Active Inversion Tectonics from Algiers to Sicily

International audienceUsing 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

The August 1st, 2014 (Mw 5.3) Moderate Earthquake: Evidence for an Active Thrust Fault in the Bay of Algiers (Algeria)

On August 1st, 2014, a moderate-sized earthquake struck the capital city of Algiers at 05:11:17.6 (GMT+1). The earthquake caused the death of six peoples and injured 420, mainly following a panic movement among the population. Following the main shock, we surveyed the aftershock activity using a portable seismological network (short period), installed from August 2nd, 2014 to August 21st, 2015. In this work, first, we determined the main shock epicenter using the accelerograms recorded by the Algerian accelerograph network (under the coordination of the National Center of Applied Research in Earthquake Engineering–CGS). We calculated the focal mechanism of the main shock, using the inversion of the accelerograph waveforms in displacement that provides a reverse fault with a slight right-lateral component of slip and a compression axis striking NNW–SSE. The obtained scalar seismic moment (M o = 1.25 × 1017 Nm) corresponds to a moment magnitude of M w = 5.3. Second, the analysis of the obtained aftershock swarm, of the survey, suggests an offshore ENE–WSW, trending and NNW dipping, causative active fault in the bay of Algiers, which may likely correspond to an offshore unknown segment of the Sahel active fault