Earthquake · reviewed by a seismologist
M 2.8md
Earthquake near Fortuna, CA
No earthquake was likely felt in Fortuna in the 24 hours to 10:18 pm PST (06:18 UTC). The last one was M 5.0, 123 km (76 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 Fortuna
This page: a magnitude 2.8 earthquake was recorded 48 km (30 mi) west-southwest of Fortuna, CA, at 2:38 pm PDT on 4 May 2021 (21:38 UTC), 23 km deep.
USGS: 35km WNW of Petrolia, CA
- When
- 2:38 pm PDT on 4 May 2021 ()
- Where
- 48 km (30 mi) west-southwest of Fortuna, CA · earthquakes near Fortuna
- Magnitude
- M 2.8 (md)
- Depth
- 23 km below the surface
- Felt
- no reports yet
- Nearest
- Humboldt County, 71 km ENE
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 1950 days ago
Earthquake alerts for Fortuna, CA
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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 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 12 km (7 mi) from the epicentre. In Fortuna, 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 420 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 36,000× the energy of this one
- Magna, Utah 2020 M 5.7 26,000× the energy of this one
- Around the size people start to feel M 3.0 2.3× the energy of this one
- This earthquake M 2.8 about 420 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 33,000 times the energy of this one.
Before 2016, the USGS record lists 43 earthquakes of M5 or more within 50 km; the five largest:
- 7.2 The 1992 Petrolia, California Earthquake · 39 km ESE of this epicentre
- 6.6 32 km SW of Ferndale, California · 11 km ESE of this epicentre
- 6.5 The 1932 Eureka, California Earthquake · 48 km NE of this epicentre
- 6.5 30 km WSW of Ferndale, California · 10 km E of this epicentre
- 6.5 The 2010 Eureka, California Earthquake · 26 km N 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 40.4223, -124.6793. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Humboldt County, CA | 71 km (44 mi) | ENE | earthquakes near Humboldt County |
| Mendocino County, CA | 152 km (95 mi) | SE | earthquakes near Mendocino County |
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.
- 2.8 9km W of Petrolia, CA
- 1.7 5km W of Petrolia, CA
- 2.7 8km W of Petrolia, CA
- 2.1 8km W of Petrolia, CA
- 2.9 12km WSW of Petrolia, CA
- 2.7 7km W of Petrolia, CA
- 2.7 33km WNW of Petrolia, CA
- 2.8 40km WNW of Petrolia, CA
- 1.7 16km SW of Ferndale, CA
- 2.8 56km WNW of Petrolia, CA
- 4.3 12km WSW of Petrolia, CA
- 2.1 4km SW of Petrolia, CA
- 2.4 9km W of Petrolia, CA
- 5.1 12km W of Petrolia, CA
- 2.4 21km 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
- 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.