M2.8 earthquake 48 km SSE of Mammoth, Wyoming

A magnitude 2.8 earthquake struck 48 km SSE of Mammoth, Wyoming on Mon, Dec 31, 2018, 3:21 AM MST (10:21 UTC), 3 km (2 mi) below the surface.

A larger quake followed: M3.1 23 km SSE of West Yellowstone, Montana. 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
2.75	ML, local (Richter)	University of Utah Seismograph Stations	Preferred · Final · ±0.229 · 4 stations
2.8	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.229 · 4 stations

1 person reported to the USGS what they felt; the strongest reported shaking was II, 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: 40 in the 60 days after this one and 34 in the 30 days before it.

From the USGS Earthquake Hazards Program and its partner networks, event uu60016814 (also filed as us2000izv3). Read Sat, Oct 3, 2026, 10:07 AM UTC.