M3.1 earthquake 6km W of Petrolia, CA

A magnitude 3.1 earthquake struck 6km W of Petrolia, CA on Fri, Aug 20, 2021, 11:01 AM PDT (18:01 UTC), 28 km (17 mi) below the surface.

A larger quake followed: M4.5 10km SW of Petrolia, CA. This one was a foreshock.

Map

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

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
3.08	ML, local (Richter)	Northern California Seismic System	Preferred · Final · ±0.181 · 15 stations
2.9	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.035 · 108 stations

1 person reported to the USGS what they felt; the strongest reported shaking was II, weak shaking.

Reviewed by a seismologist.

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

Within 100 km, magnitude 1.5 and up: 67 in the 60 days after this one and 43 in the 30 days before it.

The first 60 of 67.

From the USGS Earthquake Hazards Program and its partner networks, event nc73612571 (also filed as us6000f90u). Read Sun, Oct 4, 2026, 7:54 AM UTC.