QuakeIndex

Earthquake · reviewed by a seismologist

M 2.3ml

Earthquake near Challis, ID

No earthquake was likely felt in Challis in the 24 hours to 8:34 pm MST (03:34 UTC). The last one was M 2.0, 9 km (6 mi) SSW, at 1:32 am MDT on 17 August 2026, estimated intensity II (weak) in town. Every earthquake near Challis

This page: a magnitude 2.3 earthquake was recorded 45 km (28 mi) west-southwest of Challis, ID, at 8:02 pm MDT on 20 September 2021 (02:02 UTC), 19 km deep. 1 person has reported feeling it to USGS.

USGS: 20 km ENE of Stanley, Idaho

8:02 pm MDT, Sep 20, 2021 · · 19 km deep · released about 85 lb of TNT

Every earthquake near Challis Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Custer County 38 kmBoise County 87 kmCamas County 90 kmValley County 93 kmLemhi County 96 kmElmore County 118 kmBlaine County 119 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
8:02 pm MDT on 20 September 2021 ()
Where
45 km (28 mi) west-southwest of Challis, ID · earthquakes near Challis
Idaho today
every earthquake in Idaho in the last 24 hours
Magnitude
M 2.3 (ml)
Depth
19 km below the surface
Felt
1 report · strongest reported intensity II
Nearest
Custer County, 38 km E
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1806 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 4 km (2 mi) from the epicentre. In Challis, 45 km away, the estimate is intensity II (weak). Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

How big was it?

This earthquake released about 85 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.3 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 180,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 130,000× the energy of this one
  3. Around the size people start to feel M 3.0 11× the energy of this one
  4. This earthquake M 2.3 about 85 lb of TNT

Energy from the Gutenberg–Richter relation (log10E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 6.5 on 2020-03-31 — about 2,000,000 times the energy of this one.

Before 2016, the USGS record lists 5 earthquakes of M5 or more within 50 km:

  1. 6.1 37 km N of Stanley, Idaho · 31 km NNW of this epicentre
  2. 6.0 44 km NNW of Stanley, Idaho · 44 km NW of this epicentre
  3. 5.5 22 km E of Clayton, Idaho · 48 km E of this epicentre
  4. 5.4 23 km E of Clayton, Idaho · 50 km E of this epicentre
  5. 5.1 9 km SE of Challis, Idaho · 47 km ENE of this epicentre

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 44.3085, -114.7224. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Custer County, ID 38 km (23 mi) E earthquakes near Custer County
Boise County, ID 87 km (54 mi) WSW earthquakes near Boise County
Camas County, ID 90 km (56 mi) S earthquakes near Camas County
Valley County, ID 93 km (58 mi) NW earthquakes near Valley County
Lemhi County, ID 96 km (59 mi) NE earthquakes near Lemhi County
Elmore County, ID 118 km (73 mi) SSW earthquakes near Elmore County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

60 earthquakes have been recorded within 50 km since this one.

  1. 1.6 19 km NE of Stanley, Idaho
  2. 2.4 31 km NW of Stanley, Idaho
  3. 2.2 25 km NW of Stanley, Idaho
  4. 2.4 31 km NW of Stanley, Idaho
  5. 2.4 10 km WNW of Stanley, Idaho
  6. 2.2 6 km NW of Stanley, Idaho
  7. 2.4 8 km NW of Stanley, Idaho
  8. 1.9 36 km NW of Stanley, Idaho
  9. 2.1 34 km NW of Stanley, Idaho
  10. 2.6 11 km NW of Stanley, Idaho
  11. 1.8 27 km NW of Stanley, Idaho
  12. 2.2 33 km NW of Stanley, Idaho
  13. 2.3 11 km NW of Stanley, Idaho
  14. 2.3 7 km NW of Stanley, Idaho
  15. 3.0 11 km NW of Stanley, Idaho

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.