The Contribution of Regional Uplift and Coseismic Slip to the Vertical Crustal
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B06401, doi:10.1029/2006JB004473, 2007 Click Here for Full Article The contribution of regional uplift and coseismic slip to the vertical crustal motion in the Messina Straits, southern Italy: Evidence from raised Late Holocene shorelines Luigi Ferranti,1 Carmelo Monaco,2 Fabrizio Antonioli,3 Laura Maschio,1 Steve Kershaw,4 and Vladimiro Verrubbi3 Received 22 April 2006; revised 13 December 2006; accepted 5 January 2007; published 7 June 2007. [1] Detailed mapping and dating of raised Late Holocene shorelines in southern Calabria, central Mediterranean region, reveals that the superposed shoreline record of uplift has both steady and abrupt components. Analysis reveals quantitative constraints may be applied to displacement partitioning between regional and fault-related sources in a context dominated by forearc uplift and extension above a retreating slab. Rapid displacements of arguable coseismic origin occurred at 1.9 and 3.5 ka and possibly at 5 ka and show a consistent site value, pattern of along-strike variation, and recurrence time (1.6 ka). The source of the rather large (1.5–2.0 m) slip per event based on the raised shoreline is not directly known and tentatively coincides with the Scilla extensional fault, which is inferred to run largely offshore. Although large uncertainties exist on the trace location, length, and seismogenic potential of the fault, our findings suggest that a substantial fraction of Holocene displacement is accommodated by coseismic footwall uplift. Precise compensation for sea level changes constrains Late Holocene steady uplift during the interseismic intervals at 1 mm/yr, a value consistent with long-term (0.1–1 Ma) estimates of regional uplift. Thus, Late Holocene total uplift of a 20-km stretch of coastline at 1.6–2.1 mm/yr is nearly equally balanced between regional and coseismic components. Appraisal of the present elevation attained by a suite of 125 ka and younger marine terraces indicate that rapid net uplift occurred in two episodes: (1) 100–80 ka and (2) after 5 ka; given the constancy in regional uplift rate, the two episodes are attributable to enhanced fault slip rate. Efficient seismic strain release was clustered in intervals of 10–20 ka and intercalated with a 80-Ka-long period of fault quiescence. Citation: Ferranti, L., C. Monaco, F. Antonioli, L. Maschio, S. Kershaw, and V. Verrubbi (2007), The contribution of regional uplift and coseismic slip to the vertical crustal motion in the Messina Straits, southern Italy: Evidence from raised Late Holocene shorelines, J. Geophys. Res., 112, B06401, doi:10.1029/2006JB004473. 1. Introduction which, within plate convergence zones, typically occurs in the overriding plate above retreating slabs [e.g. Elsasser, [2] The net vertical displacement of the Earth’s crust 1971; Funiciello et al., 2003; Schellart et al., 2003; Stegman results from the summed contribution of different sources, et al., 2006]. Within extensional settings, however, sedi- which can be regarded either as regional or local. Within ments or water infill often prevent a direct observation of the plate boundaries and mobile belts, the most obvious local displacement record. On the other hand, in extensional sources are represented by faults, which, opposite to regional provinces which experience regional uplift, the syntectonic strain, accommodate instantaneous displacements. Whereas record might be exposed and offers a chance to characterize thrust faults account for dominant uplift in contractional the sign and magnitude of motion accommodated on local belts, subsidence is a common product of normal faults, structures. Even under this favorable circumstance, accurate quantification of the relative contribution of far-field and 1 Dipartimento di Scienze della Terra, Universita` di Napoli Federico II, fault-related sources to the net vertical displacement of the Naples, Italy. 2Dipartimento di Scienze della Terra, Universita` di Catania, Catania, region is not obvious. The issue is further complicated by the Italy. ambiguity inherent in the timescale of comparison between 3Ente per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA), displacements on crustal faults, which may suffer frequent Casaccia, Rome, Italy. temporal fluctuations [e.g., Wallace, 1984; Slemmons and 4Department of Geography and Earth Sciences, Brunel University, Uxbridge, Middlesex, UK. dePolo, 1986; Grant and Sieh, 1994; Marco et al., 1996; Friedrich et al., 2003], and regional strains, which are Copyright 2007 by the American Geophysical Union. typically sustained over longer time spans. 