The October 21, 1964 earthquake

M5.2near Hebgen Lake Estates, Montana

A magnitude 5.2 earthquake 6.2 miles deep, centred in Madison County. The 19th strongest in Montana’s record since 1900, and the strongest within 50 miles since a magnitude 6.0 on August 18, 1959.

The earthquake

Magnitude: 5.2; moment magnitude (mw)
Depth: 6.2 mi; 10.0 km below the surface
Local time: Wednesday, October 21, 1964; 00:38 MST; 07:38 UTC
Epicentre: 44.88°N, 111.57°W; In Madison County
In Montana’s record: 19th; strongest of 1,459 since 1900
Within 50 miles: 8; counties; more on this date

USGS ANSS Comprehensive Earthquake Catalog, event iscgem863737 (“32 km WNW of Hebgen Lake Estates, Montana”). The USGS event page carries the ShakeMap, felt reports and the official summary.

Counties and cities within 50 miles

Distance from the epicentre to each county boundary (zero when inside) and to each city centre.

Counties

Madison CountyMT · inside
Fremont CountyID · 12.1 mi
Beaverhead CountyMT · 12.5 mi
Gallatin CountyMT · 12.7 mi
Clark CountyID · 22.7 mi
Park CountyWY · 26.4 mi
Park CountyMT · 26.9 mi
Teton CountyWY · 29.0 mi

Earthquakes around the epicentre

400 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

USGS ANSS Comprehensive Earthquake Catalog. Local time is the time zone of the county nearest the epicentre. Magnitudes are as the catalogue reports them.