Seismic survey method using shock wave reflections - employs linear array of blast holes at rectangular increasing depths and surface

摘要

The technique involves study of substrate beneath the earth's surface by the exploding shot at or near the surface detecting reflected shock waves by a number of surface geophones placed on the surface in a matrix array and analysing the results. Shot may be distributed in either a 2-dimensional or a 3-dimensional manner. The preferred method uses a linear track with shot exploded at steadily increasing vertical depths for equal horizontal spacings. Geophones placed in a surface rectangular matrix detect both direct and reflected waves; the frequency is typically 25 Kz and the vertical shot spacing 10m, and geophone lintes 60m apart. A distance/time plot for the response of a particular geophone from a particular shot line gives a linear result (1) for the direct signal, a curve (2) for the response from a fault tangential to the line at a point where the equivalent depth is found. An interference (Fresnel) zone is found (3) over a space/time region where the frequency interval is equivalent to half a wave length either side (4).