Source-dependent frequency content of ultrashallow seismic reflection data

seismic surveying within the upper few meters of the Earth's shallow subsur face requires a high-frequency source. To ascertain the important features of such sources, experiments were conducted at test sites in central and ea stern Kansas using various impulsive seismic sources (4.5-kg hammer, 30.06 rifle, and .22-caliber rifle) to examine the effects of minimizing source e nergy on the frequency content of reflection data. Results indicate that th e higher energy near-surface seismic-reflection sources (e.g., sledgehammer , large-caliber projectiles) lack some of the high-frequency energy exhibit ed by smaller sources, precluding the detection of reflection signal from u ltrashallow depths (<3 m) at the sites tested. At the test site in eastern Kansas, the .22-caliber rifle yielded more energy above 250 Hz than either the sledgehammer or 30.06 rifle. At the test site in central Kansas, where three reflective interfaces shallower than 3 m exist, the .22-caliber rifle with subsonic ammunition yielded the largest amount of energy at frequenci es above 300 Hz and produced the best data.