Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Fortuna, CA
No earthquake was likely felt in Fortuna in the 24 hours to 2:54 am PST (10:54 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 1.8 earthquake was recorded 42 km (26 mi) southwest of Fortuna, CA, at 5:20 am PDT on 16 August 2021 (12:20 UTC), 11 km deep.
USGS: 16km W of Petrolia, CA
- When
- 5:20 am PDT on 16 August 2021 ()
- Where
- 42 km (26 mi) southwest of Fortuna, CA · earthquakes near Fortuna
- Magnitude
- M 1.8 (md)
- Depth
- 11 km below the surface
- Felt
- no reports yet
- Nearest
- Humboldt County, 64 km NE
- Nearest mapped fault
- Mattole Canyon fault, 5 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 1907 days ago
Earthquake alerts for Fortuna, CA
Get a notification in this browser when USGS records an earthquake near Fortuna, CA. No account or email needed.
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 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 8 km (5 mi) from the epicentre. In Fortuna, 42 km away, the estimate is intensity I (not felt). 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 17 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 900,000× the energy of this one
- Magna, Utah 2020 M 5.7 640,000× the energy of this one
- Around the size people start to feel M 3.0 57× the energy of this one
- This earthquake M 1.8 about 17 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 5.6 on 2019-06-23 — about 420,000 times the energy of this one.
Before 2016, the USGS record lists 39 earthquakes of M5 or more within 50 km; the five largest:
- 7.2 The 1992 Petrolia, California Earthquake · 21 km E of this epicentre
- 6.6 32 km SW of Ferndale, California · 11 km NW of this epicentre
- 6.5 The 1932 Eureka, California Earthquake · 50 km NNE of this epicentre
- 6.5 30 km WSW of Ferndale, California · 16 km NNW of this epicentre
- 6.5 The 2010 Eureka, California Earthquake · 43 km NNW 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 40.3043, -124.4693. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Humboldt County, CA | 64 km (40 mi) | NE | earthquakes near Humboldt County |
| Trinity County, CA | 121 km (75 mi) | ENE | earthquakes near Trinity County |
| Mendocino County, CA | 131 km (81 mi) | SE | earthquakes near Mendocino County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
54 earthquakes have been recorded within 50 km since this one.
- 2.3 4km NNE of Petrolia, CA
- 4.4 5km NNE of Petrolia, CA
- 2.5 19km W of Petrolia, CA
- 2.4 26km WNW of Petrolia, CA
- 2.9 23km W of Petrolia, CA
- 2.2 12km WSW of Petrolia, CA
- 1.7 19km WNW of Petrolia, CA
- 1.7 4km NNW of Ferndale, CA
- 3.8 18km WSW of Petrolia, CA
- 2.8 56km W of Ferndale, CA
- 1.6 12km SE of Petrolia, CA
- 2.8 56km W of Ferndale, CA
- 2.4 14km SW of Ferndale, CA
- 2.5 9km SW of Petrolia, CA
- 2.8 7km WSW 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.