Letters Insights into the evolution of the Italian lithospheric structure from S receiver function analysis Meghan S. Miller a,n , Nicola Piana Agostinetti b a Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, MC 0740, Los Angeles, CA 90089-0740, USA b Istituto Nazionale di Geofisica e Vulcanologica, Centro Nazionale Terremoti, Rome 00143, Italy article info Article history: Received 15 November 2011 Received in revised form 5 June 2012 Accepted 7 June 2012 Editor: P. Shearer Keywords: lithosphere–asthenosphere boundary subduction zone evolution receiver functions lthospheric structure abstract To advance our understanding of the complex and episodic tectonic history of the central Mediterra- nean, we image the characteristics and structure of the convergent African and Eurasian lithospheric plates using S receiver functions. Specifically we investigate the lithospheric structure in terms of seismic velocity discontinuities, including the crust–mantle boundary (Moho) and the lithosphere– asthenosphere boundary (LAB) beneath Italy. The geometry and continuity of these structures are explored using teleseismic S-to-P converted phases, applied extensively throughout this region for the first time. The continental lithospheric thickness varies between 60 and 170 km with an average of 90 km, and the pulse characteristics of the converted phases can be characterized by tectonic region and history. Beneath the Northern Apennines, where subduction is still active, we find evidence for a complex lithospheric structure, where two different negative S-velocity jumps are present at approximately 90 and 180 km depth. The shallowest negative phases are interpreted as the base of the lithosphere, but the second negative phases are much deeper than expected for the overriding plate lithosphere. When compared to hypocenter locations and P-wave tomography these deep converted phases correlate with the base of fast velocities perturbations in the upper mantle and regions with subcrustal earthquakes. In contrast beneath the Southern Apennines, the lithospheric structure appears less complex, with only one significant negative arrival in the receiver functions and where no subcrustal earthquakes are present. These pulses are generally deeper ( 110 km) than those beneath the Northern Apennines and are broader in shape indicating a less sharp velocity contrast. Farther south along the Italian peninsula, the structure becomes complex again, with two sharp negative amplitude phases at depth. These deep converted phases that originate in the uppermost mantle beneath the Calabrian arc and Sicily are also co-located with deep ( 435 km) earthquakes. These observations suggest that these deepest negative phases correspond to the base of the actively subducting lithosphere beneath the Northern Apennines and Calabria, and where these phases are absent in the receiver functions there is no subducting slab. Seismic imaging of the lithosphere and uppermost mantle using S-to-P conversions provides another geophysical dataset to aid in interpretation of the complex, segmented slab structure beneath Italy. & 2012 Elsevier B.V. All rights reserved. 1. Introduction More fully understanding the structure and dynamics of litho- sphere, the relatively rigid outer shell of the Earth, as it subducts along arcuate plate boundaries aids in constraining mantle processes. Subduction zone evolution is affected by physical properties, composition, extent and formation of the incoming plate. Furthermore, the lithospheric structure of the overriding plate is strongly influenced by processes such as convergence rate and direction. Therefore, delineating the lithospheric structure of the two interacting plates can provide important constrains on the behavior of late stage convergent margins. The Mediterranean has undergone an irregular, complex temporal evolution with episodic rollback and retreat of the subducted plate followed by period of slow trench-migration (i.e. Malinverno and Ryan, 1986; Dewey et al., 1989; Faccenna et al., 2001; Rosenbaum and Lister, 2004). The complicated tectonic history of the region is a result of the convergence of Eurasia and Africa and subsequent closure of the Tethys Ocean starting at about 140 My. Prior to the Oligocene, convergence was primarily accommodated by subduction of oceanic lithosphere along the southern Eurasia margin, but then transitioned from subduction dominated to continental collision dominated Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/epsl Earth and Planetary Science Letters 0012-821X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2012.06.028 n Corresponding author. Tel.: þ1 213 740 6308; fax: þ1 213 740 8801. E-mail addresses: msmiller@usc.edu (M.S. Miller), nicola.piana@ingv.it (N. Piana Agostinetti). Earth and Planetary Science Letters 345–348 (2012) 49–59