Crustal Attenuation Tomographic Image of Northern Morocco: Indication of High Tectonic Activities

Abstract

Northern Morocco is known by its complex tectonic activity and has been the subject of various geophysical and geodynamic studies aimed to understand the physical properties and composition of the Earth’s crust and upper mantle. The waveforms of earthquakes recorded by the Topo – Iberia – Picasso seismic networks from 2008 to 2012 are analyzed to determine the decay properties of the coda wave and map the attenuation and absorption properties of the crust in this region. The coda quality factor Qc was estimated in five non‑overlapping frequency windows, ranging from 1.5 to 24 Hz, using recordings of local earthquakes. The measurements of Qc were then used to create maps of the absorption quality factor (Qi) using a linearized approximation. These maps were compared with the tectonic settings of the region to gain further insight into the crustal properties. Lateral and vertical variations of the coda quality factor (Qc) were investigated by creating a three‑dimensional tomographic image of the region. The results showed strong lateral variations of absorption in the northern part of Morocco, indicating high tectonic activity. Areas with high tectonic activity and high absorption were characterized by low values of Qc, while areas with low tectonic activity and low absorption had high values of Qc. The areas with thick cover sedimentary materials and shallow geothermal activity showed low‑frequency absorption. When compared to previous studies in northern Morocco, the study provides new information about the three‑dimensional attenuation model of the Earth’s crust.