M2.5 earthquake 10 km ESE of Challis, Idaho

A magnitude 2.5 earthquake struck 10 km ESE of Challis, Idaho on Wed, Oct 21, 2015, 11:57 PM MDT (05:57 UTC), 11 km (7 mi) below the surface.

A larger quake followed: M3.5 5 km NW of Challis, Idaho. 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
2.5	ML, local (Richter)	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.226 · 18 stations
2.54	ML, local (Richter)	Montana Bureau of Mines and Geology	Final · ±0.226 · 18 stations

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: 82 in the 60 days after this one and 14 in the 30 days before it.

The first 60 of 82.

From the USGS Earthquake Hazards Program and its partner networks, event us10003qlz (also filed as mb80103019). Read Sat, Oct 3, 2026, 3:07 AM UTC.