Local seismic response studies in the north-western portion of the August 24th, 2016 Mw 6.0 earthquake affected area. The case of Visso village (Central Apennines).

In this work, we investigate the possible causes of the differential damaging observed in Visso village (Central Apennines, about 28 km north from the August 24th, 2016 Mw 6.0 earthquake epicenter). Following insights from the available geological cartography at 1:10.000 scale, a preliminary geophysical survey has been performed in the damaged area in order to constrain geometries and extent of the subsoil lithotypes. Then, these results have been used to retrieve a Vs profile close to the most heavily damaged buildings. This latter has been used as input for a numerical analysis aimed at deriving the motion at the ground level in the study area. In particular, a linear equivalent simulation has been performed by means of EERA code and the waveform has been obtained convolving the time history recorded during the August 24th, 2016 mainshock at Spoleto Monteluco (SPM) site. Our preliminary results indicate a possible correlation of damaging to the thickness and shape of the geological units. Nevertheless, further analyses are necessary to highlight any 2D basin and / non- linear soil behaviour effects in order to compare them to the intrinsic buildings vulnerability, according to the EMS98 guidelines

New stratigraphic constraints for the Quaternary source-to-sink history of the Amatrice Basin (central Apennines, Italy)

New stratigraphic constraints have been detailed for the Amatrice Basin, an intermountain morpho-structural depression of the central Apennines (Italy) hosting up to 60-m-thick Quaternary continental deposits. Through the results coming from a 1:5,000 scale field survey and from facies analyses, we documented the geometry, thickness, and extent of the post-orogenic continental deposits filling this basin. The Quaternary deposits form a complex architecture of purely aggradational and aggradational/degradational terraces with a dominant component of conglomerates and gravels, at the bottom, and subordinate sands, at the top. The Quaternary deposits overlie an up to 1-km-thick succession of flysch sediments that accumulated in the western Laga Basin during the Miocene syn-orogenic phases in central Apennines. The collected data are used to constrain the style and mechanisms of both syn-orogenic (i.e., subsidence and terrigenous sedimentation in foredeep environment) and post-orogenic (i.e., uplift, erosion, and continental sedimentation) phases documented for the central Apennines. In particular, the post-orogenic history of the Amatrice Basin, if compared with those of surrounding intermountain basins of the central Apennines, includes limited basin subsidence, reduced thickness of the post-orogenic covers and progressive deepening of the drainage network during the Quaternary. The results shed light on the source-to-sink history of the Amatrice Basin, which results from a long-lived interaction between regional-scale factors (climate changes, chain uplift, and extensional tectonic regime) that influenced the activity of the hydrodynamic pattern and the amount of intrabasinal sedimentation during the Quaternary

Domains of seismic noise response in faulted limestone (central Apennines, Italy): insights into fault-related site effects and seismic hazard

Studying seismic response at complex geological settings is a challenge due the occurrence of site effects related to widespread faulting/fracturing characteristics of the rock masses. Fault-related site effect is always a crucial aspect of an assessment of seismic hazard, but especially in assessments of areas where urban settlements are located in the proximity of regional fault zones. In order to detail the correlation between fault properties and seismic noise response (in terms of directional amplification), we have used a multidisciplinary approach to study a pervasively faulted limestone sequence cropping out in the central Apennines (Italy). We integrated results from (1) geological and structural surveys, (2) in situ geomechanical analyses and (3) geophysical measurements (ambient noise measurements processed with the H/V technique) performed along and across a 50 m-thick, NW\u2013SE-striking fault zone cutting through a limestone sequence. We then reconstructed the architecture of the fault zone by individualising different structural domains (a fault core and two damage zones) and, eventually, we evaluated the fracture intensity across the fault zone by correlating structural (discontinuity spacing, discontinuity pervasivity, size of lithons) and geomechanical (rebound hardness index provided by the Schmidt hammer) parameters. Ambient noise measurements documented a variability of directional amplification across the fault zone and in the surrounding undeformed rock mass, making it possible to recognise possible site effects. The results show the occurrence of a main NE\u2013SW-trending directional amplification oriented perpendicular to the strike of dominant slip structures within the fault core, whereas minor polarisation trends are transversal-to-perpendicular to the strike of subsidiary structures within the damage zones. The results support evidence of structurally-controlled directional amplification due to the stiffness anisotropy produced by the orientation of fault-related structures. When compared with results from published studies, our dataset can be used for understanding factors (i.e. the meso-scale fault properties) leading to directional amplification within a fault zone. Accordingly, we discuss our results in terms of the seismic response of the fault zones and the mitigation of seismic hazard in areas associated to tectonic activity

