Active faulting, 3-D geological architecture and Plio-Quaternary structural evolution of extensional basins in the central Apennine chain, Italy

The general “basin and range” Apennine topographic
characteristic is generally attributed to the presently
active normal fault systems, whose long-term activity
(throughout the Quaternary) is supposed to have been responsible
for the creation of morphological/structural highs
and lows. By coupling field geological survey and geophysical
investigations, we reconstructed the 3-D geological
model of an inner tectonic basin of the central Apennines, the
Subequana Valley, bounded to the northeast by the southern
segment of one of the major active and seismogenic normal
faults of the Apennines, known as the Middle Aterno Valley–
Subequana Valley fault system. Our analyses revealed that,
since the late Pliocene, the basin evolved in a double halfgraben
configuration through a polyphase tectonic development.
An early phase, Late Pliocene–Early Pleistocene in
age, was controlled by the ENE–WSW-striking and SSEdipping
Avezzano–Bussi fault, that determined the formation
of an early depocentre towards the N–NW. Subsequently, the
main fault became the NW–SE-striking faults, which drove
the formation during the Quaternary of a new fault-related
depocentre towards the NE. By considering the available
geological information, a similar structural evolution has
likely involved three close tectonic basins aligned along the
Avezzano–Bussi fault, namely the Fucino Basin, the Subequana
Valley, and the Sulmona Basin, and it has been probably
experienced by other tectonic basins of the chain. The
present work therefore points out the role of pre-existing
transverse tectonic structures, inherited by previous tectonic
phases, in accommodating the ongoing tectonic deformation
and, consequently, in influencing the structural characteristics
of the major active normal faults. This has implications
in terms of earthquake fault rupture propagation and segmentation.
Lastly, the morpho-tectonic setting of the Apennine
chain results from the superposition of deformation events
whose geological legacy must be considered in a wider evolutionary
perspective. Our results testify that a large-scale
“basin and range” geomorphological feature – often adopted
for morpho-tectonic and kinematic evaluations in active extensional
contexts, as in the Apennines – just led by rangebounding
active normal faults may be actually simplistic, as
it could not be applied everywhere, owing to peculiar complexities
of the local tectonic histories.