On Some Problems Concerning the Seismic Field Methods

Abstract

The periods of longitudinal waves produced by explosions increase with distance in a similar way as earthquake waves (equation 1). The amplitudes of the waves (equation 1) depend not only on the amount of energy reflected or refracted at discontinuities, but also on the angle of incidence at the instruments and its rate of change with distance. Calculations on the relative amplitudes of direct, reflected and refracted waves (Fig. 1) are in agreement with the observations. Formulae are given to calculate the approximative dip of discontinuities using either the distance at which the travel time of the reflected wave is a minimum or the difference in travel time between two instruments, especially at two opposite sides of the shot point, or the direction of the travel time curve at the shot point. The surface waves (ground roll) recorded from explosions can hardly be pure elastic waves; their velocity is too small for either Love- or Rayleigh-waves.