California earthquakes

M1.8 earthquake 1 km WNW of Concord, California

A magnitude 1.8 earthquake struck 1 km WNW of Concord, California on Thu, May 28, 1987, 3:34 AM PDT (10:34 UTC), 12 km (8 mi) below the surface.

A larger quake followed: M3.6 13 km N of Morgan Hill, 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
1.8 (md), micro
Local time
UTC
1987-05-28 10:34:59 UTC
Depth
12.3 km (7.7 mi), shallow
Epicenter
37.983° N, 122.041° W
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
Magnitude uncertainty
±0.14
Depth from
From location
Station coverage gap
44°
Stations used
32

Nearest places

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

Nearby

Within 100 km, magnitude 1.5 and up: 82 in the 60 days after this one and 63 in the 30 days before it.

After

The first 60 of 82.

Before

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Sources

From the USGS Earthquake Hazards Program and its partner networks, event nc101045. Read Mon, Sep 28, 2026, 6:22 AM UTC.