Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

The in-phase induction arrow is defined by (in Parkinson's sense of
orientation) by
h
p = - R&(x A + B]
and the ou-t' of-phase arrow by
q + Imagl; A + Bl
h h
where x and y are unit vectors in x- and y-direction. General-ly
speaking, the in-phase arrows point toidards internal concentrations
of induced currents, i.e. to zones of lower than "normal" re-
sistivi.ty at one particular depth.TheYmay point also away from high
resistiv:ity zones around which the induced currents are diverted.
Vertical soundings with station arrays:
The resistivity structure is regarded as layered, p = p(z),but the
inducing source field as non-uniform. Inducing and induced fields
will have ms.tching wave-number spectren with well defined ratios
between spectral components in accordance to the subsurface re-
s i s t ivi-ty structure . h ea-t-k-+h~++t-~o-~~&e-~~idc~~~
e.ve;i:~-~:gh-i-s-k~ol.a-7,-u~.-f m~rnGty--rnaap-~be--~i-~-~P+f+a
Let U and V be field components of the surface field in the frequency
distance domain: U = UCw ,R) , V = VCw ,R). They are deco~nposed into
h h A
the wave-number spectren U(w,k), VCw,k) according to
with
irnh ikR - -
U(w,R) = I I UCw,L,)e dk dk
- '0 Y X