Paleoseismicity of the San Demetrio ne’ Vestini fault (L'Aquila Basin, Central Italy): Implications for seismic hazard

Abstract

The San Demetrio fault is a NW-SE trending normal fault at the south-eastern tip of the L'Aquila Basin fault zone (Central Apennines, Italy). Detailed field surveys and geophysical investigations, performed in the frame of seismic microzonation studies after the 2009 L'Aquila earthquake in the San Demetrio ‘ne Vestini territory, have clearly indicated that it is a capable fault.This paper illustrates the results of paleoseismic investigations along this fault, confirming its capability. At least five surface faulting events took place during the Holocene and latest Pleistocene, with variable offsets from a few centimetres (four events, the latter one most likely occurred in historical time) to about 50 cm (one event occurred between 16,430–16010 BCE and 7030–6570 BCE). These results are consistent, in terms of displacement per event, with the paleoseismic data collected on adjacent faults (i.e., the Paganica, Roccapreturo, Mt. Pettino and Mt Marine faults).Concerning seismic hazard, being the San Demetrio fault the southeastern tip of the L'Aquila fault system, its Holocene reactivations should be associated to paleoearthquakes with epicentre located to the northwest centered in the L'Aquila basin, and minimum magnitude ranging between 6.0 and 6.3. Elsewhere, considering its position close to the transfer zone to the Subequana Valley faults system, another option is that surface faulting is sympathetic to larger ruptures produced by the reactivation of this latter faults system.Based on fault scaling relationships, the offset of 0.5 m occurred before the Holocene may indicate an earthquake of M > 6.5, never replicated afterwards on the San Demetrio fault.