Evidence of Seismic Gap in Al Hoceima (Morocco): Implication for Seismic Hazard

This paper uses high-resolution seismic profiles of the complex active zone of Al Hoceima (Morocco) to illuminate the active fault system, acquired along a main, 10 km long transect cutting across the strands of an active fault system in Al Hoceima bay area. The investigation approached was to tackle and follow faults vertical offset. The final seismic sections led to identify faults on the profiles and to distinguish the likely-active ones, with visible wide deformation features, where normal strike-slip faults trend N–S and NW–SE, principally related to the major Al Idrissi strike-slip fault system. To aid interpretation of this complex setting, we complemented seismic images with seismicity catalogs and focal mechanism solutions to investigate the active tectonics. These faults are accommodating an important part of the complex seismotectonic movements. Seismicity catalog in the Al Hoceima area exhibits a moderate seismic release (Mw < 6), with shallow depths mostly ≤ 20 km, focal mechanisms suggest mainly a strike-slip regime with a subvertical σ3 and subhorizontal σ1 implying a transtensional regime in the area. The seismicity seems to be confined between two major faults: Trougout in the east and Rouadi in the west. However, this trend is no longer respected in the last 2 years as seismic activity is shifting toward the eastern side of the Trougout fault. Moreover, a seismic gap zone around this fault is evident considering the instrumental seismicity catalog of last 100 years. This fault system and related seismicity could represent a potential hazard for neighbor cities.