M3.6 earthquake 99km W of Trinidad, CA

A magnitude 3.6 earthquake struck 99km W of Trinidad, CA on Wed, Mar 17, 2021, 7:21 AM PDT (14:21 UTC), 5 km (3 mi) below the surface.

A larger quake followed: M4.7 76km W of Petrolia, 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
3.6	Mw, moment	Northern California Seismic System	Preferred · Final · 3 stations
3.6	Mwr, regional moment	USGS National Earthquake Information Center	Reviewed · 3 stations

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

4 people reported to the USGS what they felt; the strongest reported shaking was III, weak shaking.

Reviewed by a seismologist.

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

Within 100 km, magnitude 1.5 and up: 15 in the 60 days after this one and 9 in the 30 days before it.

From the USGS Earthquake Hazards Program and its partner networks, event nc73538445 (also filed as us7000dka7). Read Sun, Oct 4, 2026, 2:58 PM UTC.