Catastrophic 1638 earthquakes in Calabria (southern Italy): New insights from paleoseismological investigation

Abstract

The reanalyses of all the primary historical sources of the catastrophic March–June 1638 Calabrian earthquakes permitted to split up the seismic sequence in different events that occurred in conterminous areas and to direct our geological surveys of the June shock inside the Sila massif (northern Calabria). We carried out paleoseismological analyses along the Lakes fault (LF), a previously unknown fault. LF (trending NW‐SE) cuts the eastern sector of the Sila massif and dips southwestward, damming the drainage network that runs toward the Ionian Sea. We opened four trenches close to or inside some of the small marshes and ponds created by the footwall uplift, finding evidence of several displacement events, the last one being the June 1638 earthquake (M = 6.7). The fault location fits with the historical description of a long fracture opened during the event, our trenching area being still named by the natives “the earthquake sag.” The young geomorphic expression of LF recalls that of the 1980 Irpinia fault, suggesting its relatively recent activation within the extensional regime characterizing the Calabrian arc. Conversely, the northern continuation of LF (Cecita Lake fault), which we argue to be active too, is not associated to any historical earthquake of the Italian seismic catalogue, this fact evidencing a long, at least 1000 years, elapsed time. Our study permits (1) the relocation of the June 1638 earthquake inside the Sila massif, the epicenter being shifted with respect to the macroseismically derived one, (2) the revision of the whole 1638 sequence, (3) the discovery of the LF, (4) the recognition of the evidence of the June 1638 surface faulting plus four previous paleoearthquakes, and (5) the evaluation of its slip rates and return interval. Finally, the relationship of LF with the neighboring faults casts light to the seismotectonic of the region, providing a new insight to the seismic hazard analysis.

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

“…This deformation, although much lower than in centralsouthern Apennine (2-3 mm/yr; Figure S1), documents that this portion of the CA is not migrating rigidly relative to Ionian lithosphere (i.e., at 2 mm/yr) [D'Agostino et al, 2011] but deforms internally. Moreover, here the extension driven by the CF parallels the regional dip direction of the Ionian slab and of the trenchward motion (Figures 1 and S1), a situation differing from the northern CA where the extension is oblique [Galli and Bosi, 2003;D'Agostino et al, 2011] (LF in Figures 1 and S1). Therefore, a possible geodynamic explanation for the crustal extension accommodated by the southern Calabria faults (CF and SF in Figures 1 and S1) and to the associated earthquakes is the still active eastward rollback of the Ionian lithosphere, with the measured geologic extension rate partly reflecting the present-day, residual Tyrrhenian back-arc opening.…”

“…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].…”

“…These earthquakes include some of the strongest to ever occur in the Italian Peninsula (27-28 March 1638: M w 6.8-6.6; 9 June 1638: M w 6.7) [Galli and Bosi, 2003] (5 November 1659: M w 6.6) [Guidoboni et al, 2007] (Figure 1). After a century of seismic calm, the 1743 M w 5.9 event hit southern Calabria , preceding by 40 years one of the most catastrophic sequence in Europe.…”

Geomorphological map of the Crotone Province (Calabria, South Italy)

“…Notwithstanding the recent tectonic activity of the study area (Galli and Bosi, 2003), tectonic landforms are not easy to distinguish from structurally-controlled features. From a morphological point of view, the evidence of fault systems is represented by fault scarps responsible for the displacement of relics of the planation surfaces at different elevations.…”

The Crati River Basin: geomorphological and stratigraphical data for the Plio–Quaternary evolution of northern Calabria, South Apennines, Italy

“…In particular, the Crati Basin ( Fig. 1) developed in the subsiding hangingwall of the Crati fault system (sensu Spina et al 2011), one of the active and segmented normal fault systems of Calabria (Tortorici et al 1995;Galli & Bosi 2003;Tansi et al 2005;Spina et al 2009). …”