Active fault kinematics and crustal stresses along the Ionian margin of southeastern Sicily

Since the late Cretaceous onset of plate convergence between Africa and Eur ope, the Malta Escarpment has been converted from a Mesozoic passive margin into a mega-hinge fault system with an additional sinistral strike-slip co mponent. The modern tectonic stress regime with NW-SE-directed maximum hori zontal stresses has been established since Late Messinian times. Since the Pleistocene, sinistral strike-slip deformation and contemporaneous normal f aulting along the Malta Escarpment have induced the opening of oblique tren ding onshore grabens at the eastern margin of the Hyblean Plateau. In this study, we focus on the kinematics, the controlling state of stress, and the temporal variation of the neotectonic to active strike-slip and normal fau lt structures. The stress-tenser calculations reveal that the widespread map-scaled to mes o-scaled normal fault structures are governed by the long-term extensional state of stress during the Quaternary. This long-term stress tensor is pred ominantly controlled by gravitational induced stresses due to vertical load (sigma (1) = S-v) and lateral extension due to the topographic gradient of the Malta Escarpment (sigma (3) = S-h = NE-SW). In this case, the average tectonic stresses (sigma (2) = S-H = NW-SE) transmitted by the regional to plate-tectonic stress held are significantly smaller than the gravitational induced stresses. In contrast, the clear localization of conjugate sets of meso-scaled strike -slip fault structures and shear zones without accompanying normal fault st ructures give strong indications for episodic seismotectonic strike-slip fa ulting under critical stress conditions. In this state, tectonically induce d maximum horizontal stresses are successively increased by ongoing plate c onvergence from low-level stress magnitudes (sigma (1) = S-V, sigma (2) = S -H = NW-SE) up to critical stress magnitudes (sigma (1) = S-H = NW-SE, sigm a (2) = S-V), which are significantly larger than gravitational stresses. A t the critical state, seismotectonic stress release occurs by active strike -slip faulting, as recently indicated in mid-crustal levels by the moderate 1990 Augusta earthquake, and re-establishes the long-term extensional stat e of stress. Because the strike-slip faults and shear zones in the study area were forme d as surface ruptures, they additionally give indications of episodic large earthquakes in this region with magnitudes greater than 6.0, as reported b y several large earthquakes devastating E and SE Sicily in historical times . (C) 2000 Elsevier Science B,V. Ail rights reserved.