The March 2017 earthquake sequence along the E-W-trending Mcid Aicha-Debbagh Fault, northeast Algeria

In Northeast Algeria, a sequence of 143 small earthquakes (M-d <= 4.7) occurred near the Mcid Aicha-Debbagh (MAD) Fault between 4 and 16 March, 2017. During this sequence, 74% of the seismic activity occurred in the first two days. Although the earthquakes were not large, they yielded important new information and have improved our understanding of seismic activity in three distinct regions along the fault. In the Sidi Dris region (western MAD Fault), 106 events (1 <= M-d <= 3.2) were located in an aftershock cluster trending NNE-SSW, highlighting a transverse fault with similar to 6 km of strike-slip displacement that locally cuts the MAD Fault. In the El Kantour region (central MAD Fault), 31 events were recorded along a 3 km long fault segment, including the M-w 4.7 mainshock. The mainshock had a focal mechanism consistent with predominantly strike-slip motion on a N110 degrees E-striking fault plane, in agreement with the WNW-ESE orientation of the central MAD Fault segment. Finally, six diffuse events occurred in the Hammam Debbagh region (eastern MAD Fault). A significant event (M-d 3.0) in this region had a focal mechanism consistent with strike-slip movement and a normal component trending NW-SE. This is consistent with the fault plane orientations of key events in the time period 2003-2014, likely related to the NW-SE-striking Hammam Debbagh Fault. The present-day stress tensor is characterized by a strike-slip tectonic regime and a sigma(1) orientation (N342 degrees E) that closely matches the maximum regional compressive stress orientation (NNW-SSE).

Automated summary

A series of 143 small earthquakes near the MAD Fault in Northeast Algeria occurred between March 4 and 16, 2017, providing important new information on seismic activity in different regions along the fault. The seismic activities in Sidi Dris, El Kantour, and Hammam Debbagh regions show distinct characteristics, reflecting different tectonic features. This study reveals a strike-slip tectonic regime and provides insights into the stress tensor orientations in the region.