Earthquakes in the Intermountain West are a mountain-building process as rock moves vertically along a fault. Earthquakes typically occur repeatedly along the same faults. Arrows in this photo point out the new fault scarp face (~9 feet tall) created in the 1983 Borah Peak, ID earthquake. It is superimposed on an ancient fault scarp (vegetated, beveled area immediately above new scarp).

1983 Borah Peak, ID earthquake: magnitude 7.3

Luckily there were no buildings astride the new fault scarp. The only man-made structure affected was the Doublespring Pass Road.

1983 Borah Peak, ID earthquake: magnitude 7.3

The direction of movement along the fault was predominantly vertical, but the broken drainage ditch shows that some lateral movement also occurred.

1983 Borah Peak, ID earthquake: magnitude 7.3

Two friends were elk hunting in the epicentral area when the earthquake occurred. Rock fall and road damage made driving out impossible. They hiked 5 miles to Heard Lake where a ranger was looking for them.

1983 Borah Peak, ID earthquake: magnitude 7.3

Close call! The people living in this house near the base of steep cliffs in Challis, Idaho, were very grateful that the ~20-ton boulder that fell during the earthquake came to rest "next to" rather than "on top of" their home.

1983 Borah Peak, ID earthquake: magnitude 7.3

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