Active deformation in Algeria from continuous GPS measurements

The present-day kinematics of plate boundary deformation in the western Mediterranean is now well described by space geodetic measurements, except for the Algeria-Tunisia part of north Africa where information is still lacking. Yet, that portion of the Nubia-Eurasia Plate boundary likely concentrates most of the oblique plate convergence, with an on-going debate on the role of offshore versus on-land active-and seismogenic-structures. Here we use 10 yr of continuous GPS data from the Algerian REGAT network to compute the first geodetic velocity field in Algeria. In the west, velocities are uniform and collinear to the plate convergence trend, with a sharp gradient at the coast, while in the east they indicate that deformation involves a broader region. Using a simple block kinematic approach, we show that the velocities are consistent with the presence of an active, reverse, offshore fault system that runs along the toe of the Algerian margin, with a slip rate decreasing from west to east. In the western half of Algeria, the GPS data do not require additional faults system on-land. In the eastern half, GPS velocities require an E-W-trending strike-slip fault separating two blocks that accounts for the strike-slip component of the overall plate motion. We also observe significant shortening between the Saharan platform and the Aures range in southeastern Algeria. This first-order description of the Eurasia-Nubia oblique convergence in Algeria provides new guidelines for seismic hazard assessment but still requires denser geodetic measurements over this vast territory.