Improving ultrashallow seismic reflection data by reducing source energy

Abstract

Summary Ultrashallow seismic reflection (USR) surveying—used to gather information within the upper few meters of the subsurface—is a critical resource when reflection-scale resolution is necessary but surface conditions limit the use of ground-penetrating radar (GPR). However, acquiring highquality USR data requires specialized sources. To ascertain the important features of such sources, experiments were conducted using various impulsive seismic sources (4.5-kg hammer, 30.06 rifle, and .22-caliber rifle) to examine the effects of minimizing source energy on the frequency content of reflection data. Results indicate that the higher energy sources (e.g., sledgehammer, large-caliber projectiles) lack some of the high-frequency energy exhibited by smaller sources, precluding the detection of reflection signal from less than 3-m-depth at the sites tested. Additionally, the .22-caliber rifle yielded more energy above 250 Hz than either the sledgehammer or 30.06 rifle, and the .22-caliber rifle with subsonic ammunition yielded the largest amount of energy at frequencies above 300 Hz and produced the best USR data at both test sites.