QuakeIndex

Earthquake · reviewed by a seismologist

M 2.5md

Earthquake near Rio Dell, CA

No earthquake was likely felt in Rio Dell in the 24 hours to 10:18 pm PST (06:18 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 2.5 earthquake was recorded 48 km (30 mi) west-southwest of Rio Dell, CA, at 10:59 pm PDT on 18 April 2021 (05:59 UTC), 20 km deep.

USGS: 28km W of Petrolia, CA

10:59 pm PDT, Apr 18, 2021 · · 20 km deep · released about 150 lb of TNT

Every earthquake near Rio Dell Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Humboldt County 73 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
10:59 pm PDT on 18 April 2021 ()
Where
48 km (30 mi) west-southwest of Rio Dell, CA · earthquakes near Rio Dell
Magnitude
M 2.5 (md)
Depth
20 km below the surface
Felt
no reports yet
Nearest
Humboldt County, 73 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 1958 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 10 km (6 mi) from the epicentre. In Rio Dell, 48 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 150 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 99,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 70,000× the energy of this one
  3. Around the size people start to feel M 3.0 6.2× the energy of this one
  4. This earthquake M 2.5 about 150 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 5.8 on 2020-03-09 — about 89,000 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 · 33 km E of this epicentre
  2. 6.6 32 km SW of Ferndale, California · 10 km NE of this epicentre
  3. 6.5 30 km WSW of Ferndale, California · 14 km NNE of this epicentre
  4. 6.5 The 2010 Eureka, California Earthquake · 38 km N of this epicentre
  5. 6.0 Near Rio Dell, California · 41 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 40.3120, -124.6197. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Humboldt County, CA 73 km (46 mi) NE earthquakes near Humboldt County
Mendocino County, CA 140 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

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

  1. 2.4 9km W of Petrolia, CA
  2. 5.1 12km W of Petrolia, CA
  3. 2.4 21km W of Petrolia, CA
  4. 2.4 8km WSW of Petrolia, CA
  5. 1.8 9km SSW of Ferndale, CA
  6. 1.6 9km SSW of Ferndale, CA
  7. 1.7 9km SSW of Ferndale, CA
  8. 3.4 57km W of Petrolia, CA
  9. 2.0 22km W of Petrolia, CA
  10. 2.8 21km W of Petrolia, CA
  11. 2.0 11km SSW of Ferndale, CA
  12. 1.7 22km W of Petrolia, CA
  13. 2.0 15km SW of Petrolia, CA
  14. 2.3 11km SSW of Ferndale, CA
  15. 2.9 66km W 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.