The Algiers (north central Algeria) earthquake of August 1st, 2014 Mw 5.5 in the Algiers Bay tectonic context

Abstract

On 1 August 2014, shaking from a moderate earthquake affected Algiers, the capital of Algeria. The event was located by the CRAAG seismic network in the eastern part of Algiers Bay, 6 km northwest of the coastal village of Tamentefoust. Waveform modeling of the mainshock resolves a seismic moment Mo = 1.73e+17 Nm, a moment magnitude Mw 5.5, and a depth of 10.5 km. The focal mechanism corresponds to motion on a reverse fault with a left-lateral component striking N252°E. By analyzing 576 aftershocks recorded in the first month after the mainshock, we demonstrate that the earthquake was caused by a curved NE–SW-striking reverse fault with a length of 4 km, striking N60°E, dipping toward the NW at 70° for the first 2 km of fault depth and 55° at greater depths. A minor strike-slip fault aligned roughly N–S crosscuts the eastern part of the reverse fault. The stress tensor inversion produces a main compressional (σ1) stress axis oriented N310°E, in agreement with the NW–SE compression in the central part of northern Algeria. This newly recognized offshore fault system along the Algiers margin illustrates the complexity of the tectonic domain in Algiers Bay, where several active faults meet, including the Thenia Fault, a NE–SW-striking flanking fault that marks the southern border of the Algiers metamorphic massif, and the western part of the Boumerdes Fault.