Earthquake · reviewed by a seismologist
M 3.8mb
Earthquake near Casper, WY
No earthquake was likely felt in Casper in the 24 hours to 9:09 am MST (16:09 UTC). The last one was M 3.6, 260 km (162 mi) ENE, at 8:14 pm MST on 8 March 2025, estimated intensity II (weak) in town; 7 felt reports to USGS. Every earthquake near Casper
This page: a magnitude 3.8 earthquake was recorded 34 km (21 mi) east-northeast of Casper, WY, at 9:50 pm MDT on 1 August 2021 (03:50 UTC), 9.7 km deep. 266 people have reported feeling it to USGS.
USGS: 12 km NW of Rolling Hills, Wyoming
36 km (22 mi) ENE of Casper, WY
- When
- 9:50 pm MDT on 1 August 2021 ()
- Where
- 34 km (21 mi) east-northeast of Casper, WY · earthquakes near Casper
- Magnitude
- M 3.8 (mb)
- Depth
- 9.7 km below the surface
- Felt
- 266 reports · strongest reported intensity III
- Measured shaking
- intensity IV (ShakeMap)
- Nearest
- Converse County, 33 km E
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 1820 days ago
Earthquake alerts for Casper, WY
Get a notification in this browser when USGS records an earthquake near Casper, WY. No account or email needed.
Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.
At this magnitude and depth, people at rest would likely notice it out to about 82 km (51 mi) from the epicentre. In Casper, 34 km away, the estimate is intensity III (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.
Likely felt in: Casper 34 km, intensity III. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 7.6 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.8 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 22,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 1,000× the energy of this one
- Magna, Utah 2020 M 5.7 710× the energy of this one
- This earthquake M 3.8 about 7.6 tons of TNT
- Around the size people start to feel M 3.0 this one released 16× more
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
No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.
Before 2016, the USGS record since 1900 lists no earthquake of M5 or more within 50 km.
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 42.9946, -105.9330. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Converse County, WY | 33 km (21 mi) | E | earthquakes near Converse County |
| Natrona County, WY | 68 km (42 mi) | W | earthquakes near Natrona County |
| Niobrara County, WY | 119 km (74 mi) | E | earthquakes near Niobrara County |
| Platte County, WY | 125 km (78 mi) | SE | earthquakes near Platte County |
| Johnson County, WY | 128 km (80 mi) | NNW | earthquakes near Johnson County |
| Weston County, WY | 145 km (90 mi) | NE | earthquakes near Weston County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
1 earthquake has been recorded within 50 km since this one.
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
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.