Crustal and uppermost mantle structure of Cape Verde from ambient noise tomography
Résumé
We present a seismic ambient noise tomography of the Cape Verde archipelago, located in the Atlantic Ocean, approximately 600 km west of Senegal. We used 38 seismic broadband stations that continuously recorded for 10 months, in order to construct the first 3-D model of Sv-wave velocities for the crust and uppermost mantle beneath the Cape Verde region. We started by computing phase cross-correlations for vertical component recordings using all possible inter-island station pairs. Next, a time-frequency phase-weighted stack was applied to obtain robust Rayleigh wave group velocity dispersion curves in the period band between 10 s and 24 s. Group-velocity maps at different periods are obtained by inverting the dispersion. We then inverted the group-velocity maps to obtain the 3D shear-wave velocity structure of the crust and uppermost mantle beneath Cape Verde. The final 3D model extends from 8 km down to 23 km and has a lateral resolution of about 50 km. The crust in the southwestern sector, encompassing Fogo, presents lower S-wave velocities that may be caused by the presence of melt pockets and/or hydrothermal fluids circulation. The uppermost mantle beneath the northwestern sector is characterized by higher S-wave velocities in agreement with previous results obtained from Ps and Sp receiver functions. Those high-velocity anomalies can reflect non-altered crust or remnants of magma chambers or solidified basaltic intrusions, which fed the volcanism in these islands. Our maps revealed the presence of crustal underplating across the entire archipelago, yet stronger beneath the groups Santo Antão-São Vicente-São Nicolau and Fogo-Santiago-Maio.
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