California earthquakes

M3.3 earthquake 27km W of Petrolia, CA

A magnitude 3.3 earthquake struck 27km W of Petrolia, CA on Mon, Dec 20, 2021, 12:47 PM PST (20:47 UTC), 18 km (11 mi) below the surface.

A larger quake followed: M4.6 50km W of Petrolia, CA. This one was a foreshock.

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Map

Where this earthquake was located, with the others nearby. Select one for its page.

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The earthquake

Magnitude: 3.3 (ML, local (Richter)), minor
Magnitude from: Northern California Seismic System
Local time: Mon, Dec 20, 2021, 12:47 PM PST
UTC: 2021-12-20 20:47:43 UTC
Depth: 17.9 km (11.1 mi), shallow
Epicenter: 40.320° N, 124.600° W
Region: California
Felt reports: 13
Strongest shaking: II, weak shaking
Tsunami flag: No
Status: Reviewed by a seismologist

Magnitude estimates

Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.

Mag.	Scale	Computed by	Notes
3.28	ML, local (Richter)	Northern California Seismic System	Preferred · Final · ±0.226 · 42 stations
3.2	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.05 · 52 stations
4.1	Mw, moment	EW	Preliminary · ±0.2 · 10 stations

Shaking

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

Strongest estimated: II, weak shaking
Peak ground acceleration: 0.2% of gravity
Peak ground velocity: -2.6 cm/s
Map: Automatic

USGS ShakeMap: estimated shaking intensity around the epicenter — Estimated shaking intensity. Map: USGS ShakeMap.

Did you feel it?

13 people reported to the USGS what they felt; the strongest reported shaking was V, moderate shaking.

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 0.5 km horizontally, 0.4 km in depth
Magnitude uncertainty: ±0.23
Depth from: From location
Station coverage gap: 253°, poorly surrounded by stations
Stations used: 35

Nearest places

Distance and direction from each place to the epicenter, with its forecast.

Nearby

Within 100 km, magnitude 1.5 and up: at least 200 in the 60 days after this one and 57 in the 30 days before it.

After

The first 60 of at least 200.

Before

Earthquakes today California earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event nc73666361 (also filed as ew1640033270, us6000gdyg). Read Sun, Oct 4, 2026, 8:31 AM UTC.