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Abstract:
New combined P receiver functions and seismicity
data obtained from the EGELADOS network employing
65 seismological stations within the Aegean constrained
new information on the geometry of the Hellenic subduction
zone. The dense network and large data set enabled us to estimate
the Moho depth of the continental Aegean plate across
the whole area. Presence of a negative contrast at the Moho
boundary indicating the serpentinized mantle wedge above
the subducting African plate was seen along the entire forearc.
Furthermore, low seismicity was observed within the serpentinized
mantle wedge. We found a relatively thick continental
crust (30–43 km) with a maximum thickness of about
48 km beneath the Peloponnese Peninsula, whereas a thinner
crust of about 27–30 km was observed beneath western
Turkey. The crust of the overriding plate is thinning beneath
the southern and central Aegean and reaches 23–27 km. Unusual
low Vp = Vs ratios were estimated beneath the central
Aegean, which most likely represent indications on the pronounced
felsic character of the extended continental Aegean
crust. Moreover, P receiver functions imaged the subducted
African Moho as a strong converted phase down to a depth
of about 100 km. However, the converted Moho phase appears
to be weak for the deeper parts of the African plate
suggesting nearly complete phase transitions of crustal material
into denser phases. We show the subducting African
crust along eight profiles covering the whole southern and
central Aegean. Seismicity of the western Hellenic subduction
zone was taken from the relocated EHB-ISC catalogue,
whereas for the eastern Hellenic subduction zone, we used
the catalogues of manually picked hypocentre locations of
temporary networks within the Aegean. Accurate hypocentre
locations reveal a significant change in the dip angle of
the Wadati–Benioff zone (WBZ) from west (25) to the
eastern part (35) of the Hellenic subduction zone. Furthermore,
a zone of high deformation can be characterized
by a vertical offset of about 40 km of the WBZ beneath the
eastern Cretan Sea. This deformation zone may separate a
shallower N-ward dipping slab in the west from a steeper
NW-ward dipping slab in the east. In contrast to hypocentre
locations, we found very weak evidence for the presence
of the slab at larger depths in the P receiver functions, which
may result from the strong appearance of the Moho multiples
as well as eclogitization of the oceanic crust. The presence of
the top of a strong low-velocity zone at about 60 km depth in
the central Aegean may be related to the asthenosphere below
the Aegean continental lithosphere and above the subducting
slab. Thus, the Aegean mantle lithosphere seems to
be 30–40 km thick, which means that its thickness increased
again since the removal of the mantle lithosphere about 15 to
35 Ma ago.
