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seismic microzonation (LeveL 3) of santa Lucia and capitignano (abruzzo region): first resuLts and considerations D. Berti1, E. Chiarini1, V. D’Andrea2, F. Durante2, E. La Posta1, L. Macerola2, M. Nocentini3, D. Palucci2, S. Silvestri1, M. Tallini2

1 ISPRA-Dipartimento per il Servizio Geologico D’Italia, Roma, Italy2 Dipartimento di Ingegneria Civile, Edile-Architettura e Ambientale (DICEAA), Università dell’Aquila, Italy3 Dipartimento di Scienze, Università di RomaTre, Italy

Introduction. The August 24, 2016 Mw 6.0 Central Italy earthquake, which has hit the Ascoli Piceno and Rieti provinces, has caused damages up to the northern L’Aquila Province. Indeed, damages were recorded at Santa Lucia village (municipality of Montereale) (IMCS= 6). The Capitignano territory, even if was assigned a macroseismic intensity (IMCS) equal to 5, is placed in the Quaternary Montereale basin characterised by several Seismic Hazard issues, such as surface active faulting, landslides (specifically debris flow and rock mass fall) and liquefaction (Gruppo di Lavoro INGV sul terremoto di Amatrice, 2016). Moreover, the Quaternary Montereale basin is the nearest Quaternary basin to the epicentral area of the August 24, 2016 earthquake. So that the Civil Protection Department involved ISPRA and DICEEA (L’Aquila University) for the Seismic Microzonation (Level 3) of Santa Lucia and Capitignano territory, including also Paterno and Piedicolle areas, to be used as prototype for the Abruzzo Region (Figs. 1 and 2).

Despite the distance from the epicenter, the serious consequences recorded in Santa Lucia could hypothetically depend by morphological and lithostructural seismic site effect considering obviously also the level of the building vulnerability.

The Capitignano territory is placed on a intramontane basin (Montereale basin) whose Quaternary evolution is controlled by the Capitignano and the S. Giovanni potentially active normal faults (Chiarini et al., 2014). Although none of the nine villages of the Capitignano municipality has had relevant damages, the amplification effects due to the basin sedimentary infill as well as the presence of two faults with Quaternary activity and earthquake prone landslides and liquefaction areas generate a relevant Seismic Hazard and are issues to be carefully analysed in the Seismic Microzonation (Level 3) prototype.

In recent years the Department of the Geological Survey of Italy - ISPRA covered both areas with geological surveys at a 1:10,000 scale for the 348 Antrodoco sheet of the official geological

map. The yet unpublished results of these surveys are the starting point of the study of the Seismic Microzonation (Level 3) of Santa Lucia and Capitignano.

Moreover, we took into account geological mapping such as the Seismic Microzonation (Level 1) (Abruzzo Region) of the municipalities of Capitignano and Montereale.

Geological setting. The SantaThe Santa Lucia and Capitignano villages lie along the tectonically active axial belt of the Apennine chain (northern Abruzzi, Central Italy), in a sector characterized by intense historical and instrumental seismic activity. They are placed at the Fig. 1 – Location map of Santa Lucia village.

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boundary between the Gran Sasso and the Laga tectono-stratigraphic domains, marked by the Gran Sasso thrust.

In the Santa Lucia area, placed within the Tronto River basin, surveys show the presence of a NE dipping monocline of arenaceous and arenaceous-pelitic lithotypes of the Messinian Laga formation; this structure is displaced to the west by a N240° dipping normal fault and crossed to the east by a N250° dipping thrust plane, belonging to the northernmost segment of the Gran Sasso thrust. On a local scale, the thrust is somewhere linked to low angle retro-verging compressive elements. This structural setting generates a widespread fracture pattern of bedrock lithotype giving rise to predisposing factors for amplification phenomena.

The north eastern villages of the Capitignano municipality were built on sandstone deposits of the Laga formation, which constitute a N240° dipping monocline structure locally affected by compressive elements, like vertical or overturned strata.

Instead, the main villages of the Capitignano municipality extend at the base of the north eastern mountain front of the Montereale basin (Chiarini et al., 2014) and are crossed by the main basin fault (Capitignano fault). They mainly rest on Quaternary alluvial fan deposits referable to several depositional events Middle Pleistocene to Holocene in age.

The Capitignano fault has been considered to be part of an active system (Boncio et al., 2004; Galadini et al., 2000; Galadini and Messina, 2004), responsible for the January 16 event (Mw= 6) during the 1703 seismic sequence (Blumetti, 1995; Boncio et al., 2004). According to Lavecchia et al. (2012) it reactivated during the seismic sequence following the main shock at L’Aquila on April 6, 2009 and forms with the San Giovanni Fault the Montereale Fault System that behaves as an individual source capable to release strong earthquakes.

At this time ISPRA is providing support to INGV for a mapping project (Civico et al., 2016) and paleoseimological studies on the San Giovanni and Capitignano faults.

Research carried out by ISPRA has identified within the intermountain basin two sedimentary sub-basins (Piedicolle and Capitignano), separated by a threshold Moreover, the evaluation of the thickness and the geometry of the Quaternary sedimentary infilling has been performed through a 3D analysis of survey data, borehole logs and geophysical data (Chiarini et al., 2014).

Task planning. Within the DPC activities after the Central Italy earthquake of August 24, 2016, the Seismic Microzonation (Level 3) of Santa Lucia and Capitignano have been organized into the following interconnected tasks:

Task 1: finding and storage into a GIS project of borehole logs and geotechnical and geophysical investigations;

Task 2: geological, geomorphological and building damage assessment surveys and mapping at a 1: 5,000 scale;

Task 3: elaboration of the technical-geological and seismically homogeneous microzones maps at 1:5,000 scale with related cross-sections; study of the seismic prone unstable areas

Fig. 2 – Location map of the Capitignano-Paterno-Piedicolle areas.

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(landslides, liquefaction, surface faulting and fracturing); definition of the subsoil model for the numerical simulation;

Task 4: geophysical characterization of the seismically homogeneous microzones. Above all MASW and microtremor investigations will be used to evaluate the Vs vs. depth profile;

Task 5: seismic monitoring and microtremor recordings;Task 6: 1D and 2D numerical simulations;Task 7: elaboration of the seismically homogeneous microzones map characterized by the

amplification factors obtained from the 1D and 2D numerical simulation.Considering that the geological setting of Santa Lucia is placed in a ridge characterized

by outcropping of arenaceous-pelitic lithotypes as bedrock, we will analyse its seismic site response also through 2D numerical simulation to estimate the possible contribution of the topographic effect.

Conclusions. As regards the Seismic Microzonation (Level 3) of Santa Lucia and Capitignano the main topics to be explored will be:

i) for Santa Lucia, the influence of fracture/fault network and the weathering cover of thefor Santa Lucia, the influence of fracture/fault network and the weathering cover of the terrigenous bedrock and the topographic effect on the seismic site response;

ii) for Capitignano, the influence of the bedrock morphology and the seismostratigraphyfor Capitignano, the influence of the bedrock morphology and the seismostratigraphy of the Quaternary deposits on the seismic site response and the liquefaction hazard evaluation and the mapping of the fault zones and fault setbacks of the presumed active Capitignano fault;

iii) in both the areas we will investigate the Seismic Hazard evaluation of the earthquakein both the areas we will investigate the Seismic Hazard evaluation of the earthquake prone landslides and the seismostratigraphy characterization through specific geophysical investigations (above all microtremor recordings and MASW).

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