The Borah Peak, Idaho Earthquake of October 28, 1983—Isoseismal Map and Intensity Distribution

Abstract

The Borah Peak, Idaho, earthquake of October 28, 1983, caused two deaths in Challis and injured one person in Mackay. The most severe damage occurred in Mackay and Challis, where 11 businesses and 239 homes were damaged. Maximum Modified Mercalli intensity of VII was rated for both Challis and Mackay based on damage due to vibrational effects. Intensity IX was assigned to the area along the 34-kilometer-length of surface faulting. This event is comparable to the 1959 Hebgen Lake, Montana, earthquake, which was assigned an intensity X based on geologic effects and VII - VIII on vibrational effects (Steinbrugge and Cloud, 1962). The Borah Peak event was felt over 855,000 km2 of the United States and Canada.