Spatial variation of present-day stress field and tectonic regime in Tunisia and surroundings from formal inversion of focal mechanisms: Geodynamic implications for central Mediterranean

Abstract:

We compiled 123 focal mechanisms from various sources for Tunisia and adjacent regions up to
Sicily, to image the current stress field in the Maghrebides chain (from Tunisia to Sicily) and its foreland. Stress
inversion of all the available data provides a first-order stress field with a N150°E horizontal compression
(SHmax) and a transpressional tectonic regime, but the obtained stress tensor poorly fit to the data set.We
separated them into regional subsets (boxes) in function of their geographical proximity, kinematic
regime, homogeneity of kinematic orientations, and tectonic setting. Their respective inversion evidences
second- and third-order spatial variations in tectonic regime and horizontal stress directions. The stress
field gradually changes from compression in the Maghrebides thrust belt to transpression and strike slip
in the Atlassic and Pelagian foreland, respectively, where preexisting NW-SE to E-W deep faults system
are reactivated. This spatial variation of the sismotectonic stress field and tectonic regime is consistent
with the neotectonic stress field determined by others from fault slip data. The major Slab Transfer Edge
Propagator faults (i.e., North-South Axis-Hammamet relay and Malte Escarpment), which laterally delimit
the subducting slabs, play an active role in second- and third-order lateral variations of the tectonic
regime and stress field orientations over the Tunisian/Sicilian domain. The past and current tectonic
deformations and kinematics of the central Mediterranean are subordinately guided by the plate
convergence (i.e., Africa-Eurasia), controlled or influenced by lateral slab migration/segmentation and
by deep dynamics such as lithosphere-mantle interaction.