The shock measured 6.9 on the moment magnitude scale and had a maximum Mercalli intensity of IX ( '' Violent '' ) . It was the most violent earthquake in the lower 48 states in over 24 years , since the 1959 Hebgen Lake earthquake in nearby southwestern The earthquake was caused by a slip on the preexisting Lost River Fault
1959 Hebgen Lake earthquake
1959 Hebgen Lake earthquake
1983 Borah Peak earthquake