QuakeIndex

Earthquake · reviewed by a seismologist

M 3.3ml

Earthquake near Big Lake, AK

No earthquake was likely felt in Big Lake in the 24 hours to 5:06 am AKST (14:06 UTC). The last one was M 2.8, 6 km (4 mi) NW, at 6:17 am AKST on 6 November 2026, estimated intensity II (weak) in town; 3 felt reports to USGS. Every earthquake near Big Lake

This page: a magnitude 3.3 earthquake was recorded 47 km (29 mi) west-southwest of Big Lake, AK, at 2:21 pm AKDT on 8 October 2018 (22:21 UTC), 58 km deep. 9 people have reported feeling it to USGS.

USGS: 20 km SW of Susitna, Alaska

54 km (33 mi) WNW of Anchorage, AK

2:21 pm AKDT, Oct 8, 2018 · · 58 km deep · released about 1.3 tons of TNT

Every earthquake near Big Lake Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Anchorage Municipality 86 kmMatanuska-Susitna Borough 116 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
2:21 pm AKDT on 8 October 2018 ()
Where
47 km (29 mi) west-southwest of Big Lake, AK · earthquakes near Big Lake
Magnitude
M 3.3 (ml)
Depth
58 km below the surface
Felt
9 reports · strongest reported intensity II
Measured shaking
intensity II (ShakeMap)
Nearest
Anchorage Municipality, 86 km ESE
Nearest mapped fault
Castle Mountain fault, 4 km from its surface trace — near is not the same as on
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 it was probably too small to be felt, even directly above it. In Big Lake, 47 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.

How big was it?

This earthquake released about 1.3 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.3 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 130,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 5,600× the energy of this one
  3. Magna, Utah 2020 M 5.7 4,000× the energy of this one
  4. This earthquake M 3.3 about 1.3 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 2.8× 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 4.3 on 2016-02-28 — about 32 times the energy of this one.

Before 2016, the USGS record lists 26 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 27 km SE of Skwentna, Alaska · 44 km NNW of this epicentre
  2. 6.8 Southern Alaska · 40 km SSW of this epicentre
  3. 6.8 4 km NE of Beluga, Alaska · 30 km SSW of this epicentre
  4. 5.8 17 km NW of Beluga, Alaska · 36 km SW of this epicentre
  5. 5.8 27 km N of Beluga, Alaska · 13 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 61.4241, -150.8075. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Anchorage Municipality, AK 86 km (53 mi) ESE earthquakes near Anchorage Municipality
Matanuska-Susitna Borough, AK 116 km (72 mi) NE earthquakes near Matanuska-Susitna Borough
Kenai Peninsula Borough, AK 143 km (89 mi) SW earthquakes near Kenai Peninsula Borough

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

Aftershocks so far

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

  1. 2.3 11 km SE of Tyonek, Alaska
  2. 1.7 13 km WNW of Beluga, Alaska
  3. 2.8 18 km S of Susitna, Alaska
  4. 2.4 42 km W of Susitna, Alaska
  5. 1.9 34 km SSE of Skwentna, Alaska
  6. 2.0 26 km WSW of Anchorage, Alaska
  7. 1.9 31 km SSE of Skwentna, Alaska
  8. 1.6 26 km NE of Point Possession, Alaska
  9. 2.1 24 km WSW of Anchorage, Alaska
  10. 1.9 17 km W of Susitna, Alaska
  11. 1.5 20 km SSW of Susitna, Alaska
  12. 1.7 26 km S of Susitna, Alaska
  13. 1.7 26 km ENE of Beluga, Alaska
  14. 2.1 16 km W of Point MacKenzie, Alaska
  15. 1.7 Southern 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.