M2.8 earthquake 56km WNW of Petrolia, CA

A magnitude 2.8 earthquake struck 56km WNW of Petrolia, CA on Wed, Jul 21, 2021, 3:36 AM PDT (10:36 UTC), 15 km (10 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
2.79	Md, duration	Northern California Seismic System	Preferred · Final · ±0.138 · 40 stations
2.6	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.043 · 70 stations

3 people 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 22 in the 30 days before it.

The first 60 of 67.

From the USGS Earthquake Hazards Program and its partner networks, event nc73596741 (also filed as us6000exkz). Read Sun, Oct 4, 2026, 1:47 PM UTC.