Abstract:
Distinctions between cave morphologies originating from seismic or active tectonics and those generated by natural elastic breakdown or by human activity must be made using unambiguous interpretative criteria. Easily accessible caves in particular, which may have been visited for centuries or millennia, or caves located near engineering works or quarries using great quantities of explosives, may have broken speleothems, breakdowns or detachment joints unrelated to seismic events or tectonic movements. Zambujal cave lies near neotectonic and seismic structures associated with a Plio-Quaternary 200 m uplift of the Arrabida chain and has suffered impacts resulting from quarrying, followed by possible vandalism. It is thus an example for which it is difficult to decipher morphological agents as there is the possibility that identical forms have been generated by several causes, which may have repeated at different episodes of its evolution. However, a careful morphological interpretation makes it possible to accept the existence of two seismic episodes, an 'ancient' one and a 'modern' one. The detection of other episodes between these is only possible using absolute dating. (C) Elsevier, Paris