Constraining the crustal root geometry beneath Northern Morocco

What is it about?

Consistent constraints of an over-thickened crust beneath the Rif Cordillera (N. Morocco) are inferred from anal-yses of recently acquired seismic datasets including controlled source wide-angle reflections and receiver func-tions from teleseismic events. Offline arrivals of Moho-reflected phases recorded in RIFSIS project provide estimations of the crustal thicknesses in 3D. Additional constraints on the onshore–offshore transition are in-ferred from shots in a coeval experiment in the Alboran Sea recorded at land stations in northern Morocco. A re-gional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain receiv-er functions and explore the crustal thickness variations with a H-κ grid-search approach. This larger dataset pro-vides better resolution constraints and reveals a number of abrupt crustal changes. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely indepen-dent data and methods. Both approaches document a large crustal root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favors models proposing that the high velocity slab imaged by seismic to-mography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area beneath western Alboran Sea and the super-ficial seismicity in Alhoceima area. Therefore, the presence of a crustal root seems to play also a major role in the seismicity distribution in northern Morocco.

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