QuakeIndex

Earthquake · reviewed by a seismologist

M 5.6mw

108km W of Petrolia, CA

Yes. A magnitude 5.6 earthquake was recorded 108km W of Petrolia, CA, at 11:44 am PDT on 21 May 2023 (18:44 UTC), 10 km deep. 623 people have reported feeling it to USGS.

· 10 km deep · released about 3.5 kilotons of TNT

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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 5.6 (mw)
Depth
10 km below the surface
Felt
623 reports · strongest reported intensity VI
Measured shaking
intensity IV (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 555 days ago

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.

At this magnitude and depth, people at rest would likely notice it out to about 273 km (170 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 3.5 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.6 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 48× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 2.1× the energy of this one
  3. Magna, Utah 2020 M 5.7 1.5× the energy of this one
  4. This earthquake M 5.6 about 3.5 kilotons of TNT
  5. Around the size people start to feel M 3.0 this one released 7,400× 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 5.8 on 2020-03-09 — about 1.9 times the energy of this one.

Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:

  1. 5.0 65 km WSW of Ferndale, California · 48 km E 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 40.3775, -125.5628. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.6 150 km W of Ferndale, California
  2. 2.4 81 km WNW of Ferndale, CA
  3. 2.7 138 km WNW of Petrolia, CA
  4. 2.8 96 km WNW of Petrolia, CA
  5. 3.0 101 km W of Petrolia, CA
  6. 2.7 73 km WNW of Petrolia, CA
  7. 3.0 75 km WNW of Petrolia, CA
  8. 2.9 157 km W of Ferndale, California
  9. 2.8 80 km WNW of Petrolia, CA
  10. 2.7 82 km WNW of Petrolia, CA
  11. 2.6 128 km W of Petrolia, CA
  12. 3.5 113 km W of Petrolia, CA
  13. 2.8 76 km W of Petrolia, CA
  14. 2.9 79 km W of Ferndale, CA
  15. 3.0 69 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.