Assessment of the strong ground motions from the Mw 6.8 earthquake on September 08, 2023 (High Atlas, Morocco)

The 2023 Mw 6.8 earthquake that struct the Al Haouz region in Morroco causes significant ground shaking. This event took place in the western part of the Moroccan High Atlas domain and it had a major effect on the built environment. Many buildings collapsed, roughly, 3,000 people were killed and 6,000 were injured as a result of the earthquake. Unreinforced masonry and adobe buildings in isolated mountain settlements suffered the worst damage. Ground motion parameters such as peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration (SA) are crucial in estimating the seismic performance of structures, assessing the effect of site effects, modeling ground motions for seismic hazard assessments, and update of seismic design regulations. The seismic features of ground movement in Al Haouz were analyzed, identifying factors such as fault rupture, soil conditions, and earthquake source characteristics that influence the strong shaking. One of the three-component acceleration records that was investigated was from a seismic station located near the earthquake epicenter (24 km away), which had a peak (horizontal) ground acceleration of ~0.28 g. We discuss vertical motions recorded from this earthquake as the vertical movement of the ground during earthquakes can also greatly influence the structural integrity of buildings. Finally, preliminary distributions and measures of the average shear wave velocity (Vs30) in the Al Haouz region are discussed, as these values have been used to represent site effects in many ground motion studies and building codes.