In the Hellenic subduction zone, the lithospheric slab may comprise continental and oceanic units juxtaposed downdip and along strike. For stations along eastern Peloponnesus, teleseismic P-wave receiver-function (RF) processing in the standard frequency band produces an image of a low-velocity layer (LVL) at the top of the slab apparently twice thicker than for an oceanic crust. To assess if this could come from a lack of resolution of the standard processing, we develop a multiscale approach with the RFs based on the wavelet-response of the medium, akin to the wavelet-transform of the velocity-depth function. The synthetic response in conversion is obtained for a multiscale singularity formed by two opposite velocity-steps at the boundaries of a crust embedded in mantle material. This indicates that only wavelet periods shorter than about 0.8 s will allow to identify clearly a 7 km thin oceanic crust. Going to longer periods leads to underestimate or overestimate the time-thickness of the LVL, due to interference phenomena. The analysis of the response in conversion from full waveform synthetic seismograms in a dipping slab model validates a multiresolution approach to real observations. With earthquakes of broad-enough spectrum towards high frequencies, yielding energy to provide wavelet periods significantly shorter than 1 s, the P-to-S conversions obtained allow us to resolve for the first time a standard oceanic crust at the slab top beneath the eastern coast of Peloponnesus. This documents the subduction of a purely oceanic slab of most reduced buoyancy since 4-5 Myr under the rapidly southwestward extending upper plate continental material. © 2010 The Authors Journal compilation © 2010 RAS.
CITATION STYLE
Gesret, A., Laigle, M., Diaz, J., Sachpazi, M., & Hirn, A. (2010). The oceanic nature of the African slab subducted under Peloponnesus: Thin-layer resolution from multiscale analysis of teleseismic P-to-S converted waves. Geophysical Journal International, 183(2), 833–849. https://doi.org/10.1111/j.1365-246X.2010.04738.x
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