Three-dimensional in-situ subsurface density estimations and the seismic skin depth

Abstract

All electromagnetic geophysical methods, but the frequency domain methods in particular, depend on the skindepth as a guide to the depth of investigation or penetration from the surface. By definition the skindepth is the distance where the initial amplitude of the electromagnetic wave attenuated by 1/e or 67%. This measure is influenced by the physical properties of the subsurface and uses the resistivity, the angular frequency (w) of the electromagnetic field and the magnetic permeability (m). By using more than one frequency, different depths of penetration are achieved, which allows one to obtain information from the consecutive different layers of geology. The same is true of seismic waves which also attenuate with distance and time. The attenuation also depends on the properties of the subsurface, of which the frequency (f), velocity (v) and the Q-factor are the most important. Similar to the electromagnetic method, depth of penetration can be manipulated in a way by controlling the frequency of the input wave. This information can be used in conjunction with this spreadsheet to design seismic surveys