The primary role of the Paganica-San Demetrio fault system in the seismic landscape of the Middle Aterno Valley basin (Central Apennines)

Abstract

The Paganica normal fault, that caused the April 9, 2009, L'Aquila earthquake (Central Apennines), is part of the Paganica-San Demetrio fault system (PSDFS). All available data useful to constrain the Quaternary activity of the PSDFS were reviewed, with the aim to point out its role in the landscape evolution of the L'Aquila region and particularly of the Middle Aterno Valley basin. Uplifted remnants of a low relief landscape (Summit Paleosurface, SP) constrain to about 800 m the total offset of the PSDFS since the late Lower Pleistocene. Also, a sedimentary cycle ended at the beginning of Middle Pleistocene is now displaced about 550 m along the PSDFS, whereas alluvial deposits containing tephra layers (560–360 ka) have been displaced more than 150 m by the Paganica fault segment.The long term slip rate values based on this evidence (ranging between 0.4 and 0.9 mm/y), together with the short term slip rate values based on displacements along Late Pleistocene geomorphic features and deposits, have shown that the PSDFS i) has played a primary role in the landscape evolution of the area, despite its minor geomorphic appearance, ii) is linked at depth with other important listric faults located in the PSDFS footwall (Assergi and Campo Imperatore faults) that in this paper are interpreted as secondary faults.This result has relevant seismotectonic implications for the Middle Aterno Valley basin. The PSDFS is the main seismic source of the basin and controls also the seismic potential of other linked structures, including the Assergi and Campo Imperatore faults.