QuakeIndex

Earthquake · reviewed by a seismologist

M 3.0ml

Earthquake near Rio Dell, CA

No earthquake was likely felt in Rio Dell in the 24 hours to 7:41 am PST (15:41 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 3.0 earthquake was recorded 8 km (5 mi) south-southwest of Rio Dell, CA, at 1:06 pm PST on 20 December 2021 (21:06 UTC), 27 km deep. 1 person has reported feeling it to USGS.

USGS: 8km SSW of Rio Dell, CA

1:06 pm PST, Dec 20, 2021 · · 27 km deep · released about 1,000 lb of TNT

Every earthquake near Rio Dell Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Humboldt County 35 kmTrinity County 89 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
1:06 pm PST on 20 December 2021 ()
Where
8 km (5 mi) south-southwest of Rio Dell, CA · earthquakes near Rio Dell
Magnitude
M 3.0 (ml)
Depth
27 km below the surface
Felt
1 report · strongest reported intensity IV
Nearest
Humboldt County, 35 km NNE
Nearest mapped fault
Little Salmon fault, 15 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 1717 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, people at rest would likely notice it out to about 26 km (16 mi) from the epicentre. In Rio Dell, 8 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: Rio Dell 8 km, intensity II · Fortuna 19 km, intensity II · Ferndale 19 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1,000 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 330,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 15,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 10,000× the energy of this one
  4. This earthquake M 3.0 about 1,000 lb of TNT

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 6.2 on 2021-12-20 — about 59,000 times the energy of this one.

Before 2016, the USGS record lists 33 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.2 The 1992 Petrolia, California Earthquake · 13 km SW of this epicentre
  2. 6.6 32 km SW of Ferndale, California · 36 km W of this epicentre
  3. 6.5 The 1932 Eureka, California Earthquake · 35 km NNW of this epicentre
  4. 6.5 30 km WSW of Ferndale, California · 36 km W of this epicentre
  5. 6.0 Near Rio Dell, California · 9 km NW 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 40.4317, -124.1348. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Humboldt County, CA 35 km (22 mi) NNE earthquakes near Humboldt County
Trinity County, CA 89 km (56 mi) ENE earthquakes near Trinity County
Mendocino County, CA 126 km (78 mi) SSE 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. 3.8 10km NNE of Petrolia, CA
  2. 2.7 13km WSW of Rio Dell, CA
  3. 2.6 9km N of Petrolia, CA
  4. 2.5 7km N of Petrolia, CA
  5. 2.8 9km NNE of Petrolia, CA
  6. 1.6 9km NNE of Petrolia, CA
  7. 2.8 15km WSW of Petrolia, CA
  8. 2.4 6km N of Petrolia, CA
  9. 1.8 20km SSE of Rio Dell, CA
  10. 2.3 8km NNE of Petrolia, CA
  11. 1.9 8km N of Petrolia, CA
  12. 2.2 8km NNE of Petrolia, CA
  13. 2.6 6km SE of Ferndale, CA
  14. 2.6 27km W of Petrolia, CA
  15. 2.8 8km NNE of Petrolia, 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.