QuakeIndex

Earthquake · reviewed by a seismologist

M 5.7ml

Earthquake near Rio Dell, CA

No earthquake was likely felt in Rio Dell in the 24 hours to 2:24 am PST (10:24 UTC). The last one was M 5.0, 126 km (78 mi) W, at 8:56 pm PST on 4 November 2026, estimated intensity II (weak) in town; 145 felt reports to USGS. Every earthquake near Rio Dell

This page: a magnitude 5.7 earthquake was recorded 49 km (31 mi) west-southwest of Rio Dell, CA, at 12:10 pm PST on 20 December 2021 (20:10 UTC), 17 km deep.

USGS: 29km W of Petrolia, CA

12:10 pm PST, Dec 20, 2021 · · 17 km deep · released about 4.5 kilotons of TNT

Every earthquake near Rio Dell Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Humboldt County 75 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
12:10 pm PST on 20 December 2021 ()
Where
49 km (31 mi) west-southwest of Rio Dell, CA · earthquakes near Rio Dell
Magnitude
M 5.7 (ml)
Depth
17 km below the surface
Felt
no reports yet
Measured shaking
intensity V (ShakeMap)
USGS impact alert
green
Nearest
Humboldt County, 75 km NE
Nearest mapped fault
Mattole Canyon fault, 16 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

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 285 km (177 mi) from the epicentre. In Rio Dell, 49 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: Ferndale 44 km, intensity IV · Rio Dell 49 km, intensity IV. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 4.5 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.7 would have released about 32 times as much.

  1. Loma Prieta, California 1989 M 6.9 75× the energy of this one
  2. Northridge, California 1994 M 6.7 38× the energy of this one
  3. Mineral, Virginia 2011 M 5.8 1.7× the energy of this one
  4. This earthquake M 5.7 about 4.5 kilotons of TNT
  5. Around the size people start to feel M 3.0 this one released 9,400× 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 5.8 on 2020-03-09 — about 1.5 times the energy of this one.

Before 2016, the USGS record lists 42 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.2 The 1992 Petrolia, California Earthquake · 34 km E of this epicentre
  2. 6.6 32 km SW of Ferndale, California · 11 km NNE of this epicentre
  3. 6.5 30 km WSW of Ferndale, California · 16 km NNE of this epicentre
  4. 6.5 The 2010 Eureka, California Earthquake · 40 km N of this epicentre
  5. 6.0 Near Rio Dell, California · 43 km ENE 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 40.2978, -124.6260. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Humboldt County, CA 75 km (46 mi) NE earthquakes near Humboldt County
Mendocino County, CA 139 km (87 mi) SE earthquakes near Mendocino 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. 3.9 6km NE of Petrolia, CA
  2. 3.3 18km SW of Ferndale, CA
  3. 2.2 12km SSW of Ferndale, CA
  4. 2.3 12km SW of Rio Dell, CA
  5. 2.4 11km SSW of Ferndale, CA
  6. 2.4 11km NNE of Petrolia, CA
  7. 2.4 14km NNW of Petrolia, CA
  8. 3.2 11km NNE of Petrolia, CA
  9. 2.0 4km ENE of Petrolia, CA
  10. 2.6 12km SSW of Ferndale, CA
  11. 2.7 15km SW of Ferndale, CA
  12. 2.6 14km N of Petrolia, CA
  13. 3.3 13km SSW of Ferndale, CA
  14. 2.4 12km S of Ferndale, CA
  15. 2.3 8km SSW of Ferndale, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.