QuakeIndex

Earthquake · reviewed by a seismologist

M 4.3ml

Earthquake near Willow, AK

No earthquake was likely felt in Willow in the 24 hours to 11:58 pm AKST (08:58 UTC). The last one was M 2.8, 20 km (12 mi) S, at 6:17 am AKST on 6 November 2026, estimated intensity II (weak) in town; 3 felt reports to USGS. Every earthquake near Willow

This page: a magnitude 4.3 earthquake was recorded 30 km (19 mi) west-northwest of Willow, AK, at 10:13 pm AKDT on 11 August 2021 (06:13 UTC), 60 km deep. 401 people have reported feeling it to USGS.

USGS: 30 km WNW of Willow, Alaska

80 km (50 mi) NNW of Anchorage, AK

10:13 pm AKDT, Aug 11, 2021 · · 60 km deep · released about 43 tons of TNT

Every earthquake near Willow Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Matanuska-Susitna Borough 70 kmAnchorage Municipality 103 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
10:13 pm AKDT on 11 August 2021 ()
Where
30 km (19 mi) west-northwest of Willow, AK · earthquakes near Willow
Magnitude
M 4.3 (ml)
Depth
60 km below the surface
Felt
401 reports · strongest reported intensity III
Measured shaking
intensity III (ShakeMap)
Nearest
Matanuska-Susitna Borough, 70 km NE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1847 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 105 km (65 mi) from the epicentre. In Willow, 30 km away, the estimate is intensity II (weak). 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.

Likely felt in: Willow 30 km, intensity II · Susitna North 49 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 43 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.3 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 4,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 180× the energy of this one
  3. Magna, Utah 2020 M 5.7 130× the energy of this one
  4. This earthquake M 4.3 about 43 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 89× 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 5.2 on 2019-09-17 — about 22 times the energy of this one.

Before 2016, the USGS record lists 19 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 27 km SE of Skwentna, Alaska · 26 km WSW of this epicentre
  2. 5.9 23 km NE of Willow, Alaska · 43 km E of this epicentre
  3. 5.7 19 km E of Skwentna, Alaska · 28 km WNW of this epicentre
  4. 5.6 11 km NW of Big Lake, Alaska · 39 km SE of this epicentre
  5. 5.6 5 km N of Susitna, Alaska · 30 km S 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 61.8704, -150.5529. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Matanuska-Susitna Borough, AK 70 km (44 mi) NE earthquakes near Matanuska-Susitna Borough
Anchorage Municipality, AK 103 km (64 mi) SE 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 29 km NNW of Susitna, Alaska
  2. 1.8 24 km SW of Trapper Creek, Alaska
  3. 2.3 23 km WNW of Susitna, Alaska
  4. 1.6 22 km NW of Willow, Alaska
  5. 1.5 11 km W of Susitna North, Alaska
  6. 2.0 13 km ESE of Susitna, Alaska
  7. 1.9 24 km ESE of Skwentna, Alaska
  8. 3.0 26 km WSW of Trapper Creek, Alaska
  9. 1.9 27 km NW of Susitna, Alaska
  10. 1.8 24 km WNW of Susitna, Alaska
  11. 1.8 12 km WSW of Big Lake, Alaska
  12. 1.6 26 km NW of Willow, Alaska
  13. 1.9 31 km WNW of Susitna, Alaska
  14. 1.7 29 km NNW of Susitna, Alaska
  15. 1.8 9 km NNW of Big Lake, 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.