HAMMER REFLECTION SEISMICS IN ENGINEERING GEOPHYSICS

Abstract

A major problem in exploiting the reflection method in engineering geophysics lies in the difficulty of separating the various superimposed arrivals at short record times. Velocity filtering is used in the present study as a means of identifying the reflection arrivals by removing the undesirable waves and leaving a substantially usable reflection record, even at very short record times. Special circuitry has been developed to sense the time lag of positive zero crossings of the signal at two separate geophones, and to record only those arrivals whose phase shift is smaller than an arbitrarily set amount. This circuitry has been incorporated into a standard hammer‐type engineering seismograph. Fundamentals of analysis of an expanding reflection spread are reviewed, and field examples are shown to demonstrate the abilities and limitations of the present technique.