P. Schmoldt, PhD - MTNet - DIAS

9. Data collection and processing
constraint at greater depth given their limited period range and larger errors. The multistrike
analysis yields directions of N30.0E and N29.4E (0.8 av. RMS misfit) for the Tajo
Basin of the lithospheric-mantle with depth down to 100 km and 120 km, respectively; as
well as a direction of N20.2E (0.7 av. RMS misfit) for the asthenosphere.
The significantly different values indicate that the geoelectric strike below the Tajo
Basin varies between lithospheric and asthenospheric parts of the mantle, and that the
LAB is likely to be found at depth below 120 km. The latter assumption is based on the
fact that the observed strike direction is similar for the depth ranges with and without
the interval 100 – 120 km, indicating that this interval agrees with structures of the region
above. This observation, however, is not well constraint since structures for such a thin
layer at this depth are not well resolved. The true strike directions for the lithosphericmantle
can be assumed to possess an orientation between 0 and 90 degrees, rather than
the orthogonal direction, considering the results of seismic tomography studies in this
regions, indicating a NE-SW geological strike (cf. Section 7.3.2).
Lithospheric depth
Finally, despite indications for different strike directions of crust and mantle by previous
analyses and seismic results (cf. Sec. 7.3.2), it is tested whether a reasonable, common
strike direction can be found for the depth range spanning from intermediate crust to
LAB. The multi-strike analysis yields a direction of N37.2E (1.1 av. RMS misfit) and
N35.3E (1.1 av. RMS misfit) for the Tajo Basin lithosphere with an assumed LAB depth
of 100 km and 120 km respectively; coincident with a range of low RMS misfit in the
main plot of Figure 9.11. For the whole profile a direction of N15.0E is determined,
which however does not fit with the RMS distribution of stations in the Betic Cordillera.
In principle, a common geoelectric strike direction of intermediate crust, lower crust and
lithospheric-mantle can be found: However, certain aspects favour a separate treatment of
the two regions, namely the higher average RMS misfit for the combined range indicating
an inferior fit of local structures and, more importantly, results of the other geophysical
methods that are in favour of two different strike directions at crust and mantle depths (cf.
Sec. 7.3.2).
Conclusions
Thorough investigation of the geoelectric strike direction beneath the PICASSO Phase I
profile presented in the previous paragraphs results in the following conclusions:
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• Strike characteristics differ between the southern region of the profile associated
with the Betic Cordillera, and the northern region associated with the Tajo Basin.
The Betic Cordillera exhibits complex subsurface structures for the whole depth
range for which no distinct geoelectric strike direction can be identified, whereas
for the Tajo Basin common geoelectric strike directions can be fitted to the majority
of the different depth layers.