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others. Even having gone forward in the information collected about such complex
tectonic situation, we need more elements to clarify the models given.
In any case, the following aspects seem already irrefutable:
-
The earthquake was originated in a collision area between plates, that approach
each other at a low rate (5 mm/year).
-
Areas of more crustal compression in the Iberian Peninsula and its surroundings
are already known (Fig. 7).
-
With the present information on the relative shallow depth of focal locations, the
fault rupture associated to the earthquake (Mw
8.7) must extend several hundred
kilometres. So, the various geological structures already identified are too small,
even if they rupture in “cascade” by sympathy, to explain the amount of energy
released, unless the source is deeper than presently thought or of sub-horizontal
nature as Terrinha
et al.
(2003) propose. In this case, an horizontal zone involving
all structural systems of Fig. 6(a) between 9
◦
>
30
-10
◦
W and 36
◦
-38
◦
N, would
rupture.
-
The mechanism is different from the 1969 earthquake.
-
The recent seismicity and even the one from the final of the XXth century, much
more rigorous in the localization of the epicentres and in the definition of the
source mechanisms, they do not define clearly a pattern of activity allowing
a good acknowledgement of the geo-dynamic at SW of the Iberian Peninsula
Fig. 7
Contact between the two Euro-Asian and African Plates and the main geological structures
(Cabral, 1993) - the arrow indicates the predominant movement of the African Plate in relation to
the Euro-Asiatic Plate
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