Geoscience Reference
In-Depth Information
Quadrature conductivity:
Imaginary part of the complex
electrical conductivity. It corresponds to the reversible storage
of electrical charges at low frequencies in porous rocks. This
component is measured in geophysics through the induced
polarization method.
Richards equation:
Field partial differential equation for the
pressure of thewater phase in unsaturated condition. The valid-
ity of this equation is based on the assumption that the nonwet-
ting phase is very compressible and at constant (atmospheric)
pressure.
Reynolds number:
Dimensionless ratio between the inertial
and viscous term in the Navier
Stern layer:
Inner portion of the electrical double layer corre-
sponding to ions that are weakly or strongly sorbed on the
mineral surface.
Streaming current:
Source current generated by the flow of
the pore water and the drag of the excess of electrical charges
contained in the pore water because of
the electrical
diffuse layer.
Tortuosity:
The tortuosity of the pore space of a porous material
describes the relative path in a given direction imposed by the
topology of the pore network with respect to the straight
direction. Different tortuosities can be defined for different
transport properties because of the local boundary condition
problem defining these properties.
Undrained:
An undrained mechanical behavior describes
the behavior of a porous material when the fluid has no
time or cannot flow through the connected pore space. In
this case, the fluid resists to the deformation of the elastic
skeleton (frame) of the porous material.
Vadose zone:
Unsaturated portion of the ground comprised
between the ground surface and the water table of an uncon-
fined aquifer. The saturation of the water phase is smaller
than one.
Water wet:
A porous material is water wet if the water has a
preferential wettability (affinity) for the solid phase.
Water table:
Interface between the vadose zone and an uncon-
fined aquifer where the porous material is at saturation and
the water at atmospheric pressure.
Zeta potential:
Microscopic electrical potential of the electrical
double layer at the position of the shear plane, typically
between the Stern layer and the diffuse layer.
Stokes equation.
Seismogram:
Record of the ground motion at a measuring sta-
tion as a function of time. Seismograms typically record
ground motions in three Cartesian axes. The seismic source
can be an artificial source or a natural source such as an
earthquake.
S-wave:
Shear or secondary elastic wave characterize by a
motion normal to the direction of propagation. This wave does
not diverge (the divergence of the displacement is equal to
zero). This type of wave does not travel through a viscous fluid.
Seismoelectric effect:
Geophysical method in which seismic
waves propagate in the ground and the associated electromag-
netic effects are measured. The coupling is electrokinetic in
nature.
Self-potential:
Passive geophysical method consisting in mea-
suring the electrical field at the ground surface (possibly in
boreholes) in order to retrieve the causative source of current
in the subsurface.
Skeleton:
The skeleton denotes the solid frame of a porous
material.
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