Geophones on a board

We examined the feasibility of using seismic reflections to image the upper 10 m of the earth's surface quickly and effectively by rigidly attaching g eophones to a wooden board at 5-cm intervals. The shallow seismic reflectio n information obtained was equivalent to control-test data gathered using c lassic, single-geophone plants with identical 5-cm intervals. Tests were co nducted using both a .22-caliber rifle source and a 30.06-rifle source. In both cases, the results were unexpected: in response to our use of small, h igh-resolution seismic sources at offsets of a few meters, we found little intergeophone interference that could be attributed to the presence of the board. Furthermore, we noted very little difference in a 60-ms intra-alluvi al reflection obtained using standard geophone plants versus that obtained using board-mounted geophones. For both sources, amplitude spec tra were ne arly identical for data gathered with and without the board. With the 30.06 source, filtering at high-frequency passbands revealed a wave mode of unkn own origin that appears to be related to the presence of the board; however , this mode did not interfere with the usefulness of the shallow-reflection data. The results of these experiments suggest that deploying large number s of closely spaced geophones simultaneously-perhaps even automatically-is possible. Should this method of planting geophones prove practical after fu rther testing, the cost-effectiveness of very shallow seismic reflection im aging may be enhanced. The technique also may be useful at greater reflecto r depths in situations employing bunched geophones. However, this approach may not be applicable in all circumstances because larger energy sources ma y induce interference between the geophones and produce undesirable modes o f motion within the medium holding the geophones.