Stratification of the Earth beneath the Azores from P and S receiver functions

• Published in: Earth and Planetary Science Letters
• Main Authors: Silveira, G., Vinnik, L., Stutzmann, E., Farra, V., Kiselev, S., Morais, I.
• Other Authors: Instituto Dom Luiz, Campo Grande, Edificio C8, 1749-016 Lisboa, Portugal, Área Científica de Física, Instituto Superior de Engenharia de Lisboa, 1959-007 Lisboa, Portugal, Institute of physics of the Earth, B. Grouzinskaya 10, 123995 Moscow, Russian Federation, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: receiver functions hotspots mantle transition zone Azores; [SDU]Sciences of the Universe [physics]; Ida; North Atlantic
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-02944202; https://doi.org/10.1016/j.epsl.2010.08.021

International audience Seismic recordings of IRIS/IDA/GSN station CMLA and of several temporary stations in the Azores archipelago are processed with P and S receiver function (PRF and SRF) techniques. Contrary to regional seismic tomography these methods provide estimates of the absolute velocities and of the Vp/Vs ratio up to a depth of ~ 300 km. Joint inversion of PRFs and SRFs for a few data sets consistently reveals a division of the subsurface medium into four zones with a distinctly different Vp/Vs ratio: the crust ~ 20 km thick with a ratio of ~ 1.9 in the lower crust, the high-Vs mantle lid with a strongly reduced Vp/Vs velocity ratio relative to the standard 1.8, the low-velocity zone (LVZ) with a velocity ratio of ~ 2.0, and the underlying upper-mantle layer with a standard velocity ratio. Our estimates of crustal thickness greatly exceed previous estimates (~ 10 km). The base of the high-Vs lid (the Gutenberg discontinuity) is at a depth of ~ 80 km. The LVZ with a reduction of S velocity of ~ 15% relative to the standard (IASP91) model is terminated at a depth of ~ 200 km. The average thickness of the mantle transition zone (TZ) is evaluated from the time difference between the S410p and SKS660p, seismic phases that are robustly detected in the S and SKS receiver functions. This thickness is practically similar to the standard IASP91 value of 250 km, and is characteristic of a large region of the North Atlantic outside the Azores plateau. Our data are indicative of a reduction of the S-wave velocity of several percent relative to the standard velocity in a depth interval from 460 to 500 km. This reduction is found in the nearest vicinities of the Azores, in the region sampled by the PRFs, but, as evidenced by SRFs, it is missing at a distance of a few hundred kilometers from the islands. We speculate that this anomaly may correspond to the source of a plume which generated the Azores hotspot. Previously, a low S velocity in this depth range was found with SRF techniques beneath a few other hotspots.