Historic Earthquakes

Near Kosmo, Utah
1934 03 12 15:05:40 UTC
Magnitude 6.6
Intensity VIII

Largest Earthquake in Utah

This earthquake occurred in Hansel Valley, a sparsely populated area. Two people were killed. Property damage was limited mainly to downed chimneys and cracked walls in poorly constructed brick buildings. Chimneys were downed in several towns in the county, including Hooper, Kelton, Kosmo, Locomotive Springs, Monument, and Snowville. Large rockslides occurred at Aragonite, Lakeside, Monument Rock, and Snowville. An outstanding feature of this earthquake was the large quantity of water emitted from the craterlets and fissures that developed in the area.

Most of the ground cracks that formed in the epicentral area occurred in poorly consolidated rocks on the salt flats. These cracks were traced for a distance of more than 8 kilometers. Four distinct fractures, about 1 kilometer apart, developed across a road about 5 kilometers north of Kosmo. The vertical displacement along the fractures ranged from about 7.5 to 25.5 cm. Precise leveling surveys later revealed that areas of land sank as much as 39 cm. Horizontal displacement was not observed.

Many springs formed in the epicentral area. Most of them developed along well-defined fractures in the salt flats where water flowed along the fissure. Notable exceptions, however, were the springs that formed in Monument Rock where water flowed at individual centers and formed mud cones. In places, large holes developed around the springs by the caving of the soft material through which the water flowed. Two such holes on the salt flats northeast of Monument Rock ranged in diameter from 2.5 to 3 meters, and one was 11 meters deep. Also felt in Idaho, Montana, Nevada, 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.