SHALLOW STRUCTURE FROM A SEISMIC-REFLECTION PROFILE ACROSS THE BORAH PEAK, IDAHO, FAULT SCARP

Abstract. A short 12-fold CDP seismic-reflec- compared to depths of 50-650 m for MiniSOSIE tion survey was performed along the road to data. They both are good locators of major Doublespring Pass across the fault scarp formed by faulting. The two reflection techniques are the October 28, 1983, magnitude-7.3, Idaho earth- sufficiently different in resolution that, except quake. This high-resolution reflection survey was for imaging the major faults, practically no conducted to determine the feasibility of using reflection seismology to delineate shallow struc-tures in a fault zone. Field-recording parameters were designed to optimize seismic reflections in the 30-150 msec range corresponding to 10-100 m in depth. A modified 30-06 hunting rifle was used as the energy source. Single 100-Hz geophones at 1.5-m group intervals in conjunction with 220-Hz low-cut recording filters (24 dB/octave) provided dominant frequencies above 150 Hz on fiel