ANALISI PALEOSISMOLOGICHE LUNGO LA FAGLIA DEL M. MARINE (ALTA VALLE DELL’ATERNO): RISULTATI PRELIMINARI

Abstract

Paleoseismological analyses along the Mt. Marine Fault (High Aterno Valley): preliminary results.The south-western side of Mt. Marine
is characterized by a NW-SE trending normal fault, which has been responsible for the formation of the Alto Aterno intermontane basin.
This area was affected by the earthquake of 2 February 1703 (Me=6.7), which represents the last seismic event of a sequence characterized by two other main earthquakes occurred during January 1703.
During investigations aimed at realizing a “Prototipe Geological Map”, some fault scarps (WNW-ESE trending), have been recognized
at the base of Mt. Marine; these scarps are related to the recent fault activity. The identification of the fault scarps suggested to perform paleoseismological analyses in the area. A trench was dug across the 10-m-high southernmost scarp. On the basis of the sedimentological and paleoenvironmental characteristics, the stratigraphic sequence recognized within the trench was divided in 4 different complexes, separated by 3 fault zones. The different ages of the defined complexes has been confirmed by the results of the radiocarbon analysis. Paleoseismological analyses indicate the occurrence of a minimum of five displacement events within the last 15,000 years; the most recent of these events is probably related to the 2 February 1703 earthquake, as indicated by the displacement of historical colluviums and by the historical information on the geological coseismic effects in the investigated area. Displacements observed along the secondary faults of the main fault zones vary between 0.10 and 0.60 m. Considering the magnitude (Me=6.7) associated with the 2 February 1703 earthquake and on the basis of the empirical relationships between earthquake magnitude and surficial displacement, a maximum displacement per event of about 1 m can be expected. Paleoseismological studies provided, therefore, further information about the association between the 1703 seismic event and the Mt. Marine fault. Also the magnitude related to this event (Me=6.7) is comparable with the Mw (6.7) which can be derived from the equations linking this kind of magnitude with the length of the surficial fault expression of the entire L’Aquila fault system (about 25 km).