The Tectonic Puzzle of the Messina Area (Southern Italy)
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The tectonic puzzle of the Messina area (Southern Italy): Insights from new seismic SUBJECT AREAS: TECTONICS reflection data ENVIRONMENTAL ECONOMICS Carlo Doglioni1, Marco Ligi2, Davide Scrocca3, Sabina Bigi1,3, Giovanni Bortoluzzi2, Eugenio Carminati1, GEODYNAMICS Marco Cuffaro3, Filippo D’Oriano2, Vittoria Forleo1, Filippo Muccini4 & Federica Riguzzi5 ASTRONOMY AND PLANETARY SCIENCE 1Dipartimento di Scienze della Terra, Universita` Sapienza, P.le A. Moro 5, 00185 Roma, Italy, 2Istituto di Scienze Marine, CNR, U.O.S di Bologna, Via Gobetti 101, 40129 Bologna, Italy, 3Istituto di Geologia Ambientale e Geoingegneria, CNR, c/o Received Dipartimento di Scienze della Terra, Universita` Sapienza, P.le A. Moro 5, 00185 Roma, Italy, 4Istituto Nazionale di Geofisica e 9 October 2012 Vulcanologia, Roma2, Via Pezzino Basso 2, 19020, Fezzano (La Spezia), Italy, 5Istituto Nazionale di Geofisica e Vulcanologia, Roma, Via di Vigna Murata, 605, 00143 Rome, Italy. Accepted 28 November 2012 Published The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of 13 December 2012 the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian Correspondence and offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina requests for materials Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction should be addressed to zone relative to slab advance in the western Sicilian side. M.C. (marco.cuffaro@ igag.cnr.it) or C.D. th (carlo.doglioni@ he Messina Strait and surrounding area are seismically active and responsible for the Mw 7.1 December 28 1,2 uniroma1.it) 1908 earthquake , with a related tsunami (run-up height up to 10 m), which caused more than 60.000 T casualties. Several earthquakes have struck the area over the centuries1–4. The area is highly populated and the longest single span ever built bridge has been planned to cross the Messina Strait (Fig. 1). In order to contribute to the understanding of the tectonic framework, we explored the area by a multichannel seismic reflection and multibeam survey (TIR10, cruise report available at http://www.ismar.cnr.it). A morphologic map and regional cross sections, based on these new data, allow us to image the upper 3–4 km of the crust of the area (Figs. 2, 3 and 4), adding information for the evaluation of the seismic risk in the area. The Messina Strait is an extensional feature, crosscutting the Apennines belt, and separating the Italian peninsula from Sicily (Fig. 1). It is located in the area between the Neogene Tyrrhenian backarc basin, developed in the hangingwall of the Apennines, and the Mesozoic-Paleogene Ionian basin, which is the foreland and the area of propagation of the Neogene to present Apennines thin-skinned accretionary prism5,6. The Messina Strait is part of the transitional zone separating the faster SE-retreating slab beneath Calabria and the Sicilian continental lithosphere7–9. The main transition runs along the northward prolongation of the Malta Escarpment (west of the Messina Strait), that separates Calabria to the east, moving SE-ward relative to Sardinia (Eurasia), whereas to the west of the escarpment, the Sicilian microplate converges NW-ward with respect to Sardinia10. This different behaviour is marked particularly by the subduction hinge which is moving away with respect to the upper plate (i.e., Sardinia) along the Calabrian side, whereas it converges relative to Sardinia in the Sicilian side of the subduction zone11. This is coherent with the contractional setting in the northern Sicilian offshore12,13. The Messina Strait is shaped by a complex network of normal and transtensional transfer faults14–18 (Fig. 1 and Fig. 2), that may have a multiple origin: 1) extension associated with the back-arc spreading, contemporaneous and genetically linked to the Apennines slab retreat; 2) mantle wedging and uplift of the Apennines belt; 3) faster differential SE-ward retreat of the Calabrian slab relative to the Sicilian slab; 4) lengthening of the Apennines arc associated to the radial slab retreat. The Strait is located on the upper plate crust, that is ,26 km thick19, and composed by a stack of Alpine and Hercynian metamorphic basement slices overlain by Oligo- Miocene terrigenous sequences, SE-thrust on non-metamorphic Meso-Cenozoic sedimentary successions14,20. A Miocene-Quaternary marine sequence rests unconformably on this complex and is similar across the two sides SCIENTIFIC REPORTS | 2 : 970 | DOI: 10.1038/srep00970 1 www.nature.com/scientificreports Figure 1 | Geological setting of the Messina Strait, with location of the planned bridge (gray solid line), and of the seismic reflection profile TIR10/01 (white line). This area is shaped by a complex network of normal and transtensional faults (black lines with ticks). Depth of the top of the subducted Ionian slab (ref. 38 and references therein) is also shown (black lines). Red, blue and green dots are earthquake epicentres38, occurring at depths , 15 km, between 15 and 35 km, and . 