California earthquakes

M3.9 earthquake 17 km NNE of Mesa, California

A magnitude 3.9 earthquake struck 17 km NNE of Mesa, California on Thu, Jul 31, 1986, 11:34 PM PDT (06:34 UTC), 10 km (6 mi) below the surface.

A larger quake followed: M4.0 22 km ENE of Sunny Slopes, California. This one was a foreshock.

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Map

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

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The earthquake

Magnitude: 3.9 (ml), minor
Local time: Thu, Jul 31, 1986, 11:34 PM PDT
UTC: 1986-08-01 06:34:42 UTC
Depth: 10.2 km (6.3 mi), shallow
Epicenter: 37.559° N, 118.449° W
Region: California
Tsunami flag: No
Status: Reviewed by a seismologist

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 0.2 km horizontally, 0.5 km in depth
Depth from: From location
Station coverage gap: 52°
Stations used: 46

Nearest places

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

Nearby

Within 100 km, magnitude 1.5 and up: 200 in the 60 days after this one and 0 in the 30 days before it.

After

The first 60 of 200.

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Sources

From the USGS Earthquake Hazards Program and its partner networks, event nc86978 (also filed as ci129433, usp0002wsc). Read Tue, Sep 22, 2026, 7:43 AM UTC.