March 28, 1975 Earthquake: Pocatello Valley, Idaho, United States
A magnitude 6 earthquake struck Pocatello Valley, Idaho, United States on March 28, 1975 at 02:31:05 UTC, 5 km below the surface.
Map
Where it struck, with the other significant earthquakes within 200 km. Circles are sized and colored by magnitude; select one for its page.
The earthquake
- Date
- March 28, 1975
- Time
- 02:31:05 UTC
- Place
- Pocatello Valley, Idaho, United States
- Magnitude
- 6 (Ms)
- Magnitude scales
- Ms 6 · mb 6.1 · ML 6.2 · Unspecified 6.2
- Focal depth
- 5 km (3 mi)
- Intensity
- VIII, severe shaking, on the Modified Mercalli scale
- Tsunami
- None recorded
- Epicenter
- 42.060° N, 112.550° W
- Country
- United States
- Region
- North America and Hawaii
- USGS record
- The USGS’s page for this earthquake
Ms: surface-wave magnitude. mb: body-wave (P-wave) magnitude. ML: local magnitude, the original Richter scale. Unspecified: the method was not stated in the published sources. NCEI’s headline magnitude is the best of these for the earthquake.
The toll
- Injuries
- 1
- Damage
- $1 million
- Houses damaged
- 520
Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.
What happened
The USGS’s account of the effects of this earthquake.
Maximum observed Modified Mercalli Intensity (MMI) VIII
In the Ridgedale area of the sparsely populated Pocatello Valley, this earthquake shifted several ranch houses on their foundations and toppled many chimneys. At Malad City, 20 kilometers northeast of the epicenter, about 40 percent of the chimneys on old buildings were damaged. Total property damage was estimated at $1 million.
Geologists observed one zone of ground fractures - about 0.6 kilometers long and 5 centimeters wide - in the south-central section of the valley. The shock triggered many snow avalanches northeast of the valley. Fourteen aftershocks ranging in magnitude from 3.8 to 4.7 were located through March 31. Felt in parts of Colorado, Idaho, Nevada, Utah, and Wyoming.
Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.
From the USGS event page for usp0000ad8. U.S. Geological Survey text and figures are in the public domain.
Magnitude estimates
The magnitudes the USGS catalog lists for this earthquake, by scale and by who computed them. NCEI’s own scales are in the table above.
| Mag. | Scale | Computed by | Notes |
|---|---|---|---|
| 6.1 | mb, body-wave | USGS National Earthquake Information Center | Preferred · Reviewed |
| 6.07 | Mw, moment | ISC-GEM global catalog | Final · ±0.3 |
| 6.14 | Mw, moment | USGS historic United States catalog | Final |
What the record says
NCEI’s account, from the sources it cites.
Shaking from the earthquake was reported felt as far north as Idaho Falls, Idaho, as far south as Richfield, Utah, as far east as Rock Springs, Wyoming, and as far west as Wells, Nevada. However, the greatest amount of property damage occurred in Malad City, located about 40 miles from the epicenter. The damage in Malad City was widespread-almost every home and building was affected. An April 11 newspaper report noted that 520 homes and 26 businesses were damaged by the earthquake shaking with seven homes completely destroyed.
No deaths were reported in connection with the earthquake. There was one reported injury consisting of minor cuts and bruises caused by a falling roof panel.
In the Pocatello Valley, seasonal-use buildings showed damage
The earthquake caused a broken water main in Bothwell, Utah.
(all above from reference #12600)
Sources NCEI cites
The publications NCEI lists for this record. The numbers match the “reference #” notes in its account above.
- #1053 National Earthquake Information Center (NEIC) (1971 to 2013). Preliminary Determination of Epicenters (PDE), a weekly and monthly publication, National Earthquake Information Center, U.S. Geological Survey, Golden, Colorado, 1971 to 2013.
- #12600 University of Utah (2020). Intermountain Seismic Belt Historical Earthquake Project, U of U Seismograph Stations. Accessed 14 January 2020. Link
- #1167 Rothe, J.P. (1974-1975). Annual Summary of Information on Natural Disasters, UNESCO, Paris, France, no. 9 (1974, missing from archives) and no. 10 (1975), 107 p.
Other significant earthquakes nearby
Within 200 km, the deadliest first.
More
Significant earthquakes of 1975The 1900sEvery quake the USGS located in 1975Recent earthquakes near hereThis day in weather history
Sources
Significant earthquakes from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-10-01. NCEI earthquake 4687. The written accounts and the magnitude estimates are from the USGS earthquake catalog, event usp0000ad8, matched to this record by time, place and magnitude.