Actividad neotectónica de la Falla de Alentejo-Plasencia en Extremadura (Macizo Hespérico).

Résumé

Signs of recent tectonic activity are found at the Extremadura sector of Alentejo-Plasencia fault. This fault was active during the alpine compressional period as a sinistral strike-slip fault at the foreland of a collisional zone and presents sorne activity from the Miocene to the Quaternary. Upper «Raña» deposits of Early Villafranquian age, present an around-2-meter-vertical-displacement at the north border of Alburquerque granitic massif. Clase to this point old fluvial terraces of unknown age are folded and faulted, and low terraces (3 m above present river course) are jointed. In the tertiary Cañaveral pull-apart basin, at the Alcantara reservoir border, the fault disrupts a Tagus river fluvial terrace, which lies 80 m above the river course and has a probable Middle Pleistocene age. All these observations imply a vertical displacement which could be related to a slip rate less than 0.001 mm/year. lf this fault is compared with other active faults of the Hesperian Massif, such as the Bragança-Manteigas one, it becomes clear that Alentejo-Plasencia fault is less active. There are though paleoseismicity structures associated to the Alentejo-Plasencia fault, such as liquefaction features.