M3.4 earthquake 6 km W of Cobb, California

A magnitude 3.4 earthquake struck 6 km W of Cobb, California on Fri, Sep 5, 1986, 11:13 AM PDT (18:13 UTC), -1 km (0 mi) below the surface.

A larger quake followed: M4.5 26 km NE of Potter Valley, California. 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
3.38	Md, duration	Northern California Seismic System	Preferred · Final · ±0.22 · 16 stations
3.1	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed

No one has reported feeling this quake to the USGS.

Reviewed by a seismologist.

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

Within 100 km, magnitude 1.5 and up: 141 in the 60 days after this one and 101 in the 30 days before it.

The first 60 of 141.

From the USGS Earthquake Hazards Program and its partner networks, event nc81446 (also filed as usp0002xv3). Read Fri, Oct 2, 2026, 1:42 AM UTC.