Strain partitioning and fault interaction during the 2023 Mw 6.8 Al-Haouz earthquake, Western High Atlas, Morocco

Abstract

This study employs a multidisciplinary approach to identify the seismogenic fault responsible for the Mw 6.8 Al Haouz earthquake of September 8, 2023, in the Western High Atlas, Morocco. In addition, considering the oblique slip dynamics and strain partitioning characteristic of the region, the study investigates potential interactions between fault systems at depth. Our new relocation of the mainshock confirms the depth of the mainshock at ca. 28 km, while our relocated aftershocks reveal clusters concentrated near the Tizi n’Test fault (TnTf) and aligned patterns consistent with fault-controlled seismicity. Focal mechanisms of the mainshock indicate a compressive event involving two nodal planes: a high-angle NW-dipping plane and a low-angle SW-dipping plane. DInSAR analysis generated displacement maps for vertical and horizontal (E-W) components, revealing an asymmetric SW-verging uplift bounded, in the south, by the NW-dipping Tizi n’Test fault (TnTf). The Triangular Elastic Dislocation (TDE) method is conducted to simulate complex faults geometries using geological data and focal mechanism solution.

The NW-dipping TnTf shows a better fit with the observed deformation compared to the SW-dipping Jebilet Thrust (JTt), which contributed with a minor role. Coulomb stress changes calculated from the TDE model correlates with aftershocks distribution, further supporting the TnTf as the causative fault, with a partial influence of the JTt.

Our findings emphasize the value of integrating geodetic observations with advanced modelling to enhance the understanding of the seismotectonic framework, offering a refined reconstruction of the Western High Atlas's deformation processes during the 2023 Al Haouz earthquake.