M3.1 earthquake 7 km WNW of Cobb, California

A magnitude 3.1 earthquake struck 7 km WNW of Cobb, California on Sat, Oct 31, 1987, 5:42 PM PST (01:42 UTC), -1 km (-1 mi) below the surface.

A larger quake followed: M3.2 5 km SW of Cobb, 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
3.1	ML, local (Richter)	Northern California Seismic System	Preferred · Final · 2 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: 166 in the 60 days after this one and 102 in the 30 days before it.

The first 60 of 166.

From the USGS Earthquake Hazards Program and its partner networks, event nc107873 (also filed as usp00039ta). Read Fri, Oct 2, 2026, 4:03 PM UTC.