Earthquake · reviewed by a seismologist
M 1.5ml
25 km SE of Mammoth, Wyoming
Yes. A magnitude 1.5 earthquake was recorded 25 km SE of Mammoth, Wyoming, at 9:41 am MDT on 21 August 2021 (15:41 UTC), 7.0 km deep.
- When
- Magnitude
- M 1.5 (ml)
- Depth
- 7.0 km below the surface
- Felt
- no reports yet
- Nearest
- Park County, 71 km N
- Nearest mapped fault
- Mirror Plateau faults, 12 km from its surface trace — near is not the same as on
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 1906 days ago
Earthquake alerts for West Yellowstone, MT
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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 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 7 km (4 mi) from the epicentre. 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 5.4 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 2,800,000× the energy of this one
- Magna, Utah 2020 M 5.7 2,000,000× the energy of this one
- Around the size people start to feel M 3.0 180× the energy of this one
- This earthquake M 1.5 about 5.4 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
No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.
Before 2016, the USGS record lists 12 earthquakes of M5 or more within 50 km; the five largest:
- 6.5 14 km N of Madison Junction, Wyoming · 35 km W of this epicentre
- 6.3 22 km SW of Mammoth, Wyoming · 32 km W of this epicentre
- 6.0 21 km E of West Yellowstone, Montana · 36 km WSW of this epicentre
- 5.9 26 km SSE of Mammoth, Wyoming · 15 km SW of this epicentre
- 5.7 13 km SSW of Mammoth, Wyoming · 24 km W 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 44.8250, -110.4555. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Park County, MT | 71 km (44 mi) | N | earthquakes near Park County |
| Park County, WY | 78 km (48 mi) | ESE | earthquakes near Park County |
| Teton County, WY | 86 km (54 mi) | S | earthquakes near Teton County |
| Gallatin County, MT | 95 km (59 mi) | NW | earthquakes near Gallatin County |
| Fremont County, ID | 106 km (66 mi) | SW | earthquakes near Fremont County |
| Sweet Grass County, MT | 117 km (73 mi) | NNE | earthquakes near Sweet Grass County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
59 earthquakes have been recorded within 50 km since this one.
- 1.7 28 km S of Mammoth, Wyoming
- 1.7 27 km S of Mammoth, Wyoming
- 2.0 28 km S of Mammoth, Wyoming
- 2.3 36 km S of Silver Gate, Montana
- 1.6 37 km S of Silver Gate, Montana
- 1.9 37 km S of Silver Gate, Montana
- 2.1 28 km S of Mammoth, Wyoming
- 1.7 Wyoming
- 1.8 29 km S of Mammoth, Wyoming
- 1.6 29 km S of Mammoth, Wyoming
- 1.6 31 km ESE of West Yellowstone, Montana
- 1.6 32 km ESE of West Yellowstone, Montana
- 1.9 22 km S of Mammoth, Wyoming
- 1.6 47 km ESE of West Yellowstone, Montana
- 1.6 66 km ESE of West Yellowstone, Montana
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.