GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.1 17 WHAT WAS THE ROLE OF FAULTS IN THE EVOLUTION OF THE MONTEREALE BASIN (CENTRAL APENNINE)? CONSIDERATIONS AND NON-EXHAUSTIVE ANSWERS E. Chiarini 1 , G. Nirta 1 , A. Sciortino 2 , M. Spadi 2 , M. Tallini 2 1 Servizio Geologico d’Italia – ISPRA. Roma, Italy 2 DICEAA - Università degli Studi dell’Aquila. Aquila, Italy The Montereale basin is the northernmost of the intermontane basins along the Aterno River. It is located in the tectonically active axial sector of the central Apennine between the Western Fault Systems (WFS) and the eastern ones (EFS; Galadini and Galli 2000). In the last two decades, these fault systems were the source for several earthquakes with magnitude Mw ≥ 6.0. The basin is a structural depression located in a complex tectonic context, between the western limit of the E-W oriented Gran Sasso ridge and the SSW-NNE oriented Olevano- Antrodoco thrust system. The basin is bordered to the NE by the Capitignano fault (CPF), while a second fault, the San Giovanni fault (SGF) is located in the center of the basin and seems to guide the formation of a sub-basin in the south-western sector (Fig. 1). The activity of the two faults has always aroused considerable interest because of their location between the active WFS and EFS, and for a long time represented an unsolved problem due to the lack of detailed studies on the quaternary stratigraphy of the basin. The SGF and CPF have been alternatively considered to be part of the Upper Aterno fault system in the WFS (Galadini and Galli 2000; Galadini et al. , 2000; Galadini and Messina, 2004), being part of the seismogenic source of the Laga Mt. fault in the EFS (Boncio et al. , 2004); or as a separate seismogenic source, capable of generating strong earthquakes (Lavecchia et al. , 2012). Over the past decades, the basin and the surrounding areas have been studied during the national geological mapping program (sheet n. 348-Antrodoco; Chiarini et al. , 2014; Servizio Geologico d’Italia, 2022) and seismic microzonation studies (Tallini, 2017; Nocentini, 2018). Instead, the mapping of SGF and CPF has been carried out in detail in the in recent years (2021- 2022) in the frame of the studies aimed at mapping the active and capable faults in the areas of the Montereale Basin that were affected by multiple seismic events since 24 August 2016 (Tallini et al. , 2021). The analysis of the LiDAR digital terrain model allowed a more detailed mapping, in some cases substantially different from what has been published so far (Civico et al. , 2016). The features recognized on the digital topography were then verified on the ground and structural data were collected on the exposed fault scarps. Thus, the fault traces were investigated by geophysical studies. A total of sixteen electrical resistivity tomographies (ERT), twelve across the CPF and four across the SGF, and two reflection seismic surveys across the CPF were performed. The results were integrated with the field data and the LiDAR analyses and allowed to choose the sites for three paleo-seismological trenches, one across the SGF and two across the CPF. The trench across the San Giovanni fault (Fig. 1) is placed in the hangingwall of the faults detected in the paleoseismological trenches dug by Cinti et al. (2018). The trench exposed a sedimentary succession resting on the limestone substrate. The upper Pleistocene deposits, with an age <40,000 years, are faulted by splay faults of the main structure with decimetric offsets while the substrate is displaced by about 3 meters. Two trenches were dug across the CPF, one at the base of the mountain front and one farther downstream (Fig. 1) to investigate a possible structure located within the Montereale basin. In the first case, the trench exposed faulted sediments, upper Pleistocene in age, while the arenaceous substrate shows a cumulative offset of about 2 m. In the second case, the upper Pleistocene sediments, that were investigated up to a depth of about 6 m, did not show clear faulting evidence.