TETTONICA ATTIVA IN APPENNINO CENTRALE E IMPLICAZIONI PER L'ANALISI DELLA PERICOLOSITÀ SISMICA DEL SETTORE ASSIALE DELLA CATENA UMBRO-MARCHIGIANA-ABRUZZESE

Abstract

In peninsular Italy the Centrai Apennines Fault System (CAFS), overprinting earlier structures of a Neogene thrust belt, includes segments characterized by a diffuse seismicity distributed within a 50-60 km wide zone. The system has been analysed by means of morphotectonic and structural inves­tigations of exposed active fault segments. The CAFS pat­tern and its overall kinematics have been related to left-lateral strike-slip motion on north-south trending crustal faults. Post­Wurmian vertical vs. horizontal slip rate ratios computed from linked outcropping CAFS structures, display a consis­tent value of ca 1:3. The remote stress field responsible for the development and evolution of the CAFS, as inferred from slip vector analysis and seismological and paleomagnetic data, is characterized by a NW-SE compression and by a NE-SW extension. The existence of deep-seated strike-slip faults in the centrai Apennines has implications for seismic hazard analysis. Motion along these structures implies, in fact, that coseismic surface faulting is distributed, and that cumulative displacements include normai and strike-slip components. This suggests that single-segment rupture models must be used with caution in seismic hazard analysis and that segmenta­tion criteria should include other factors playing a role in par­titioning the deformation within volumes or areas. Examples of areal segmentation within the CAFS show that the seis­mogenic potential of a major fault structure is best described by multiple-ruptures models and better analysed in terms of partial contributions of lower-rank features constituting con­gruent structural associations within the system.