GROUND ROLL COUPLING TO ATMOSPHERIC COMPRESSIONAL WAVES

Abstract

A theoretical treatment of ground roll originating from air shots and hole shots is given. It is shown that coupling of ground roll to compressional waves in the atmosphere exists for both air shots and hole shots. Experimental data obtained in the field are in excellent agreement with the theoretical results; namely, that the effective coupling exists for surface waves whose phase velocity is equal to the speed of sound in air. In regions where Rayleigh wave velocities vary with period due to layering in such a way that they are less than the speed of sound in air for short periods and exceed this value for longer periods, this coupling gives rise to a unique surface wave pattern on seismic records. It is shown that body wave and surface wave character is almost independent of charge elevation in the range from 0 (on the ground) to 30 feet. In a reciprocal manner ground roll from hole shots was recorded with air microphones as predicted by the theory.