Geological evidence of recent fault evolution. Examples from Campo Imperatore (L'Aquila - central Apennines)

Abstract

Two recent brittle tectonics manifestations recognised in the Campo Imperatore basin, L'Aquila (Italy), are reported and analysed. Both are characterised by a series of morphological features common to many similar manifestations in both the Apennines and the Alps. The Mandrucce fault system has produced a continuous series of secondary badland-type hydrographic basins on the NE slope of Campo Imperatore. These basins are located in the relatively uplifted sector and are sharply restricted at the intersection with the faults; here they give rise to a sequence of triangular or trapezoidal facets. The Cocchiare fault, on the other hand, transversely cuts the terraced fan of the Rio della Fornaca. The scarp representing the morphological expression of this fault distinctly separates the succession of stream-borne deposits of the uphill sector from that of the equally terraced downhill sector. The latter, however, is characterized by the different thickness of the individual sedimentary bodies and a different altimetric distribution of its basal support surfaces, which cannot be geometrically correlated with those of the uphill terraced sector. Both manifestations, however, display geological features that make it certain that these morphological features are linked to the presence of faults that have undergone evolution very recently (Upper Holocene). In the Mandrucce system, in fact, have been recognized fault planes that displace, often in a polyphasic manner, very recent deposits (stratified debris chronologically correlatale with the area's most recent glacial deposits, and sheet erosion products younger than the last local glacial advances).These faults display slightly different typologies that are interpreted as manifestations of a single, brittle deformation phase that took place at progressively lower depths. The most surficial and most recent manifestations are thus overprinted on the progressively exposed, deeper and older manifestations. The morphology of the Cocchiare fault is attributable solely to dynamic interaction between the relatively rapid evolution of the structure, as observed in an excavation, and the very rapid fluvial sedimentation and erosion episodes on the part of the Rio della Fornaca. The results of this analysis suggest that it would be advisable to review some of the many manifestations of recent tectonic activity described in the literature on the strength of morphological features alone to see whether they are really supported by significant geological data.