Domains of seismic noise response in faulted limestone (central Apennines, Italy). Insights into fault-related site effects and seismic hazard

Studying seismic response at complex geological settings is a challenge due the occurrence of site effects related to widespread faulting/fracturing characteristics of the rock masses. Fault-related site effect is always a crucial aspect of an assessment of seismic hazard, but especially in assessments of areas where urban settlements are located in the proximity of regional fault zones. In order to detail the correlation between fault properties and seismic noise response (in terms of directional amplification), we have used a multidisciplinary approach to study a pervasively faulted limestone sequence cropping out in the central Apennines (Italy). We integrated results from (1) geological and structural surveys, (2) in situ geomechanical analyses and (3) geophysical measurements (ambient noise measurements processed with the H/V technique) performed along and across a 50 m-thick, NW–SE-striking fault zone cutting through a limestone sequence. We then reconstructed the architecture of the fault zone by individualising different structural domains (a fault core and two damage zones) and, eventually, we evaluated the fracture intensity across the fault zone by correlating structural (discontinuity spacing, discontinuity pervasivity, size of lithons) and geomechanical (rebound hardness index provided by the Schmidt hammer) parameters. Ambient noise measurements documented a variability of directional amplification across the fault zone and in the surrounding undeformed rock mass, making it possible to recognise possible site effects. The results show the occurrence of a main NE–SW-trending directional amplification oriented perpendicular to the strike of dominant slip structures within the fault core, whereas minor polarisation trends are transversal-to-perpendicular to the strike of subsidiary structures within the damage zones. The results support evidence of structurally-controlled directional amplification due to the stiffness anisotropy produced by the orientation of fault-related structures. When compared with results from published studies, our dataset can be used for understanding factors (i.e. the meso-scale fault properties) leading to directional amplification within a fault zone. Accordingly, we discuss our results in terms of the seismic response of the fault zones and the mitigation of seismic hazard in areas associated to tectonic activity

New stratigraphic constraints for the Quaternary source-to-sink history of the Amatrice Basin (central Apennines, Italy)

New stratigraphic constraints have been detailed for the Amatrice Basin, an intermountain morpho-structural depression of the central Apennines (Italy) hosting up to 60-m-thick Quaternary continental deposits. Through the results coming from a 1:5,000 scale field survey and from facies analyses, we documented the geometry, thickness, and extent of the post-orogenic continental deposits filling this basin. The Quaternary deposits form a complex architecture of purely aggradational and aggradational/degradational terraces with a dominant component of conglomerates and gravels, at the bottom, and subordinate sands, at the top. The Quaternary deposits overlie an up to 1-km-thick succession of flysch sediments that accumulated in the western Laga Basin during the Miocene syn-orogenic phases in central Apennines. The collected data are used to constrain the style and mechanisms of both syn-orogenic (i.e., subsidence and terrigenous sedimentation in foredeep environment) and post-orogenic (i.e., uplift, erosion, and continental sedimentation) phases documented for the central Apennines. In particular, the post-orogenic history of the Amatrice Basin, if compared with those of surrounding intermountain basins of the central Apennines, includes limited basin subsidence, reduced thickness of the post-orogenic covers and progressive deepening of the drainage network during the Quaternary. The results shed light on the source-to-sink history of the Amatrice Basin, which results from a long-lived interaction between regional-scale factors (climate changes, chain uplift, and extensional tectonic regime) that influenced the activity of the hydrodynamic pattern and the amount of intrabasinal sedimentation during the Quaternary

Local seismic hazard assessment in explosive volcanic settings by 3D numerical analyses.

