P. Schmoldt, PhD - MTNet - DIAS

7. Geology of the Iberian Peninsula
Depth (km)
AK135
(continental structure model)
P-wave velocity (km/s)
36ON M.S.
b
PICASSO Phase I profile
Betic C. CIZ Tajo Basin
c
a
e
dP-wave velocity
d
41 O N
100
300
500
Depth (km)
41 O 0.082’N
-2 O 38.760’W
36 O 0.249’N
-2 O 58.262’W
Fig. 7.24.: Anomalies of P-wave velocity in respect to the AK135 reference model (left hand side) [Kennett et al., 1995] for a transect
coinciding with the PICASSO Phase I profile, extracted from a global travel time tomography model [Amaru, 2007]; Betic C.: Betic
Cordillera, CIZ: Central Iberian Zones, M.S.: Mediterranean Sea; see text for details.
P-wave travel time variation relative to the AK135 reference model [Kennett et al., 1995]
(Fig. 7.24). Synthetic tests show that anomalies up to 0.5 × 0.5 degree in the original
3D model can be reconstructed in the best-sampled regions of the uppermost mantle for
the European–Mediterranean region, with resolution decreasing with depth. Based on
results of spike-tests and hit count map inspection, most features of the vertical transect
are found to be reliable [Amaru 2010, pers. communication], with the region of least
sensitivity (less than 500 rays/cell) located in the northern extend of the crust beneath
the Tajo Basin. The cell size increasing with depth, from 10 km in the crust to 50 km at
a depth of 660 km, implies a corresponding sensitivity decrease with depth. Moreover,
the vertical extend of features at greater depth is accordingly less constraint than those of
crustal structures.
Key elements of the model are: (a) relatively high velocity of the crust; (b) the low
velocity lithosphere beneath Betic Cordillera and Mediterranean Sea; (c) the high velocity
region at sublithospheric depth beneath the Betic Cordillera; (d) the vertical change
of velocity beneath the northern Tajo Basin; as well as (e) the low velocity zone beneath
the Tajo Basin, observed at mantle depth with a northward dip and a small branch reaching
north- and upwards in the lithospheric-mantle. No interpretation for features of this
particular transect are published by the authors at this stage, meaning that all conclusions
presented here provide new insights about processes taking place in the Iberian Peninsula.
Therefore, these features are examined here in more detail, together with a brief
interpretation of possible mechanisms.
(a) The relatively fast crust is most likely due to an inaccurate representation of the local
conditions by the AK135 model used as reference during the study. (b) The relatively low
velocity region beneath Betic Cordillera and Alboran Sea, at depth between 30 km and
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