SEISMIC WEATHERED OR AERATED 
SURFACE LAYER! 
ONG) LESTER Re 
Tulsa, Oklahoma 
ABSTRACT 
The existence of a comparatively thin surface layer with a low velocity character- 
istic has been recognized in seismic work for several years, and has been generally 
referred to as the “ weathered layer.”’ This low velocity surface characteristic has been 
found to be almost universally present regardless of the nature of the surface deposits, 
and does not conform to the geologic weathering of the area. 
The purpose of the writer is to offer as an explanation of this phenomenon, the 
mixture of air in a free state with surface materials. Theoretical calculations, if the 
earth is assumed to be a fluid, indicate that velocities less than that of sound in air 
should be obtained from such mixtures. This is borne out by experimental data, as far 
as available, indicating that this so-called weathered layer might properly be termed 
an ‘“‘aerated”’ layer. 
It must be said at the outset that the conclusions of this paper are 
based on meager field data. The primary argument arises from theo- 
retical study and postulates certain effects. These effects, however, 
have been confirmed by experiment in so far as such experimental 
data are available. The purpose of the discussion is, first, to present a 
probable explanation of a phenomenon which has been recognized 
and dealt with—though unexplained; and second, as a result of such 
explanation, to suggest a more descriptive and less confusing name 
than that of “‘weathered.”’ 
The existence of a comparatively thin surface layer with a low 
velocity characteristic has been recognized in seismic work for several 
years, and it has been generally referred to as the “weathered layer.” 
This condition has been found to be almost universally present, re- 
gardless of the nature of the surface deposits, and has been recognized 
from its low velocity characteristic rather than by any physical or 
geological difference between it and the materials immediately below. 
The drilling of deeper shot holes, below the depth of this low velocity 
horizon, has failed to indicate any visible differentiation between it 
and adjacent materials. 
' Read before the Association at the Oklahoma City meeting, March 25, 1932. 
2 Geophysical Research Corporation, Box. 2040. 
60 
390 
