Abstract
This paper presents the results of a large-scale study of surface
wave dispersion performed across Eurasia and North Africa. Improvements
were made to previous surface wave work by enlarging the study region,
increasing path density, improving spatial resolution, and expanding
the period range. This study expands the coverage area northward
and eastward relative to a previous dispersion analysis, which covered
only North Africa and the Middle East. We have significantly increased
the number of seismograms examined and group velocity measurements
made. We have now made good quality dispersion measurements for about
30,000 Rayleigh wave and 20,000 Love wave paths and have incorporated
measurements from several other researchers into the study. We have
improved the inversion from the previous study by adopting a variable
smoothness with the conjugate gradient method for the group velocity
tomography. This technique produces higher-resolution models where
the concentration of data allows it without producing artifacts.
The current results include both Love and Rayleigh wave inversions
across the region for periods from 7 to 100 s on a 1 x 1 deg grid
and at resolutions approaching 1 deg under some conditions. Short-period
group velocities are sensitive to slow velocities associated with
large sedimentary features such as the Caspian Sea, West Siberian
Platform, Mediterranean Sea, Bay of Bengal, Tarim Basin, and Persian
Gulf. Intermediate periods are sensitive to differences in crustal
thickness, such as those between oceanic and continental crust or
along orogenic zones and continental plateaus. At longer periods,
fast velocities are consistently found beneath cratons, while slow
upper mantle velocities occur along rift systems, subduction zones,
and collision zones such as the Tethys Belt. We have compared the
group velocities at various periods with features such as sediment
thickness, topographic height, crustal thickness, proximity to plate
boundaries, lithospheric age, and lithospheric thickness, and we
find significant correlations. We have developed an empirical relationship
between long-period group velocity and lithospheric thickness that
works well for both oceanic and continental lithosphere. We do not
find any similar correlation between the longest-period surface waves
and hot spots.
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