California earthquakes

M2.8 earthquake 20 km SW of Three Rocks, California

A magnitude 2.8 earthquake struck 20 km SW of Three Rocks, California on Thu, Oct 17, 1991, 12:40 AM PDT (07:40 UTC), 19 km (12 mi) below the surface.

A larger quake followed: M3.5 8 km ENE of Coalinga, California. This one was a foreshock.

Coalinga forecast More in California

Map

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

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The earthquake

Magnitude: 2.8 (Md, duration), micro
Magnitude from: Northern California Seismic System
Local time: Thu, Oct 17, 1991, 12:40 AM PDT
UTC: 1991-10-17 07:40:03 UTC
Depth: 18.6 km (11.5 mi), shallow
Epicenter: 36.381° N, 120.561° W
Region: California
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
2.84	Md, duration	Northern California Seismic System	Preferred · Final · ±0.15 · 149 stations
2.8	Mc	Southern California Seismic Network	Final · 37 stations

Did you feel it?

No one has reported feeling this quake to the USGS.

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 0.3 km horizontally, 0.4 km in depth
Magnitude uncertainty: ±0.15
Depth from: From location
Station coverage gap: 103°
Stations used: 59

Nearest places

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

Nearby

Within 100 km, magnitude 1.5 and up: 152 in the 60 days after this one and 117 in the 30 days before it.

After

The first 60 of 152.

Before

Earthquakes today California earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event nc234523 (also filed as ci2031904). Read Mon, Oct 5, 2026, 2:36 PM UTC.