Geoarchaeology and paleoseismology blend to define the Fucino active normal fault slip history, central Italy

Abstract

We first describe the late Holocene slip history of one of the major segments of the Fucino active normal fault, in central Italy, by combining geoarchaeological investigations with paleoseismological trenching. The Fucino fault system released a Mw 7 earthquake in 1915 (with many other events with decimetre and/or metre-size palaeoseismic slip events in the past), that is the strongest seismic shock occurred in this portion of the Italian territory over at least the past millennium. We dug trenches across the investigated tectonic structure; then, the sedimentary sequence and its relation with the exposed fault planes have been analysed “vertically”, as typically made in paleoseismological investigations, but also “horizontally”, by deepening the excavations “step-by-step” while digging, i.e. performing archaeological-type stratigraphic excavations. Such a procedure permitted the recognition of different displacement events of the fault, and the progressive surveying of different cultural levels, since the Neolithic Period, interposed with or cut into natural levels. The reconstruction of the interplay between human occupation of the site and the local geomorphic evolution e framed by the late Holocene climatic changes e permitted us to gain reliable chronological data for constraining the fault slip history in the last 5500 yr. Our analyses also confirmed that the investigated structure activated during the 1915 earthquake. Four previous displacement events were recognised: a first event, prior to the 1915 one, occurred slightly after the Roman Period (probably during the 5the6th century AD); two preceding events occurred between the Late Neolithic and the Roman period, the older of the two during the late Neolithic, while the later during the Late Bronze Age-Early Iron Age. The oldest event predates the Neolithic Period. No evidence of a Late Middle Ages faulting event found by others researchers along another branch of the Fucino fault was found in our trenches. From a methodological viewpoint, the results of our study mark the effectiveness of adopting joint geoarchaeological/paleoseismological approach in terms of chronological constraints for active faulting studies in such contexts where long human occupation took place, where the natural and “human” events rhythmically interplay.