Seismic anisotropy beneath the Northern Apennines (Italy): Mantle flow or lithosphere fabric?

Orogen-parallel variability in 3D seismicity distribution, Northern Apennines (Italy): Evidence for a slab tear fault?

“…Present-day stress regime as inferred from regional CMT focal solution, clearly displays a compressional area along the Adriatic coast, juxtaposed to an extensional area distributed along the southwestern side (Pondrelli et al, 2011;see Fig. 2), where Neogenic extensional basins complex approaching the orogens, pointing against the simple, uniform retreat of the whole subducted slab (Salimbeni et al, 2008;Plomerová et al, 2006). Images of teleseismic body wave attenuation provide a further evidence of the complexity of the subduction pattern, displaying a strong lateral heterogeneity in both P and S wave quality factors along the North Apenninic chain (Piccinini et al, 2009).…”

The AlpArray Seismic Network: A Large-Scale European Experiment to Image the Alpine Orogen

“…Solving this controversy is particularly relevant for the Friuli seismic hazard area, which is located either in the foreland (if the slab beneath the Eastern Alps is Adriatic) or in the hinterland of the Alps (if the slab beneath the Eastern Alps remained European). In general for the entire region, the determination of mantle seismic anisotropy patterns helps to reconstruct the current and past plate motions and dynamics in three dimensions; the broad coverage with the uniform AASN will allow a more comprehensive analysis with respect to previous studies often focused on smaller areas (Margheriti et al 2003;Plomerová et al 2006;Kummerow et al 2006;Fry et al 2010;Barruol et al 2011;Salimbeni et al 2013;Qorbani et al 2016;Subašić et al 2017).…”

“…Subsequent campaigns (see location examples in Fig. 2) often aimed at crustal, lithospheric and upper mantle depths by various passive seismology methods, all along the Alpine arc from the West (e.g., French Massif Central: Granet et al 1995;CIFALPS: Zhao et al 2015) and Northwest (EIFEL: Ritter et al 2000;TIMO: Ritter et al 2009), through the Central Alps (ALPASS: Brückl et al 2005; TRANSALP: Kummerow et al, 2004) to the Eastern termination (e.g., CBP project: Hetényi et al 2009Hetényi et al , 2015Dando et al 2011;Ren et al 2013), in the Apennines to the South of the Alps (GeoModAp: Amato et al 1998; RETREAT, e.g., Plomerová et al 2006;Margheriti et al 2006;Munzarová et al 2013) and in the Bohemian Massif adjacent to the Alps on its northern side (MOSAIC: Plomerová et al 2005; BOHEMA, e.g., Karousová et al 2013;PASSEQ: Wilde-Piórko et al 2008;Eger Rift, e.g. Geissler et al 2005; KW: Bianchi et al 2015).…”

Theory and Observations - Seismic Anisotropy

“…This hypothesis has been confirmed by splitting observations in South America (Polet et al, 2000;Russo and Silver, 1994), Kamchatka (Peyton et al, 2001), and the Apennines (Margheriti et al, 2003;Plomerova et al, 2006). However, Song and Kawakatsu (2012) had argued that subslab anisotropy can be fossil, caused by strong VTI anisotropy with a slow axis of symmetry in asthenosphere that becomes entrained with the downgoing slab.…”

“…In cases where continental tectonics is active, mantle flow from present-day tectonics can be clearly evident (Becker et al, 2003) but superimposed on mantle textures inherited from terrane formation and assembly. On the Adriatic and Ionian side of the Apennines orogen, Margheriti et al (2003) observed orogen-parallel fast polarization over much of the Italian Peninsula and Sicily, but at the northern end near the Po Valley, the influence of anisotropy in the Paleozoic basement rocks complicates an interpretation in terms of mantle flow (Plomerova et al, 2006). In the Arabian Plate, the fast SKS polarization aligns with a late Proterozoic collisional zone Wolfe et al, 1999), but Hansen et al (2006) argued that this splitting is caused by present-day asthenospheric flow deflected from the Red Sea Rift.…”