The 2016 Mihoub (north-central Algeria) earthquake sequence: Seismological and tectonic aspects

Abstract

On 28 May 2016 at 23:54 (UTC), an Mw5.4 earthquake occurred in Mihoub village, Algeria, 60 km southeast of Algiers. This earthquake was the largest event in a sequence recorded from 10 April to 15 July 2016. In addition to the permanent national network, a temporary network was installed in the epicentral region after this shock. Recorded event locations allow us to give a general overview of the sequence and reveal the existence of two main fault segments. The first segment, on which the first event in the sequence was located, is near-vertical and trends E–W. The second fault plane, on which the largest event of the sequence was located, dips to the southeast and strikes NE–SW. A total of 46 well-constrained focal mechanisms were calculated. The events located on the E–W-striking fault segment show mainly right-lateral strike-slip (strike N70°E, dip 77° to the SSE, rake 150°). The events located on the NE–SW-striking segment show mainly reverse faulting (strike N60°E, dip 70° to the SE, rake 130°). We calculated the static stress change caused by the first event (Md4.9) of the sequence; the result shows that the fault plane of the largest event in the sequence (Mw5.4) and most of the aftershocks occurred within an area of increased Coulomb stress. Moreover, using the focal mechanisms calculated in this work, we estimated the orientations of the main axes of the local stress tensor ellipsoid. The results confirm previous findings that the general stress field in this area shows orientations aligned NNW–SSE to NW–SE. The 2016 Mihoub earthquake sequence study thus improves our understanding of seismic hazard in north-central Algeria.