We have identified and described two different forms of electrical energy that may be created by the standard hammer-on-metal-plate seismic source option. The motion of the metal plate itself creates an electric field, which we refer to as the Lorentz field, due to the physics implied by Equation (3). The second effect is electrokinetic in origin, and is termed the ``direct field''. It is the field of the electrical charge separation caused by the asymmetrical pressure gradient created at an impact source (such as a sledgehammer).
The Lorentz field is unlikely to prove useful, and so is a noise source to be avoided. Fortunately this can easily be achieved with the use of a non-metal hammer plate, or insulation between a metal plate and the earth.
The direct field could potentially be used to measure physical properties of the region where it exists (immediately around the source). Though not terribly interesting at the surface, measurement of the direct field in a down-hole setting could prove useful.