Models of Deep Geoelectric Structures - Models and Methods of Magnetotellurics - page 289

the epicentre of the crustal conductive zone, while the imaginary induction arrows
reverse their direction in the transition from the high frequencies to the low ones.
How are the real and imaginary tippers influenced by dimension of a crustal
conductive zone and its resistivity? Fig. 8.11 presents curves for Re W zy and
Im W zy measured over the right edge of the conductive prism with half-width
ν = m. It is seen that narrowing the prism

from 1000 km to 50 km and increasing its resistivity from 10 to 50 Ohm

25 , 500 km and c = 10 , 25 , 50 Ohm ·

mwe
substantially diminish the real and imaginary tippers, but they still are measurable.

·

8.1.3 Electromagnetic Excitation of Crustal Conductors

Two physical mechanisms, galvanic and inductive, may be implicated in the
electromagnetic excitation of the three-dimensional crustal conductors.
The galvanic mechanism is associated with electric currents that percolate from
sediments and concentrate within the crustal conductive zone. The resistive crustal
layers underlying the sediments hamper the current redistribution and screen the
conductive zone. Intensity of the galvanic excitation can be estimated by the adjust-
ment distance d

= √ S sed R cr ust , where S sed is the sediments conductance and R cr ust

Fig. 8.11 Real and imaginary tippers over the right edge of wide ( v = 500 km) and narrow ( v =

25 km) crustal conductive zone of resistivity = 10 , 25 , 50 Ohm · m . The model is shown in

c

2 = 2 = h 2 = Fig. 8.3. Model parameters: = 10 Ohm · m , h 1 = 1km, 1000 Ohm · m , 19 km , 1

h 2 = ,

2

h 2 = 15 km = 500 Ohm · m , 65 km , = 10 Ohm · m 3