35 km, respectively (http://csi.rm.ingv.it). Focal plane solutions are from ref. 39. Red arrows indicate GPS velocity vectors10. Black rectangle is the survey area of Fig. 2. Lower-right panel shows a tectonic sketch of the southern Tyrrhenian Sea, representing coexisting compression (solid red arrows) along the northeastern Sicilian offshore, and extension (open red arrows) in southern Calabria. of the Strait, although thickness variations occur from Calabria to where normal faults show evidence of recent activity. In particu- Sicily. In Calabria it includes ,300 m of Tortonian sandstones and lar, along the Sicilian coast, close to Messina, the MIS 5.5 terrace clays and Lower Pliocene marls (Trubi Formation), unconformably (about 125 kyr) is located at 90 m a.s.l., while in the Villa San covered by i) Upper Pliocene-Lower Pleistocene marine clays and Giovanni area (on the Calabrian coast) it is uplifted up to 170 m sands (40–150 m thick20); ii) Middle-Upper Pleistocene marine a.s.l.24. In Supplementary Fig. S1 are shown the average uplift rates clays, calcarenites and calcareous sands, ,100 m thick20. The inferred from the MIS 5.5 terrace. The differential uplift implies Pleistocene Messina sands and conglomerates (200–400 m thick) active tectonics in the Strait. The morphology of the north-eastern lie unconformably both on the thrust sheets and on the Miocene- part of the strait depicts an ENE-trending graben, although deep Pleistocene sequence. These deposits contain Gilbert fan deltas21, geometries indicate an asymmetric feature. The recent faults in the prograding toward the Messina Strait from the Calabrian and the area are arranged in two broad ,ENE-trending arrays with Sicilian coasts, indicating that they were deposited into an already opposing polarity separated by a NW-trending transfer zone opened graben, pre-dating it. They have been correlated to the uplift located between Messina and Reggio Calabria24,25. Moving south- processes affecting the flanks of the Strait in the last 0.7–1 Ma (0.5– ward, the Strait trends more N-S, and kinematically a right-lateral 1.2 mm/yr, ref. 24). transtensional component is expected as proposed by ref. 26 and The occurrence of large active faults has been inferred based on supported by the present GPS data. This is consistent with the the uplift of the Pleistocene marine terraces along the coast of the faster SE-ward retreat of the Apennines-Calabrian subduction Strait, where five to twelve orders of different age terraces have with respect to Sicily11, which implies a right-lateral transtension been identified17,22,23. Uplift was faster in the Calabrian sector, in between. SCIENTIFIC REPORTS | 2 : 970 | DOI: 10.1038/srep00970 2 www.nature.com/scientificreports Figure 2 | Morpho-structural map of the Messina Strait, with location of the scarp of the Capo Peloro fault, of the blind Messina Strait Fault (dashed black line), and of the Scilla Fault System. The adjacent anticline to the north is located at the eastern tip line of the Capo Peloro fault. The fold axis to the northeast is en-e´chelon with respect to the E-W-trending right-lateral transpression offshore northern Sicily, and slightly en-e´chelon with respect to the Capo Peloro fault. The white lines indicate locations of seismic profiles, with shot points, TIR10/01, TIR10/07 and TIR10/09 (Figs. 3 and 4, Supplementary Figs. S2, S8, S9 and S10). The thick grey and black dashed lines indicate the planned bridge and the cross section shown in Fig. 6, respectively. Results the adjacent anticline (Fig. 2), suggesting activity, possibly with The seismic section of Fig. 3 shows an indistinct basement higher displacement rates. The Capo Peloro fault dips steeply to (Hercynian metamorphic rocks and possibly Mesozoic cover, over- the SSW, and its geometry suggests both reverse and strike-slip printed by Alpine deformation) and a Pliocene-Pleistocene sedi- components. However the horizontal component is unconstrained, mentary sequence (mostly siliciclastic) covering a widespread but it could be represented by the shortening accommodated by the unconformity that can be ascribed to the Messinian sea-level drop27. anticline to the northeast of the Capo Peloro fault (Fig. 3) which is The entire Plio-Pleistocene sequence is cross cut by a major fault, the accounting for a shortening .500 m when cross-section balanced Capo Peloro fault, with an offset of the basement top of about 325 ms technique is applied.