The 13 July 2019 Mw 5.0 Jijel Earthquake, northern Algeria: An indicator of active deformation along the eastern Algerian margin

摘要

On July 13, 2019, a moderate earthquake shook the Jijel region of Algeria, similar to 300 km east of Algiers (Capital of Algeria). In the past, the Jijel region experienced a destructive earthquake (I-0: X) on 21-22 August 1856, triggering a moderate tsunami in the western Mediterranean region. The 2019 event is the second important event to have occurred along this part of the Algerian margin, which has been undergoing an inversion process since the Pliocene Epoch. The event occurred 40 km to the north of Jijel City, at 10 km depth. No property damage or injuries were associated with this event. The seismic moment release estimated from waveform modeling was M-0 = 3 x 10(16) Nm, corresponding to a Mw 5.0 event. The mainshock focal mechanism is associated with the rupture of an E-W thrust fault that is clarified by a 4-km-long x 10-km-wide aftershock cluster along the continental slope of the Jijel margin. In the same area, similar to 30 km to the west and offshore of the coastal village of Ziama-Mansouriah (west of Jijel) a Mw 4.1 earthquake occurred in 2014. This event is also associated with the rupture of a western contiguous E-W thrust fault. Stress tensor inversion produces a main (sigma(1)) maximum stress axis oriented N356E, which is in agreement with previous stress studies of the Lesser Kabylia-Babors block. The present-day stress field is characterized by a compressional tectonic regime (R' = 2.96 +/- 0.21). Coulomb stress analysis of the 2014 Ziama and 2019 Jijel earthquakes indicates that the two earthquakes appear to be individually triggered events with no stress transfer between them. The 2019 Jijel earthquake is associated with one of the three active en echelon faults that have already been identified in the central part of the Algerian margin via recent marine surveys. It belongs to the serie of many moderate seismic events that have recently affected the Algerian margin (Boumerdes, Algiers, Bejaia), and is representative of the active deformation process along the Algerian margin that is marked by the initiation of an incipient subduction zone with a progressive plate boundary migration since the late Miocene.