Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

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Model : wo+ Solution for uniform half-space: CI = CII = lk( (a = oO) Recurrence formula foY layered half-space'{Cn = C(zn)}: - C~~ - C~~~ = Jioy o + [kr2 0 L The TE-field within the n'th layer at the depth z = zn + E, Z < Z + E < Z n+l' can be calculated from its surface value n n according to: with gtzr,zs) = cosh Bps - sinh Brs/(K,Cr) h(zr,z ) = cosh @, - sinh B K C s rs r r for s.< - n and gCzn, z~+E) = cosh(Kn~)-sinh(K n E)/K n C n

, , The formula for E applies also to E and HZ, the formula for X Y Hx also to H . Y 7.4 Penetration depth of various types of geomagnetic variations and the overall distribution of conductivity within the Earth Three types of conduction which vary by orders of magnitude have to be distinguished: 1. Conduction through rock forming minerals 2. Conduction through fluids in pores and cracks between rockfor- mine minerals 3. Metallic conduction li: Since the minerals of crustal and mantle material are expected to be silicates, the conduction through these minerals will be that of semi-conductors. Their resistivity is in the order 5 of 10 Om at room temperature but decreases with temperature T is the absolute temperate, k Boltzmann's constant; a and A 0 are pressure-dependent and composition-dependent constants within a limited temperature range, for which one specific mechanism of semi-conduction is predominant. Hence, in plots of in o versus T-' the o-T dependence should be represented by joining segments of straight lines. Laboratory experiments with rocks and minerals at high temperature and varying pressure have confirmed this piece-wise linear dependence of lno from T-l. Furthermore, they showed that the composition- dependence of u is mainly contained in the pre-exponential

, ,<br />

The formula for E applies also to E and HZ, the formula for<br />

X Y<br />

Hx also to H .<br />

Y<br />

7.4 Penetration depth of various types of geomagnetic variations<br />

and the overall distribution of conductivity within the Earth<br />

Three types of conduction which vary by orders of magnitude have<br />

to be distinguished:<br />

1. Conduction through rock forming minerals<br />

2. Conduction through fluids in pores and cracks between rockfor-<br />

mine minerals<br />

3. Metallic conduction<br />

li: Since the minerals of crustal and mantle material are expected<br />

to be silicates, the conduction through these minerals will<br />

be that of semi-conductors. Their resistivity is in the order<br />

5<br />

of 10 Om at room temperature but decreases with temperature<br />

T is the absolute temperate, k Boltzmann's constant; a and A<br />

0<br />

are pressure-dependent and composition-dependent constants<br />

within a limited temperature range, for which one specific<br />

mechanism of semi-conduction is predominant. Hence, in plots<br />

of in o versus T-' the o-T dependence should be represented<br />

by joining segments of straight lines. Laboratory experiments<br />

with rocks and minerals at high temperature and varying<br />

pressure have confirmed this piece-wise linear dependence of<br />

lno from T-l. Furthermore, they showed that the composition-<br />

dependence of u is mainly contained in the pre-exponential

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