Revisiting the Laalam (Eastern Algeria) March 20, 2006 (Mw 5.1) Earthquake and its Seismotectonic Implication

Hypocenters of main shock and aftershocks of the March 20, 2006 Laalam earthquake are relocated using HypoDD double-difference technique. We combined accelerogram and seismogram data of the National Center of Applied Research in Earthquake Engineering (CGS). Among about 191 aftershocks, recorded at least by 4 stations, 141 aftershocks of M d 1.2–2.7 were relocated using HypoDD. The obtained swarm of epicenters occupying a crustal volume of 5 km × 3 km × 5 km and the focal mechanism corresponds to an unknown pure left lateral strike slip, trending N174°E. We were able to calculate focal mechanisms for only seven aftershocks with more than seven polarity readings, which give a P axis oriented NNW–SSE. The waveform inversion also provided values of M w 5.1, M 0 5.9 10 −16 Nm and the depth 4.9 km. The dislocation and the stress drop were estimated to 90 cm and 16.5 bars, respectively.