P. Schmoldt, PhD - MTNet - DIAS

5.3. Parameters controlling the conductivity of the Earth’s mantle
Element Formula Composition
Iron Fe 88.8
Nickel Ni 5.8
Sulphur S 4.8
Tab. 5.6.: Composition of the Earth’s Core; from Morgan and Anders [1980].
by the large earthquake near New Zealand in 1929. This hypothesis was subsequently
supported by various authors [e.g. Gutenberg and Richter, 1938; Jeffreys, 1939; Birch,
1952; Jacobs, 1953] before it became widely accepted in 1971 when Dziewonski and
Gilbert published the results of their studies on normal mode vibrations of the Earth due
to large earthquakes.
The composition of the core
The Earth’s core consists mainly of iron with a smaller amount of nickel and sulphur, and
is most likely a Fe-FeS alloy [Morgan and Anders, 1980; Sherman, 1995]. Lab studies,
intended to determine the composition of the Earth’s core, suffer from the requirement
to reproduce the P-T conditions; i.e. 140 – 360 GPa and 4000 – 7000 K [Dubrovinsky
and Lin, 2009]. Therefore, type and proportion of minor constituents are still under debate;
the presence of silicon, oxygen and sulphur is suggested by mineral physics studies
[Badro et al., 2003] (cf. Tab. 5.6). Due to the high amount of metallic components, the
conductivity of the Earth’s core is dominated by electronic conduction. Electric properties
of the Earth’s core cannot be investigated with the MT or GDS method due to
its enormous distance from the Earth’s surface where measurements are made [e.g. Xu
et al., 2000a]. Despite its high content of conductive material, recording times of several
decades are needed to identify signals of the Earth’s core in MT data [Rikitake, 1952].
Furthermore, any data with sufficiently long periods to detect the boundary of the core
would suffer from the very short induction depth caused by the high conductivity of the
materials within, making investigations of the core’s internal structure virtually impossible
(cf. Section 3.3 for details on induction depth). Therefore, investigations of the
Earth’s core are usually limited to Geodynamic modelling [e.g. Glatzmaier and Roberts,
1995; Glatzmaier, 2002; Turcotte and Schubert, 2002].
5.3. Parameters controlling the conductivity of the
Earth’s mantle
Conductivity variations in the Earth’s mantle (Sec. 5.2.2) are, besides changes in composition,
mainly due to changes in pressure, water content, and especially temperature.
Modern estimates of temperature–depth and pressure–depth profiles are considered rea-
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