthquake M 4.8 about 240 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 500× 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

Tied for the largest within 50 km (31 mi) since 2016, with M 4.8 on 2016-09-18.

Before 2016, the USGS record lists 30 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.1 39 km S of Akutan, Alaska · 36 km NNE of this epicentre
  2. 6.2 57 km SE of Unalaska, Alaska · 7 km NNE of this epicentre
  3. 6.2 36 km ESE of Unalaska, Alaska · 29 km NNW of this epicentre
  4. 6.2 53 km S of Akutan, Alaska · 28 km NE of this epicentre
  5. 6.1 90 km SE of Unalaska, Alaska · 30 km SSE 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 53.4682, -165.9070. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.9 69 km SE of Unalaska, Alaska
  2. 3.8 48 km S of Akutan, Alaska
  3. 2.7 70 km SE of Unalaska, Alaska
  4. 2.0 75 km SE of Unalaska, Alaska
  5. 3.6 77 km SSE of Unalaska, Alaska
  6. 2.8 80 km SE of Unalaska, Alaska
  7. 2.0 32 km SSE of Akutan, Alaska
  8. 2.9 56 km SSE of Unalaska, Alaska
  9. 2.1 77 km S of Akutan, Alaska
  10. 2.2 71 km SE of Unalaska, Alaska
  11. 2.2 107 km SE of Unalaska, Alaska
  12. 2.9 52 km SSE of Akutan, Alaska
  13. 2.3 25 km SSW of Akutan, Alaska
  14. 2.1 82 km SSE of Unalaska, Alaska
  15. 1.7 76 km SSE of Akutan, 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.