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NS11A-03 Stoneley waves and
Scholte waves in ground penetrating
radar (GPR) investigations.
Abstract
A well-known saying is that ground penetrating radar (GPR) is seismics with a
different excitation: electromagnetic instead of acoustic. The propagation paths
are the same, the data processing is mostly identical, and seismic evaluation
programs are equally used in the GPR evaluation. Without scale information,
radargrams cannot necessarily be distinguished from seismograms. We report on
another analogy between seismics and GPR interface waves, long known as
Stoneley and Scholte waves in seismics but rarely playing a significant role, which
we find are beginning to play an increasingly important role in GPR. Stoneley
waves are boundary waves travelling along a solid-solid interface, while Scholte
waves are propagating along a solid-fluid interface. Solid-air interface waves are
generally known as Rayleigh waves well known in seismics as typical surface
waves but may also join the Scholte and Stoneley waves in the context discussed
here. The boundary waves especially of the Scholte type came into our view by
peculiar observations during diverse GPR measurements over different geological
substrates with 200 and 300 MHz antennas and registration depths of the order of
10 m. The phenomenon: Occupation of the radargrams with mostly clearly
vertical, mostly sharply defined amplitude stripe patterns from single specimens to
regular or irregular cluster formations (see figure). Originally considered as a kind
of noise of inexplicable cause, this explanation could be excluded by the fact that
stripe patterns could be followed in measurements on parallel GPR profiles,
correlating meter by meter, and thus had to have their cause in the geological
subsurface. The conclusion from the known Scholte waves in the wall of water-
filled boreholes to groundwater-bearing open fractures/fissures in rocks was
obvious and short. Meanwhile, the GPR interface waves not only of the Scholte
type, but also the Stoneley waves have become an important geological tool in
addressing solid boundaries, for example, on faults or in fracture zones. The
extent to which Rayleigh waves can play a role in this context as solid-air interface
waves for distinguishing dry and water-bearing fractures/fissures/fracture zones
Monday, 12 December 2022
15:19 - 15:26
Online Only
remains subject to further investigation.
Plain-language Summary
We report on the observation of special boundary (interface) waves in ground
penetrating radar (GPR) measurements, which are well known in seismic
applications, but are largely unknown to occur in analog form in GPR
measurements of geologic subsurfaces. Investigation and interpretation of
fractures, fracture zones and faults are especially targeted.
First Author
E
Kord Ernstson
University of Würzburg
Author
P
Jens Poßekel
Geophysik Poßekel Hornhof 14, 45479 Mülheim
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