U.S. Geological Survey Crustal Studies Technical Letter Number 17
A study of first-arrival amplitudes from 6 water shotpoints and 7 drill-hole shotpoints in parts of central and western United States indicate a variation of over 100 to 1 between the best and poorest shotpoints.
Water shotpoints are, in general, superior to drill-hole shotpoints; however, one drill-hole shotpoint produced higher signal amplitudes than more than half of the water shotpoints. Signal amplitudes from drill-hole shotpoints varied by a factor of over 20. Saturated clay shooting medium appears to be the best shooting medium. Amplitudes from water shotpoints varied by a factor of about 10. Signal amplitude increases, in general, with water depth for bottom shots.
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Jackson W.H., and Healy, J.H., 1964, Preliminary report on some factors affecting shotpoint efficiency: U.S. Geological Survey Crustal Studies Technical Letter Number 17, 23 p. (Available at https://pubs.usgs.gov/misc/tl/0017/.)