Active strain-rate Across the Messina Straits and Kinematics of Sicily and Calabria From GPS Data

vienna, austria.

The Messina Straits is the locus of one of the strongest seismic event that ever hit Italy during historical times,
the 1908 Mw 7.1 earthquake, and the same region also suffered major damage from other strong earthquakes
in the last few centuries. However, despite the large amount of data and studies carried out, our knowledge of
the present-day deformation of this area is still debated. While a general consensus has been reached about the
kinematics of the 1908 causative fault, less is known about the rate and shape of interseismic loading across the
Straits, and debate continues also about the general kinematics and geodynamic framework of this region which
are strongly influenced by subduction and retreat of Ionian lithosphere. Thanks to the increasing number of GPS
Networks in the study region it is now possible to study both the regional kinematics and strain loading across
active faults. In this work we analyze all the observations collected over the Messina non-permanent GPS Network
for the 1994-2008 time span, and data from about 600 CGPS stations in the Euro-Mediterranean region, using the
GAMIT software.
The output of our analysis is a new and denser velocity field, which is used to study the plate kinematics and the
rate of interseismic strain building across the Straits. GPS velocities show a sudden change in their orientation
across the Straits moving to NNW-ward, in Estern Sicily, to NNE-ward in Western Calabria, depicting this area as
a primary boundary between two different tectonic domains.
The maximum strain-rates observed across the Straits are about 120 nanostrain/yr, with extension oriented about
normal to the coasts of Sicily according to the presence of a normal fault. The measured velocity gradient can
be used to model the creeping dislocation at depth, however, over the Messina Straits the interseismic elastic
strains accumulating across other nearby active faults can significantly affect the observed velocity gradient.For
this reason we investigate, using a regional elastic block-modeling approach, these effects. We use the block model
to test for different microplates configurations and to account for nearby active faults while inverting for optimal
fault geometry and intersismic slip-rates across the Straits.

D’Agostino & Selvaggi, JGR, 2004
Serpelloni et al., GJI, 2007
Anzidei et al., J. Geodyn., 1998
Williams et al., JGR, 2004
Meade & Hager, JGR, 2005