The Irpinia region is one of the most seismically active areas of Italy due to ongoing, late-orogenic extension in the axial zone of the Apennines mountain belt. However, the 3D architecture and the nature of the faults that drive this extension are still uncertain, posing challenges to seismic hazard assessment. Here, we address these uncertainties by integrating a new catalog of high-resolution micro-seismicity (ML<3.5) complemented by earthquake focal mechanisms, with existing 3D seismic velocity models and geological data. We found that micro-seismicity is primarily taking place along a segmented, approximately 60 km long, deep-seated, Mesozoic normal fault that was inverted during the shortening stages of the Apennine orogeny and then extensionally reactivated during the Quaternary. These findings suggest that multiple events of reactivation of long-lived faults can weaken their strength, making them prone to co-seismic remobilization under newly-imposed strain fields in active mountain belts.

This study is based on a large 3D seismic dataset in the deep-water domain in the Niger Delta. The study area is characterized by a series of WNW-ESE trending anticlines cored by shales. They developed by shortening at the toe of the gravity system since Miocene times. Four units of syn-kinematic sediments, reaching a maximum thickness of ~ 800 m, accumulated in the tectonically subsiding synclines during fold amplification between ~ 9.5 Ma and ~ 1.8 Ma. The volumes of syn-kinematic units roughly balance those of the shales accumulated in thickened fold cores. This feature is consistent with folding resulting from buckling controlled by the competence contrast between isopach Cenozoic units and underlying overpressured shales of the Akata Formation. This interpretation rules out the occurrence multiple thrust flats, the maximum cumulative shortening associated with folds and related thrust ramps being of ~ 3.5 km. A dense network of NE-SW striking oblique extensional faults offsets a prominent anticline characterized by a NE-SW trend (which is almost perpendicular to the regional fold trend). These faults form a narrow, continuous deformation zone extending for tens of kilometers along and beyond the length of the anticline. The faults, rooting within the shales of the Akata Formation, formed since ~ 5 Ma and deform the seabed. Displacement distribution suggests mechanical interaction between isolated fault segments within the deformation zone. The latter is interpreted as the shallow expression of a deep-seated fault zone inherited from the segmented passive margin and marked by gravity and magnetic data.

2-D finite element modeling of both coseismic and interseismic deformation was performed along a transect across the seismogenic fault of the Mw=7.3, November 2017 Lurestan earthquake (Zagros Mountains). In order to extract information on the time-space distribution of uplift along the same transect, an investigation of the large-scale features of topography and river network was also carried out. Constraints from the spatial distribution of mean elevation, local relief and normalized channel steepness index (ksn), combined with those from river longitudinal profiles and transformed river profiles (chi-plots), were integrated with the results of geomorphological analyses aimed at the reconstruction of the development of the fluvial network. Despite the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphological signature. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. They point out how co-seismic slip controls localized uplift of a prominent topographic feature ­– defining the Mountain Front Flexure – located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located further to the NE, in the interior of the orogen.

The Zagros thrust belt formed due to the convergence between the Arabian and Eurasian plates during the closure of the Neo-Tethys Ocean. GPS measurements show that the northward relative motion of the Arabian Plate is still active today. This active drift produces high-magnitude earthquakes along the Zagros thrust belt, such as the Iran-Iraq border seismic event of November 12, 2017 (Mw = 7.3), nucleated along the “Mountain Front Fault”. The aim of this work is to study the inter-seismic and co-seismic deformation that eventually leads to the nucleation of important seismic events in the study area. A 2-D finite element model has been performed starting from published geological sections and relevant seismological datasets, integrated with geo-mechanical parameters of the rocks. The results of finite element modeling (FEM), including predicted uplift pattern and rate along the analysed crustal section, are compared with a tectonic geomorphology analysis in order to unravel the most reliable tectonic scenario for the active tectonic setting of the study area.