Active Inversion Tectonics from Algiers to Sicily

Abstract

Using an updated active faults map in the easternmost Western Mediterranean (Algeria to Calabria), plus constraints from geodesy (GPS horizontal motion) and seismology (focal mechanisms) input in a strain model, we discussed how the slow Africa-Eurasia motion (4 mm/year) is accommodated along this segment of the Mediterranean. The width of the inverted domains is variable, strain being concentrated into narrow belts in northern Algeria and north Sicily while it is distributed in Tunisia and over the Pelagian platform. The style of deformation further evolves from west to east, from pure thrusting in Algeria to distributed strike-slip in Tunisia to transtension in the Pelagian grabens. We suggest that the present-day deformation is best explained in terms of (1) accommodation of the obliquity following a strain partitioning process with dextral shear onland and en-échelon thrusts offshore northeastern Algeria, along the past trace of the STEP fault that opened the Miocene Algerian Basin, (2) thrusting offshore northern Sicily along the same STEP fault that opened the Tyrrhenian Basin in the Pliocene, (3) increasing thin-skin versus thick-skin in Tunisia as a result of inherited structures, (4) far field Ionian slab pull, strongly active at the Mio-Pliocene initiation of the Pelagian grabens and still remnant today.