The subduction structure of the Northern Apennines: results from the RETREAT seismic deployment

Abstract

The project Retreating-trench, extension, and accretion tectonics, RETREAT, is a multidisciplinary study of the Northern Apennines (earth.geology.yale.edu/RETREAT/), funded by the United States National Science Foundation (NSF) in collaboration with the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Grant Agency of the Czech Academy of Sciences (GAAV). The main goal of RETREAT is to develop a self-consistent dynamic model of syn-convergent extension, using the Northern Apennines as a natural laboratory. In the context of this project a passive seismological experiment was deployed in the fall of 2003 for a period of three years. RETREAT seismologists aim to develop a comprehensive understanding of the deep structure beneath the Northern Apennines, with particular attention on inferring likely patterns of mantle flow. Specific objectives of the project are the crustal and lithospheric thicknesses, the location and geometry of the Adriatic slab, and the distribution of seismic anisotropy laterally and vertically in the lithosphere and asthenosphere. The project is collecting teleseismic and regional earthquake data for 3 years. This contribution describes the RETREAT seismic deployment and reports on key results from the first year of the deployment. We confirm some prior findings regarding the seismic structure of Central Italy, but our observations also highlight the complexity of the Northern Apennines subduction system.

Peeking inside the mantle structure beneath the Italian region through SKS shear wave splitting anisotropy: a review

“…The great improvement on SKS shear wave splitting measurements has been possible thanks to two NSF Projects: RETREAT (Retreating-TRench, Extension, and Accretion Tectonics) and CAT/SCAN (Calabria-Apennines-Tyrrhenian/Subduction-Collision-Accretion Network). The RETREAT Project [Margheriti et al, 2006], focused in Northern Apennines, consisted in the installation of 50 temporary seismic stations, at which seismic anisotropy was measured together with data from several local permanent stations belonging to the Italian National network [INGV Seismological Data Centre, 2006]. The SKS splitting measurements allowed to identify two different anisotropic domains with different patterns, a Tyrrhenian and an Adriatic one [Plomerová et al, 2006;Salimbeni et al, 2007;, mostly related to different mantle deformation patterns above and below the slab.…”