Rayleigh wave anelastic attenuation across the Bermuda Rise and the volcanic Caribbean Arch

Abstract

Summary. Average fundamental mode group velocities and attenuation coefficients of Rayleigh waves have been obtained in a region of the Western North Atlantic comprising the Bermuda Rise, the volcanic Caribbean Arch, and normal seafloor greater than 65Myr in age. The average Rayleigh wave attenuation coefficients decrease from a value of 7.78~ 10-4km-' at a period of 15s to a value of 0.21 ~lO-~km-' at a period of 100s. Attenuation values and QR factors obtained are characteristic of a young oceanic region, and they do not correspond to a typical region greater than 65 Myr in age. It is apparent from the data that the high attenuation values reported are due to the effect that the back-arc basin behind the Caribbean Arch has on Rayleigh wave attenuation. Inversion theory applied to the attenuation data yields a Qj' model presenting the same features as those corresponding to extension zones such as the spreading centres of the Atlantic and Pacific Oceans. The low-Q region in the model is situated between depths of around 15 and 100 km, with the maximum Qp' value (- 17 x occurring at about 50 km depth.