The March 31, 1973 earthquake
M5.1near West Yellowstone, Montana, Wyoming
A magnitude 5.1 earthquake 6.2 miles deep, centred in Teton County. The 10th strongest in Wyoming’s record since 1900, and the strongest within 50 miles since a magnitude 6.3 on August 18, 1959. 3 aftershocks of magnitude 2.5 or more followed within 30 days.
The earthquake
- Magnitude
- 5.1
- body-wave magnitude (mb)
- Depth
- 6.2 mi
- 10.0 km below the surface
- Local time
- Saturday, March 31, 1973
- 13:33 MST; 20:33 UTC
- In Wyoming’s record
- 10th
- strongest of 1,557 since 1900
USGS ANSS Comprehensive Earthquake Catalog, event usp0000163 (“51 km ESE of West Yellowstone, Montana”). The USGS event page carries the ShakeMap, felt reports and the official summary.
Aftershocks
Earthquakes of magnitude 2.5 or more within 20 miles of the epicentre in the 30 days after.
3
Aftershocks in 30 days
4.4
Largest aftershock, Apr 21, 1973
0
On the first day
6
In the 7 days before
- The search radius is the surface rupture length expected for an earthquake of this magnitude (Wells and Coppersmith, 1994), at least 20 and at most 600 miles, so a great earthquake's sequence is counted along its whole fault.
Counties and cities within 50 miles
Distance from the epicentre to each county boundary (zero when inside) and to each city centre.
Counties
- Teton CountyWY · inside
- Park CountyWY · 6.3 mi
- Fremont CountyID · 27.6 mi
- Gallatin CountyMT · 27.8 mi
- Fremont CountyWY · 41.1 mi
- Park CountyMT · 43.3 mi
- Teton CountyID · 45.8 mi
- Madison CountyMT · 46.6 mi
- Sweet Grass CountyMT · 47.3 mi
- Carbon CountyMT · 47.9 mi
- Beaverhead CountyMT · 48.0 mi
Earthquakes around the epicentre
349 earthquakes of magnitude 3 or more within 50 miles of this epicentre since 1973.
Earlier earthquakes of magnitude 5 or more within 50 miles, strongest first
- August 17, 1959M7.2
- August 18, 1959M6.5
- August 18, 1959M6.3
- August 18, 1959M6.0
- August 18, 1959M5.7
- August 19, 1959M5.0
- March 27, 1973M5.0
USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.