Paleoseismology along the Cittanova fault: Implications for seismotectonics and earthquake recurrence in Calabria (southern Italy)

Abstract

This paper focuses on the seismogenic structure responsible for the 5 February 1783 earthquake (M > 7, Calabria, southern Italy), in particular the slip rate and recurrence time along the Cittanova fault, thus giving new insights on the seismic hazards and seismotectonics of the region. The 1783 earthquake, one of the strongest earthquake of the Mediterranean area, caused more than 30,000 casualties and radically changed the physiography of the local landscape. Until now, the Cittanova fault (or Aspromonte fault) has been generally identified as the surficial expression of the seismogenetic structure, even though its youthful activity has never been demonstrated. Recently, the shortage of geologic evidence of middle‐upper Pleistocene activity on this fault led some authors to locate the 1783 fault elsewhere. In our study we used a multidisciplinary approach (paleoseismology, geomorphology, historical seismology, archaeoseismology); our analysis of contemporary literary sources strengthened our interpretation of the coseismic origin of many geological features and, sometimes, oriented our field research toward specific areas. In particular, we excavated trenches and pits at three different sites along the trace of the Cittanova fault for paleoseismological analysis and 14C dating. Our data document the Holocene and present activity of the Cittanova fault, providing a minimum vertical slip rate of 0.44 mm/yr and a possible return time of 1350–1800 years for earthquakes similar to 1783. The penultimate event has been dated to the 4th century A.D., a time when southern Calabria and eastern Sicily were devastated by an earthquake documented by archaeoseismic analyses.

Low slip rates and multimillennial return times for Mw 7 earthquake faults in southern Calabria (Italy)

“…Our study on the recent activity of the CF completes and extends the results of Galli and Bosi [2002], revealing that the 1783 earthquake is not the only M w 7.0 event generated in historical times by this structure, as the CF Figure 5. Chronogram of the surface rupture events identified from within the trenches; each radiocarbon sample is reported with its 2σ calibrated interval (yellow, ante quem term; cyan, post quem term; orange, ad quem term; tile, archeological shard).…”

“…In turn, unit 3c, which unconformably lays over unit 6 in the footwall, postdates an episode of footwall erosion and scarp retreat likely related to a surface faulting episode. By comparing and cross matching these results with the radiocarbon dating of the faulting evidence in the previous trenches [Galli and Bosi, 2002], we can obtain a more robust framework of paleoseismic indication along the CF. Figure 5 contains the dated elements that constrain each single faulting event in the present trench (trench C2), the old excavations in Cittanova (trench C1), and across the Melone torrent site (trench M).…”

“…Prior to the 1783 faulting (Eq1), the penultimate event (Eq2) occurred between 235-405 A.D. and 385-535 A.D. This time span also fits the age of an epigraph mentioning a TERREMOTVS [Putorti, 1913] that damaged Rhegium few years before 374 A.D., as well as many other settlements of the region [Galli and Bosi, 2002]. As the modern Reggio Calabria was also struck by the 1783 earthquake (8-9 MCS degree), it is likely that the two events have been caused by the same fault in the third quarter of the fourth century A.D.…”

“…Some of these earthquakes have been paleoseismologically associated with known or newly identified faults ( Figure 1: June 1638 event to Lakes fault, LF; and the 5-7 February 1783 events to Cittanova and Serre faults, CF and SF, respectively) [Galli and Bosi, 2003;2002;Galli et al, 2007]. However, most of the faults involved in remain unknown or only tentatively related to proposed active faults [Monaco and Tortorici, 2000;Galli et al, 2007;Cucci and Tertulliani, 2010;Argnani, 2011].…”

“…Trenches across the CF [Galli and Bosi, 2002] provided clues for four earthquakes before the 1783 rupture. The last one was constrained within the fourth century A.D., whereas the others were indistinctly distributed in the Holocene, because of the lack of certain paleoseismic indicators (i.e., colluvial wedges: from here on CW.…”