4-SHALLOW-DEPTH, SHEAR-WAVE FEASIBILITY STUDIES

Studies using a hammer-impact source were made to evaluate the feasibility of using shallow-depth, seismic shear-wave methods to (1) detect earth fissures, (2) map an anguiclude, (3) locate a bedrock channel, and (4) study the fault and fracture system within a highly fractured welded tuff. For detecting earth fissures, a V/V (vertical-impact, vertical-geophone-recording both P-waves and vertically polarized shear waves, SV), 6-m common-offset procedure was used; for mapping the aquiclude, an R/R (radial-impact, radial-geophone-recording predominantly SV), unbalanced-split-spread procedure; and for the bedrock channel search, a wide-angle, T/T (transverse-impact, transverse-geophone-recording horizontally polarized shear waves, SH) reflection procedure. The principal result of these investigations is that it is technically feasible through use of shear-wave methods to obtain reasonable solutions to the first three problems. For the tuff study, wave tests showed phase velocity differences between R/R and T/T recordings indicating shear-wave splitting, and revealed a fault between blocks of seemingly similar lithology.