Electroseismic data may show two different forms of source-related energy. The first is the electroseismic direct field which is produced at any impact source. It is approximately an electric dipole created by the asymmetrical pressure field of the impact. The second field is the electric field created by the impact of a mass on a metal hammer plate. The impact moves the hammer plate within the earth's magnetic field, and creates an electric field described by Lorentz's equation. Both show no moveout, and the amplitude pattern of a dipole. The direct field may be differentiated from the Lorentz field, however, by its reversed polarity on opposite sides of the shot point.