QuakeIndex

Earthquake · reviewed by a seismologist

M 5.5mw

Lake Almanor Earthquake

Yes. A magnitude 5.5 earthquake was recorded in Lake Almanor Earthquake, at 4:19 pm PDT on 11 May 2023 (23:19 UTC), 5.8 km deep. 7,030 people have reported feeling it to USGS.

· 5.8 km deep · released about 2.5 kilotons of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Plumas County 34 kmLassen County 70 kmButte County 73 kmSierra County 86 kmTehama County 96 kmShasta County 100 kmNevada County 105 kmYuba County 106 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 5.5 (mw)
Depth
5.8 km below the surface
Felt
7,030 reports · strongest reported intensity VI
Measured shaking
intensity VI (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Nearest
Plumas County, 34 km SE
Nearest mapped fault
Almanor fault, 3 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 565 days ago

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 258 km (160 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.

Likely felt in: Westwood 14 km, intensity V · Greenville 15 km, intensity V · Chester 15 km, intensity V · East Quincy 35 km, intensity IV · Susanville 45 km, intensity IV. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 2.5 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 68× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 3× the energy of this one
  3. Magna, Utah 2020 M 5.7 2.1× the energy of this one
  4. This earthquake M 5.5 about 2.5 kilotons of TNT
  5. Around the size people start to feel M 3.0 this one released 5,200× 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.

Where

Epicentre 40.2042, -121.1095. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Plumas County, CA 34 km (21 mi) SE earthquakes near Plumas County
Lassen County, CA 70 km (44 mi) NE earthquakes near Lassen County
Butte County, CA 73 km (45 mi) SW earthquakes near Butte County
Sierra County, CA 86 km (53 mi) SE earthquakes near Sierra County
Tehama County, CA 96 km (60 mi) W earthquakes near Tehama County
Shasta County, CA 100 km (62 mi) NW earthquakes near Shasta County

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

Aftershocks so far

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

  1. 2.3 4km NNW of Canyondam, CA
  2. 2.2 4km NW of Canyondam, CA
  3. 2.3 1km NE of Almanor, CA
  4. 2.2 4km WNW of Canyondam, CA
  5. 2.3 4km NNW of Canyondam, CA
  6. 2.2 4km N of Almanor, CA
  7. 2.2 2km ESE of Prattville, CA
  8. 2.4 2km NE of Prattville, CA
  9. 2.9 4km SE of Prattville, CA
  10. 2.3 4km ESE of Prattville, CA
  11. 2.3 2km N of Prattville, CA
  12. 2.9 4km NW of Canyondam, CA
  13. 2.3 2km ESE of Prattville, CA
  14. 2.0 3km NNE of Almanor, CA
  15. 2.9 1km N of Prattville, CA

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

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