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High-resolution Images of Mantle-wedge Structure along the
Western Hellenic Subduction Zone Using Scattered Teleseismic
Waves
F. D. Pearce (MIT), S. Rondenay (MIT), Maria Sachpazi (National Observatory of Athens), M. Charalampakis (National
Observatory of Athens), A. Hosa (University of Edinburgh), J. Suckale (MIT), L. H. Royden (MIT)
The Hellenic subduction zone is located
in the east-central Mediterranean region
and exhibits large variations in convergence
rate along its western edge [McClusky et al.,
2000]. Differences in the lithosphere entering
the subduction zone are believed to drive the
different rates of convergence. While recent
work has shown evidence for subducted oceanic
crust beneath southern Greece [Suckale
et al., 2009], no detailed images of the mantle-wedge
structure beneath northern Greece
have been available to test this hypothesis.
Here, we use high-resolution seismic images
across northern and southern Greece to
investigate differences in the subducted crust
along the strike of the western Hellenic subduction
zone. We deployed 40 broadband
seismometers from the IRIS Passcal pool
across Greece in a northern line (NL) and
southern line (SL), each roughly perpendicular
to the trench axis as shown in Figure 1a.
We recorded over 50 high-quality teleseismic
events with good azimuthal coverage from
each line and processed them using a 2D
migration algorithm based on the generalized
radon transform. High-resolution images of perturbations in S-wave velocity reveal NE dipping low-velocity layers beneath
both NL and SL as shown in Figure 1b. We interpret the ~10 km thick low-velocity layer beneath SL as subducted oceanic crust
and the ~20 km thick low-velocity layer beneath NL as subducted continental crust. The two imaged subducted crusts connect
smoothly with images from marine seismic surveys [Finetti, 2005] and show a progressive deepening of the oceanic crust of
SL relative to the continental crust of NL (Figure 1c). We conclude that along strike changes in slab buoyancy cause differential
rollback between the two segments, which helps drive the large difference in convergence rates along the western Hellenic subduction
zone.
References
Figure 1: a) Map of study area showing location of southern segment (SS) and northern segment of
western Hellenic subduction zone separated by the Cephalonia transform fault (CTF). White circles
denote station locations for NL and SL deployments. b) Images of perturbation in S-wave velocity for SL
(top) and NL (bottom) at -5% to +%5 (red to blue). Solid lines delineate top and bottom of low-velocity
layer, and the Moho of overriding plate. X-axis is horizontal distance perpendicular to strike measured
from the intersection of SL with the trench of southern segment (solid yellow line in a)). c) Comparison
of subducted crusts imaged from marine seismics (dashed) and this study (solid) for NL (black) and SL
(blue), with dots showing smooth interpolation.
Finetti, I. R. (2005), Depth contour map of the Moho discontinuity in the central Mediterranean region from new CROP seismic data, in
CROP PROJECT: Deep seismic exploration of the central Mediterranean and Italy, edited by I. R. Finetti, pp. 597-606, Elsevier B.V.,
Amsterdam, The Netherlands.
McClusky, S. et al. (2000), Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus,
J. Geophys. Res., 105(B3), 5695-5719.
Suckale J., S. Rondenay, M. Sachpazi, M. Charalampakis, A. Hosa, L. H. Royden (2009) High-resolution seismic imaging of the western
Hellenic subduction zone using teleseismic scattered waves, Geophys. J. Int., 178(2), 775-791.
Acknowledgements: This project was carried out as part of project MEDUSA, funded by the NSF Continental Dynamics Program, grant
EAR-0409373.
II-174 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics