M3.2 earthquake 6 km SE of Sunol, California

A magnitude 3.2 earthquake struck 6 km SE of Sunol, California on Sun, Aug 27, 1978, 8:32 PM PDT (03:32 UTC), 10 km (6 mi) below the surface.

A larger quake followed: M4.2 37km SSW of Half Moon Bay, CA. 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
3.21	Md, duration	Northern California Seismic System	Preferred · Final · ±0.23 · 34 stations
2.9	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: 76 in the 60 days after this one and 34 in the 30 days before it.

The first 60 of 76.

From the USGS Earthquake Hazards Program and its partner networks, event nc1041914 (also filed as usp0000w8h). Read Thu, Oct 1, 2026, 5:15 PM UTC.