P. Schmoldt, PhD - MTNet - DIAS

10. Data inversion
Depth (km)
Depth (km)
(a)
(b)
S N
Campo de Montiel M.P.
Loranca Basin
0
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100
150
200
250
300
0
50
100
150
200
250
300
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0 16 32 48 64 80 96 112 128 144
Distance (km)
log 10
(Wm)
0 1.1 2.2 3.3
Fig. 10.21.: Models of electric resistivity distribution beneath the Tajo Basin using an anisotropic 2D inversion approach. Models
are obtained using the MT2Dinv inversion algorithm [Baba et al., 2006] with electric resistivity gradient regularisation, smoothing
parameters α = 3, β = 1, τ = 6, and starting models shown in Figure 10.19 (with the same letters). Inversion models obtained using
either starting model are virtually identical and exhibit a RMS misfit of 3 with error floors of 20% and 10% for ρa and φ, respectively.
charge transport mechanism and do not take into account contributions of electronic or
electrolytic conductivity (cf. Sec. 5.1). Hence, resistivity values in the lithosphere, where
other conduction mechanisms are likely to have a significant contribution, may be overestimated
by this approach. Moreover, electric resistivity values of the asthenosphere are
likely to be higher than denoted by the reference profiles, i.e. in the range of 100 Ωm (or
5 – 25 Ωm for an electrically conductive uppermost asthenosphere; cf. Section 5.2.2).
The eLAB is commonly assumed to coincide with the transition from resistive lithospheric
mantle values of ≥1000 Ωm to values of approximately 100 Ωm for a dry asthenosphere
5 . The change of the electric resistivity gradient is associated with the transition
from conduction to convection as the dominant heat-transport mechanism at the LAB and
the resulting changing slope in the mantle geotherm. Since electric resistivity of Earth
materials is profoundly affected by temperature (cf. Sec. 5.1), the LAB is likely to be
associated with a similar change in the ρ – depth profile. Despite lateral varying average
electric resistivity values, denoted by the differences between ρ – depth profile of the
5 Water, partial melt, or grain-size variation along the eLAB may cause significant further reduction of
resistivity in the uppermost asthenosphere; cf. Section 5.2.2
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