Lithospheric structure in the area of Crete constrained by receiver functions and dispersion analysis of Rayleigh phase velocities

We present a case study of lithospheric structure in the forearc of a retreating subduction zone for the Hellenic Arc. Lateral structural variations along the arc beneath the island of Crete are jointly investigated by receiver functions and Rayleigh phase velocities. Data from temporary short-period networks amend previous results from broad-band stations by broadening the frequency range available for phase-velocity determination and increasing the spatial coverage of receiver function profiles. Both receiver functions and dispersion analysis reveal distinct structural differences between western and central Crete. Western Crete is characterized by nearly constant S-velocities of 3.72-3.75 km s-1 from 10 km depth down to a depth of 50 km and no distinct continental Moho signal. Meanwhile, central Crete shows lower S-velocities equal to 3.3 km s-1 in the crust between 10 and 20 km depth which are followed by the Aegean Moho in about 30 km depth and a mantle wedge with an S-velocity of 4.35 km s-1. Both methods lead to an average depth of 55 km for the subducted oceanic African Moho beneath Crete. This means that the slab is separated from the Aegean crust by a mantle wedge beneath central Crete, while beneath western Crete the corresponding depth region is characterized by crustal velocities. This thickened crust in the forearc might be formed by crustal material of the Aegean Plate dragged down with the subducting African lithosphere. Furthermore, rocks extruded from a melange circulating in a subduction channel might accumulate between a depth of 20 and 50 km and contain low-velocity material, e.g. in the form of serpentinized Aegean mantle. In addition, the lateral extent of a prominent negative phase observed around 4 s differential time in receiver functions from western Crete is mapped. This phase might point to low-velocity material around 30 km depth which could be extruded from a subduction channel. An important property of the forearc found in this study is its strong lateral heterogeneity.