Seismic site effects and aptitude to urbanization for the study area of Taroudant, South-West of Morocco

An integrated study combining ambient noise data analysis and Multichannel Analysis of Surface Waves (MASW) 1-D shear wave velocity profiles was conducted for earthquake mitigation in the study area of Taroudant, South-West of Morocco. To assess soil site effects and the physical characteristics of the near-surface layers, microtremor measurements were taken at 72 sites to obtain H/V ratios, and 17 MASW profiles were recorded. Two classes of dominant frequencies were identified. The low frequencies of class 1 are attributed to the top of a Paleozoic rigid basement located at a depth of at least 75 m, while the high frequencies of class 2 are likely generated by near-surface seismic interfaces at depths ranging from 6 to 10 m. A thick Plio-Quaternary alluvial sedimentary cover, composed mainly of poorly consolidated clays and silts to consolidated conglomerates, has accumulated in either flat-lying layers or in small depressions with limited extent.

Maps constructed from the 1-D 1D Vs-depth profiles indicate that the rocks underlying the study area have significant rigidity, as evidenced by the Vs30 values, which range between 360 and 750 m/s. The computed Vs30 values place the soil in the S2 class according to the classification of soils in the Moroccan seismic design code (RPS 2000, Version 2011). The calculated amplification factors range from 1.68 to 2, with higher values observed in the southwestern part of the area, where the near-surface geology consists primarily of soft silty terraces and alluvium deposited by the Oued Souss River. Lower amplification values are found in the northern part of the area, where the sediments are primarily composed of relatively consolidated to semi-consolidated alluvial deposits. Overall, the study area is characterized by low to moderate amplification factor values (1.68 to 1.88), indicating that the area may experience low to moderate seismic site effects in the event of a significant earthquake.