QuakeIndex

Earthquake · reviewed by a seismologist

M 3.8ml

56 km SW of Tatitlek, Alaska

Yes. A magnitude 3.8 earthquake was recorded 56 km SW of Tatitlek, Alaska, at 9:43 pm AKDT on 21 August 2018 (05:43 UTC), 6.9 km deep. 6 people have reported feeling it to USGS.

· 6.9 km deep · released about 7.6 tons of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Chugach Census Area 64 km
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 3.8 (ml)
Depth
6.9 km below the surface
Felt
6 reports · strongest reported intensity IV
Measured shaking
intensity IV (ShakeMap)
Nearest
Chugach Census Area, 64 km E
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1185 days ago

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 82 km (51 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 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

The largest earthquake within 50 km since 2016 was M 5.3 on 2017-11-27 — about 180 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 9.2 The 1964 Prince William Sound, Alaska Earthquake · 48 km N of this epicentre
  2. 7.0 52 km NE of Chenega, Alaska · 12 km SSE of this epicentre
  3. 6.7 Prince William Sound, Alaska · 28 km NE of this epicentre
  4. 6.4 Prince William Sound, Alaska · 7 km ESE of this epicentre
  5. 6.3 60 km SW of Cordova, Alaska · 48 km SE 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 60.4793, -147.3638. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Chugach Census Area, AK 64 km (40 mi) E earthquakes near Chugach Census Area
Anchorage Municipality, AK 130 km (81 mi) NW earthquakes near Anchorage Municipality

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 1.5 44 km NNE of Chenega, Alaska
  2. 1.6 48 km W of Tatitlek, Alaska
  3. 1.7 41 km NE of Chenega, Alaska
  4. 2.3 55 km ESE of Whittier, Alaska
  5. 2.4 47 km WSW of Tatitlek, Alaska
  6. 1.5 55 km E of Whittier, Alaska
  7. 1.6 57 km SW of Tatitlek, Alaska
  8. 1.9 54 km NE of Chenega, Alaska
  9. 1.5 53 km NE of Chenega, Alaska
  10. 1.7 40 km NNE of Chenega, Alaska
  11. 2.3 46 km WSW of Tatitlek, Alaska
  12. 1.9 41 km NE of Chenega, Alaska
  13. 1.5 Southern Alaska
  14. 1.5 57 km NE of Chenega, Alaska
  15. 2.5 56 km NE of Chenega, 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.