Teleseismic tomography of the southern Tyrrhenian subduction zone: New results from seafloor and land recordings

Abstract

[1] Teleseismic traveltime data, recorded by temporary ocean bottom seismographs deployed in Tyrrhenian Sea around the Aeolian Islands (Tyrrhenian Deep-sea Experiment (TYDE)), have been used for the first time in Italy to refine the 3-D model for the deep P wave velocity structure of the southern Tyrrhenian subduction zone. The arrival times of 35 teleseisms have been combined with those recorded by the Italian National Network. In order to obtain a more complete azimuthal coverage of teleseismic rays, 80 events recorded by land stations from 1990 to 2002 have been included in the data set. In total, 2904 P and 314 PKPdf phases, 1300 recorded by ocean bottom instruments, have been collected. The upper mantle structure is reconstructed down to 500 km by a nonlinear inversion of the relative residuals computed with respect to the reference 1-D velocity model ak135. The obtained tomographic model has a higher resolution than those previously published thanks to the recordings of TYDE seafloor stations. Tomographic results confirm the presence of the Tyrrhenian slab imaged as a high-velocity body extending from the uppermost mantle down to the bottom velocity model with dip 70-75°NW. The model better defines the geometry of the seismogenic part of the slab. Its lateral extension is about 200 km in the depth interval 150-300 km, where most of the deep seismicity is concentrated. At uppermost mantle depths the fast structure has smaller lateral dimensions (about 100 km). The inversion also points out a wide well-resolved low-velocity zone completely surrounding the steeply dipping fast structure from the lower crust down to about 300 km. This feature suggests the presence of a threedimensional circulation of asthenospheric flow around the Ionian slab caused by retreat and roll-back of the slab. Our results are in agreement with recent laboratory experiments, mantle anisotropy studies, geochemical and isotopic analyses, and modeling based on residual topography.Citation: Montuori, C., G. B. Cimini, and P. Favali (2007), Teleseismic tomography of the southern Tyrrhenian subduction zone: New results from seafloor and land recordings,

Evolution of the southern Tyrrhenian slab tear and active tectonics along the western edge of the Tyrrhenian subducted slab

“…This pattern of recent deformation is compatible with GPS-derived strain-rate axes Argnani et al 2007) and with stress field obtained from focal mechanisms (e.g., Neri et al 2005).…”

“…4). Focal mechanisms have recently shown the occurrence of a compressional belt located in the southern Tyrrrhenian Sea, north of Sicily (Pondrelli et al , 2006Vannucci et al 2004;Neri et al 2005). P axes mostly trend North-West to NNW-SSE, except in the central Aeolian Islands, a direction in good agreement with the Nuvel-1 global motion of Africa relative to Europe (DeMets et al 1990).…”

“…GPS data and earthquake focal mechanisms indicate active NNW-SSE compression in the SW Tyrrhenian region and NW -SE extension in the SE Tyrrhenian and Calabrian region (Hollenstein et al 2003, D'Agostino & Selvaggi 2004Pondrelli et al 2004Pondrelli et al , 2006Neri et al 2005;Serpelloni et al 2007;Argnani et al 2007); the transition between the two domains occurring in the central Aeolian region.…”

“…Chiarabba et al 2005) and P-wave seismic tomography (Lucente et al 1999;Wortel & Spakman 2000;Piromallo & Morelli 2003;Spakman & Wortel 2004;Montuori et al 2007) support the occurrence of a deep and narrow Ionian slab located beneath Calabria. On the other hand, P-wave seismic tomography suggests that lithospheric slab is absent underneath Sicily and the southern Apennines, to support the occurrence of slab tears affecting the subducted African lithosphere (e.g.…”

Magmatic diversity of western Mexico as a function of metamorphic transformations in the subducted oceanic plate

“…The unique combination of geologic parameters of the Mexican subduction zone will be hardly documented in other places, but some resemblance exists in southern Italy, where the Ionian oceanic lithosphere rests at 200 km beneath Aeolian volcanoes like Stromboli, which displays a petrological diversity that is similar to that of the western TMVB (Gvirtzman and Nur, 2001;Francalanci et al, 2007;Montuori et al, 2007;Tommasini et al, 2007). Nevertheless, the Ionian slab is very old, rich in sediments, and one of the coldest on Earth, and is only comparable to Rivera by its high dipping angle (Pasquale et al, 2005).…”