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

摘要

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, 6km northwest of the coastal village of Tamentefoust. Waveform modeling of the mainshock resolves a seismic moment M-o=1.73e+17Nm, a moment magnitude M-w 5.5, and a depth of 10.5km. The focal mechanism corresponds to motion on a reverse fault with a left-lateral component striking N252 degrees 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 4km, striking N60 degrees E, dipping toward the NW at 70 degrees for the first 2km of fault depth and 55 degrees 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 (sigma(1)) stress axis oriented N310 degrees 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.