Table 7.4.

Summary of the geophysical responses associated with different particle sizes of geological materials

TechniqueFinesSandGravelDiamicton
Ground-penetrating radarAttenuation of the signal and loss of data.
Lower frequency antennas may provide some reflectors if fines are underlain by a more coarse grained unit (e.g. Fig. 7.13)
High-amplitude reflections occur at interfaces between materials with different physical properties, for example beds of coarse and fine sands.Hyperbola from large point sources such as cobbles/boulders, which can also cause scattering and attenuation of signal. High-amplitude reflections occur at interfaces between materials with different physical properties in smaller gravels (e.g. pebble/granule size)Varied response depending on composition of diamicton. A diamicton comprising a fine-grained matrix with larger point sources would be characterized by signal attenuation with possibly some hyperbola from large point sources.
ResistivityLow resistivityVariable depending on amount of pore fluid within the material. Typically higher resistivity than fines even when saturated.High resistivityVaried response depending on composition of diamicton. A diamicton with a fine-grained matrix with larger point sources would be characterized by a typically higher resistivity than a fines material, with values overlapping those of sand.
ConductivityHigh conductivityDepends on amount of pore fluid within the material. Typically lower conductivity than fines even when saturated.Low conductivityVaried response depending on composition of diamicton. A diamicton with a fine-grained matrix, with larger point sources, would be characterized by a typically lower conductivity than a fines material, with values overlapping those of sand.
Seismic reflectionReflections occur at interfaces between materials with different physical properties.Reflections occur at interfaces between materials with different physical properties, for example beds of coarse and fine sands.Hyperbola from large point sources such as cobbles/boulders, which can also cause scattering and attenuation of signal. High-amplitude reflections occur at interfaces between materials with different physical properties in smaller-sized gravels (e.g. pebble/granule size)Varied response depending on composition of diamicton. A diamicton comprising a fine-grained matrix with larger point sources would be characterized by signal attenuation with perhaps some hyperbola from large point sources.
Seismic refractionHigh velocities through material due to stiffness:
P-wave 1000–2500 m s−1;
S-wave 400–1000 m s−1
Moderate velocities through material:
P-wave 200–2200 m s−1
S-wave 80–880 m s−1
Slow velocities through material:
P-wave 400–1000 m s−1;
S-wave 230–550 m s−1
Varied response depending on composition of diamicton. A diamicton comprising a fine-grained matrix with larger point sources would have lower velocities than fine materials, and overlapping those of sand/gravel.