Earthquake · reviewed by a seismologist
M 5.1ml
Earthquake near Big Lake, AK
No earthquake was likely felt in Big Lake in the 24 hours to 4:45 pm AKST (01:45 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 5.1 earthquake was recorded 2 km (1 mi) east of Big Lake, AK, at 3:23 am AKST on 7 November 2020 (12:23 UTC), 42 km deep. 1 person has reported feeling it to USGS.
USGS: 2 km E of Big Lake, Alaska
34 km (21 mi) N of Anchorage, AK
- When
- 3:23 am AKST on 7 November 2020 ()
- Where
- 2 km (1 mi) east of Big Lake, AK · earthquakes near Big Lake
- Magnitude
- M 5.1 (ml)
- Depth
- 42 km below the surface
- Felt
- 1 report · strongest reported intensity IV
- Measured shaking
- intensity IV (ShakeMap)
- USGS impact alert
- green
- Tsunami
- USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
- Nearest
- Anchorage Municipality, 51 km SE
- Nearest mapped fault
- Castle Mountain fault, 9 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 325 days ago
Earthquake alerts for Big Lake, AK
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Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.
At this magnitude and depth, people at rest would likely notice it out to about 201 km (125 mi) from the epicentre. In Big Lake, 2 km away, the estimate is intensity IV (light). 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: Big Lake 2 km, intensity IV · Knik-Fairview 17 km, intensity IV · Willow 26 km, intensity IV · Tanaina 28 km, intensity III · Eagle River 29 km, intensity III · Anchorage 34 km, intensity III · Palmer 43 km, intensity III · Fishhook 44 km, intensity III. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 670 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.1 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 250× the energy of this one
- Mineral, Virginia 2011 M 5.8 11× the energy of this one
- Magna, Utah 2020 M 5.7 7.9× the energy of this one
- This earthquake M 5.1 about 670 tons of TNT
- Around the size people start to feel M 3.0 this one released 1,400× 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 7.1 on 2018-11-30 — about 1,000 times the energy of this one.
Before 2016, the USGS record lists 19 earthquakes of M5 or more within 50 km; the five largest:
- 5.9 23 km NE of Willow, Alaska · 44 km NNE of this epicentre
- 5.6 11 km NW of Big Lake, Alaska · 13 km WNW of this epicentre
- 5.6 5 km N of Susitna, Alaska · 33 km WNW of this epicentre
- 5.5 2 km ENE of Eagle River, Alaska · 30 km SE of this epicentre
- 5.5 9 km E of Susitna, Alaska · 23 km W 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 61.5200, -149.9144. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Anchorage Municipality, AK | 51 km (32 mi) | SE | earthquakes near Anchorage Municipality |
| Matanuska-Susitna Borough, AK | 86 km (53 mi) | NNE | earthquakes near Matanuska-Susitna Borough |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
59 earthquakes have been recorded within 50 km since this one.
- 2.4 5 km SSW of Big Lake, Alaska
- 1.5 4 km NNW of Point MacKenzie, Alaska
- 1.6 2 km ENE of Big Lake, Alaska
- 1.7 3 km SE of Big Lake, Alaska
- 1.5 7 km WSW of Houston, Alaska
- 1.7 Southern Alaska
- 2.0 1 km NW of Big Lake, Alaska
- 1.6 2 km ENE of Big Lake, Alaska
- 1.8 3 km NE of Big Lake, Alaska
- 1.5 4 km NNE of Big Lake, Alaska
- 2.2 3 km ESE of Point MacKenzie, Alaska
- 2.1 0 km SSE of Big Lake, Alaska
- 2.4 1 km SE of Big Lake, Alaska
- 1.5 6 km SW of Houston, Alaska
- 1.9 4 km N 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
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.