QuakeIndex

Earthquake · reviewed by a seismologist

M 4.7mw

85 km W of Petrolia, CA

Yes. A magnitude 4.7 earthquake was recorded 85 km W of Petrolia, CA, at 7:41 pm PDT on 28 August 2026 (02:41 UTC), 10 km deep. 102 people have reported feeling it to USGS.

· 10 km deep · released about 190 tons of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Humboldt County 117 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
Magnitude
M 4.7 (mw)
Depth
10 km below the surface
Felt
102 reports · strongest reported intensity IV
Measured shaking
intensity III (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Nearest
Humboldt County, 117 km ENE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 48 days ago

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 163 km (101 mi) from the epicentre. 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 190 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.7 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 870× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 39× the energy of this one
  3. Magna, Utah 2020 M 5.7 28× the energy of this one
  4. This earthquake M 4.7 about 190 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 410× 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 7.0 on 2024-12-05 — about 2,500 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 5.9 61 km WSW of Ferndale, California · 27 km E of this epicentre
  2. 5.8 near the coast of Northern California · 45 km NNE of this epicentre
  3. 5.5 54 km WSW of Ferndale, California · 39 km ESE of this epicentre
  4. 5.5 60 km WSW of Ferndale, California · 31 km ESE of this epicentre
  5. 5.4 51 km W of Ferndale, 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 40.4500, -125.2723. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Humboldt County, CA 117 km (73 mi) ENE earthquakes near Humboldt County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 5.0 111 km W of Petrolia, CA
  2. 2.7 66 km W of Petrolia, CA
  3. 2.7 63 km W of Petrolia, CA
  4. 1.7 53 km WSW of Petrolia, CA
  5. 3.4 70 km W of Ferndale, CA
  6. 3.1 80 km WNW of Ferndale, CA
  7. 3.2 74 km W of Petrolia, CA
  8. 2.5 53 km WNW of Petrolia, CA
  9. 4.8 97 km W of Petrolia, CA
  10. 2.5 40 km W of Petrolia, CA
  11. 2.6 47 km WNW of Petrolia, CA
  12. 2.3 103 km W of Petrolia, CA
  13. 2.5 52 km W of Petrolia, CA
  14. 2.6 61 km W of Petrolia, CA
  15. 2.6 99 km 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.