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The Africa-Europe Plate Boundary in Central Italy, Marked by the
Seismic Structure of the Crust and Upper Mantle
Vadim Levin (Rutgers University), Jeffrey Park (Yale University), Nicola Piana Agostinetti (INGV, Italy), Simone
Salimbeni (INGV, Italy), Jaroslava Plomerova (Geophysical Institute, Czech Republic), Lucia Margheritti (INGV, Italy),
Silvia Pondrelli (INGV, Italy)
We examined crustal properties in central Italy using
receiver-function analysis, and probed mantle texture using
observations of splitting in core-refracted shear waves. Our
results reveal profound differences between the “Tyrrhenian”
and the “Adriatic” sides of the convergence zone that is
responsible for the formation of the Apennines.
In the Tyrrhenian domain the crust is apparently thin, and
bound by a relatively sharp impedance contrast at a depth of
approximately 20-25 km. In the Adriatic domain the definition
of the crust–mantle boundary is problematic, suggesting
a gradual and/or complicated transition from the crust to
the mantle. Receiver function analysis is of less help here, as
near-surface structure obscures signals at a number of sites.
Where we can resolve it, the crustal thickness is larger (~35
km). We identify the transition between these two crustal
thickness regimes, and find it to coincide with the high crest
of the Apennines.
The high Apennines also mark the transition in the observations
of shear-wave splitting. We see fairly uniform NW-SE
fast polarizations beneath Tyrrhenian Sea and Tuscany,
while on the Adriatic side we find nearly N-S alignment of
fast polarization, as well as evidence for layering of seismic
anisotropy.
We posit that the high Apennines mark the easternmost
reach of both the “Tyrrhenian” crust and the “Tyrrhenian”
upper mantle, and hence define the eastern edge of the
Eurasian plate in central Italy.
References
Piana Agostinetti, N., V. Levin and J. Park, Crustal structure above
a retreating trench: Receiver function study of the northern
Apennines orogen, Earth Planet. Sci. Lett., 2008.
Salimbeni, S., S. Pondrelli, L. Margheriti, V. Levin, J. Park, J.
Plomerova and V. Babuska, Abrupt change in mantle fabric across
northern Apennines detected using seismic anisotropy, Geophys.
Res. Lett., 34, L07308, 2007
Plomerova, J., L. Margheriti, J. Park, V. Babuska, S. Pondrelli, L.
Vecsey, D. Piccinini, V. Levin, P. Baccheschi, and S. Salimbeni, Seismic anisotropy beneath the Northern Apennines (Italy): Mantle flow or
lithosphere fabric Earth Planet. Sci. Lett.., 247, pp. 157- 170, 2006.
Acknowledgements: Research reported here resulted from the PASSCAL deployment in Italy (http://www.iris.edu/mda/YI?timewindow=2003-2006)
that was a part of the RETREAT project funded by the NSF Continental Dynamics program. Field operations and subsequent work on data
were supported by Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Geophysical Institute of Prague.
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A topographic map illustrates a spatial coincidence of changes in inferred crustal
thickness values (circles with depth-scaled color) and observed fast polarization
directions of split shear waves (black bars). Circle size is proportional to confidence
in the result (largest are most certain). Splitting observations are scaled
with delay and aligned with the fast polarization. Both types of observations
change dramatically across the highest part of the Apennines.
2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics | II-203