Comparing cumulative displacements at various time scales: insights into complex segment linkage along an active extensional system

Major normal fault systems are composed of segments that link as displacement accumulates, with linkage zone characteristics that reveal fault zone evolution. The steeply southwest-dipping Aremogna Fault (ACF) and Cinque Miglia Fault (CMF) in the southeastern Abruzzo region (Central Apennines - Italy), are connected by a complex relay zone that developed between the two subparallel NW-striking segments, 2-4 km away from the main villages. The overall normal fault system is 16 km long and range bounding, with adjacent intermontane basins: the Aremogna plain at an average elevation of 1450-1500 m a.s.l. to the south, and the Cinque Miglia one (1250 m a.s.l.) to the north filled by glacial- fluvioglacial and alluvial-lacustrine deposits, respectively. Geologic map data derived from a field survey and nine cross-sections reveal synthetic and antithetic Quaternary normal active segments, showing a range of geometries including along strike-changes and step-overs. First results from displacement profiles suggest that deformation at the relay zone between ACF and CMF was initially dominated by two overlapping subparallel faults that became linked toward the south. With a complex fault network, the present-day setting shows offsets that transition smoothly from the lower displacement (~500 m) southern segment to the higher displacement (~1000 m) northern segment. The cumulative offset is also assessed on each fault portion towards the north exhibiting morphological evidence of activity by topographic profiles extracted from a high-resolution DEM and then compared with geological throws. That transition, combined with extensional deformation within the zone, suggests that connected Aremogna-Cinque Miglia Fault System (ACMFS) could be associated with future major ruptures as identified in paleoseismological studies (D’Addezio et al., 2001). The model of fault evolution presented here has implications also for those investigating seismic hazards.