Eyewitness Account of Normal Surface Faulting

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Normal surface faulting associated with the Borah Peak, Idaho earthquake (preliminary Ms 7.3) of 28 October 1983 was witnessed in the vicinity of Arentson Gulch by two elk hunters, D. Hendriksen and J. Turner of Boise, Idaho. On the morning of the earthquake, the hunters were traveling in a four-wheel drive vehicle on a dirt road (Figure 1) with Hendriksen driving. Another pair of hunters, Mr. and Mrs. William Knox of Challis, Idaho, were on foot in the same area. Mr. Knox was to the northwest and on a hill above Hendriksen and Turner, and was driving elk toward his wife who was waiting near some power lines in a narrow valley (Figure 1). At 8:06 a.m. local time (14:06 UTC) the earthquake occurred, while Hendriksen and Turner drove their vehicle northeastward at a slow rate of speed (about 5 mph). A prominent fault scarp formed about 20 m directly in front of the vehicle, with the vehicle on the downthrown side (Figure 2). We interviewed Hendriksen and Turner at this site on the evening of 28 October and again at this site on the morning of 29 October. Hendriksen alone was interviewed at Boise State University on 8 November and 30 November. The 29 October interview and portions of the 8 November interview were tape-recorded and transcribed. Excerpts from these transcriptions and an interpretation of the events are given below. Observations made during the surface faulting by Mr. and Mrs. Knox are documented by Wallace (1984).


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