In this study, we face the problem of local seismic response in explosive volcanic setting by using an integrated geological-geophysical-geotechnical approach in the test area of Stracciacappa maar (Sabatini Volcanic District, central Italy). Our aim is to understand if the horizontal and vertical chaotic heterogeneity typical of the volcanic deposits influence site response. The Stracciacappa maar is an active eruptive centre characterised by a crater of about 1 km in diameter and a crater floor of about 30-40 m below the rim (De Rita et al. 1983; Sottili et al. 2012). The ring is mainly composed by the pyroclastic succession belonging to the last phreatomagmatic activity. This pyroclastic succession generally bends outward the rim with low angle dip (10-20°). It consists of at least 25 metres thick alternation of decimetre- to centimetre-thick layers of fine-medium ash and small lapilli. The crater depression is filled by epiclastic debris deposits and by recent and present-day lacustrine muds. The epiclastic debris deposits, of alluvial and delta origin, consist of alternation of cm-thick reworked fine-grained and coarse-grained volcaniclastic material, dipping with low-angle (1s) motions, compared to tectonic events of equivalent magnitude (Jousset and Douglas 2007); the unscaled recording at Bronte Station (BNT in ITACA database, http://itaca.mi.ingv.it) of the ML=4.4 October 27, 2002 event was employed; 2) a high magnitude far-field “tectonic” event (tectonic scenario), whose reference spectrum was built with Ground Motion Prediction Equations (Ambraseys et al., 2005) assuming M=6.5 and distance of 70 km. These conditions are compatible with seismogenic sources located in central Apennines of Italy. Three unscaled recordings of events characterised by magnitude and distance in the range of 6-7 and 60-90 km, respectively, were extracted from ITACA database (http://itaca.mi.ingv.it), matching on average the reference spectrum Two subsoil models have been considered: a detailed model (based on distribution of the lithotypes unravelled by the geological survey) and a simplified one (obtained by grouping interfingering lithotypes resting below the lacustrine silty clays). The result show that the two models have similar response in all range of the interesting period (0.1-1.0s); the damping properties of soft clays and sands deposits in the upper meters reduce the difference in the seismic response at the surface of both models. The results suggest the possibility to simplify the heterogeneous distribution of deposits in this volcanic context for assessment of seismic response purposes. Finally, we carried out both linear and equivalent linear analyses in one-dimensional and bi-dimensional conditions, in order to investigate the bidimensional effects and the role of nonlinearity on the seismic response,. In linear case the behaviour of soils was assumed linear visco-elastic with small strain damping ratio values D0; amplification factors higher than 10 were reached at 2 Hz at soft clays surface in correspondence of the centre and western edge of the maar in bi-dimensional analysis, whereas the 2D/1D ratios were in the order of 2-3 around 2 Hz with maximum values at the maar edges. In the nonlinear analyses, the maximum amplifications dropped below 10 and the 2D effects (i.e., 2D/1D ratios) were generally lower than 2 in the whole range of frequency

Geology of the central part of the Amatrice Basin (Central Apennines, Italy)

A 1:5,000 scale geological map and 31 geological cross-sections are presented for the surroundings of Amatrice village (central Apennines, Italy), epicentral area of the first damaging earthquake of the 2016–2017 seismic sequence. This detailed geological dataset focuses on: (i) the extent, the thickness, and the internal stratigraphic architecture of the Quaternary continental deposits; (ii) the bedding and the thickness of the Miocene substratum; and (iii) the spatial distribution of the main fault systems. The provided dataset would update the available regional geological maps in deciphering the syn-to-post-orogenic history of the Amatrice Basin. Eventually, the accuracy of the geological mapping would represent a basic tool for interpreting and integrating the multidisciplinary dataset deriving from post-seismic activities