0148-0227/07/2006JB004473$09.00 B06401 1of23 B06401 FERRANTI ET AL.: REGIONAL AND COSEISMIC UPLIFT, ITALY B06401 Figure 1. (a) Tectonic setting of southern Italy. Solid black line: Front of the contractional orogen in the Apennines and Sicily, solid teeth toward the orogenic belt [after the work of Bigi et al., 1992] and belt of contractional earthquakes in northern Sicily (empty teeth [after the work of Oldow and Ferranti, 2006]); dotted black lines: Depth (km) to the Benioff-Wadati zone of the Ionian slab [lines contoured after the work of Giardini and Velona`, 1988]; gray patches bounded by thick dashed lines: Parts of the Tyrrhenian Sea with Moho shallower than 15 and 10 km [after the work of Cassinis et al., 2003]; thin, solid gray lines: Uplift and subsidence rates (mm/year) in the Late Pleistocene [adapted from the work of Ferranti et al., 2006]. (b) Current deformation of the Calabrian Arc. Active faults (barbs on down-thrown side) after the studies of Stewart et al. [1997], Monaco and Tortorici [2000], and Catalano et al. [2003]; the double- arrowed line shows extension direction derived from fault kinematic analysis [after the work of Monaco and Tortorici, 2000] and contraction direction offshore northern Sicily based on fault-plane solutions. Focal mechanisms of moderate to large earthquakes (M > 4) after Harvard CMT [1976–2006] (http:// www.seismology.harvard.edu/CMTsearch.html) and Mednet RCMT [1997–2006] (http://mednet.ingv.it/ events/QRCMT/Welcome.html) catalogues [Pondrelli et al., 2002, 2004], Gasparini et al. [1985], and Anderson and Jackson [1987]. Epicenters of 1981–2002 instrumental seismicity from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) database (Castello et al., 2005, CSI, Catalogo della sismicita` italiana 1981–2002, versione 1.0. INGV-CNT, Roma, http://www.ingv.it/CSI/). Solid dots are tide stations at Tropea (T) and Reggio Calabria (RC). [3] Within the central Mediterranean area, the Calabrian places around the Messina Straits [Firth et al., 1996; arc, which includes southern Calabria on peninsular Italy Stewart et al., 1997; De Guidi et al., 2003; Antonioli et and the northeastern part of Sicily Island (Figure 1a), al., 2004], and the computed average uplift rates appear experienced large surface uplift since 0.8 Ma [Westaway, consistently higher than longer-term rates [Antonioli et al., 1993; Miyauchi et al., 1994; Monaco et al., 1996]. The 2006]. Although evidence exists for significant coseismic magnitude of Calabrian uplift is among the largest in the uplift at coastal sites in northeastern Sicily [Stewart et al., Mediterranean setting, and the 300 km wavelength of 1997; De Guidi et al., 2003], the role and magnitude of the uplifting province, in addition to its spatial coincidence fault-induced versus regional, steady displacement during with the location of a NW-dipping lithospheric slab Holocene uplift is, however, still poorly understood. (Figure 1a), clearly outlines its regional significance. [5] In this paper, we present a detailed study of raised Although located within a plate convergence zone, much Holocene shorelines on the eastern side of the Messina of the Calabria topography has been acquired during Straits, which offers an unprecedented opportunity to quan- extension [Ghisetti, 1984; 1992, Monaco et al., 1996], tify the relative contribution of local and regional sources to but the contribution of faulting to surface uplift is contro- total uplift and to characterize the absolute displacement of versial [e.g., Valensise and Pantosti, 1992; Westaway, fault blocks. Comparison of the Holocene uplift pattern with 1993; Catalano et al., 2003]. a longer (125 ka) uplift record, drawn from a flight of [4] Regional uplift, local slip rates, and macroseismic marine terraces, allows characterization of the temporal intensities are the greatest around the Messina Straits, the variations of uplift rates and provides vital insight into the narrow sea arm between Sicily and Calabria (Figure 1b), process of fault clustering [Slemmons and dePolo, 1986; where destructive pre- and historic earthquakes and devas- Marco et al., 1996; Friedrich et al., 2003]. Resolution of the tating tsunamis have left their record in the Scilla and Cariddi mode and magnitude of partitioning of vertical crustal myth [Virgil Marone, 1994]. In the last decade, displaced motion into local and regional components on the very Holocene shorelines have been investigated in several short timescale contributes to the understanding of the 2of23 B06401 FERRANTI ET AL.: REGIONAL AND COSEISMIC UPLIFT, ITALY B06401 seismogenic potential in the area and places constraints on together with seismicity depict an E-W trending belt of models of Calabrian arc uplift. This study also has wider contraction offshore northern Sicily (Figures 1a and 1b). significance because it provides clues to understanding the [9] The recent uplift of the Calabrian arc is spectacularly