Tomographic constraints on the geodynamic evolution of the Italian region

Abstract

Abstract. In this paper we present P wave tomographic images of the mantle beneath Italy obtained by inverting -6000 teleseismic P and PKP wave arrival times, accurately repicked, recorded in the time period 1988-1994 by the stations of the National Seismic Network of the Istituto Nazionale di Geofisica. We pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set. The data were inverted with the well-established Aki-Christofferson-Husebye tomographic technique; different reference models and residuals computation have been tried to verify the stability of the results. The high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the Alps and the Apennines, looking for their lateral and vertical continuity down to 800 km depth. The main finding of this study is a continuous high-velocity body located between 250 and 670 km depth beneath the entire Apenninic system dipping toward the Tyrrhenian area, which continues upward segmented in two main anomalies in the northern Apenninic and the Calabrian Arcs. We interpret this high-velocity feature as the subducted oceanic lithosphere between the Eurasian and African plates, dipping down to the upper-lower mantle boundary beneath the Tyrrhenian Sea. The retrieved images of the lithosphere subducting beneath Apennines are reliable in terms of thickness (about 80-90 km) and P wave velocity contrast (2-4% higher than the normal mantle). Furthermore, our tomographic images, which focus on the deep geometry and continuity of the velocity structures, provide new keys to understanding the geodynamic evolution of the Italian region. The segmentation of the high-velocity slab upward suggests a complex evolution of the arctrench system and the initially continuous subduction of the Ionian-Adriatic plate progressively developed in subordinate arcs, probably due to lateral heterogeneity of the subducting lithosphere.

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

“…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.…”

Constraints on mantle circulation around the deforming Calabrian slab

“…At 400 -600 km depth (Figure 3), the Calabrian fast anomaly merges into a broader positive anomaly, spreading over the Central Mediterranean [Piromallo and Morelli, 2003]. The Calabrian slab mostly had a SE-NW profile, where the high velocity structure can be followed continuously from a shallow region on the Ionian side of the arc, down to the 660 km discontinuity [Lucente et al, 1999]. The 3D view and the longitudinal section (Figures 3 and 5) show that the Calabrian slab is presently reduced to a narrow, finger-like, structure.…”

Deformation pattern of the 6 and 7 April 2009, <i>M</i><sub>W</sub>=6.3 and <i>M</i><sub>W</sub>=5.6 earthquakes in L'Aquila (Central Italy) revealed by ground and space based observations

“…During the Upper Miocene-Lower Pliocene, extension and accretion of new oceanic crust occurred in the Tyrrhenian Sea west of Italy (Lucente et al, 1999). Active subduction of the Ionian sea beneath Calabria was occurring at the same time with a progressive eastward migration of compressional fronts (Malinverno and Ryan, 1986).…”