Geophysical and geochemical methods were applied to detect the subsurface setting of an Upper Pleistocene-Holocene fluvial incised-valley where a travertine body intercalates between alluvial ...deposits of the Tiber river (central Italy), at Prima Porta (close to Rome). This study allowed us to provide more information regarding the local stratigraphic architecture and structural features, as a reference analogue to similar settings: i.e., hard (stiff) lithic travertines buried below fine and loose alluvial plain covers. Two Electrical Resistivity Tomography (ERT) profiles, interpreted and calibrated using previously collected litho-stratigraphic data from a borehole, identified a massive body, with a relatively high resistivity that correlates with the travertine deposit of Prima Porta. In addition to ERT, ambient noise measurements, processed with the HVSR technique and 2D array, and seismic refraction tomography were carried out; HVSR data were highly consistent with ERT results and allowed to discriminate between the travertine body and the silty-sand channels and overbank deposits, which were attributed to the Tiber river’s evolution during Upper Pleistocene-Holocene. Finally, the presence of cracks/fractures could be inferred, as suggested by slight polarisation effects recorded in the HVSR results and soil-gas anomalies.
Archaeological areas in the mountain region of central Italy can be seriously threatened by geological hazards, and efforts are required to preserve cultural heritage. The Lucus Angitiae is a ...pre-Roman site located along the western edge of the Fucino Basin, the largest continental depression of central Apennines. The carbonate slope overhanging the area is affected by active rockfall processes from two main rock escarpments. In this paper, rockfall assessment was pursued through a 3D kinematic modelling, performed by adopting a probabilistic approach. Specific attention was dedicated to the choice and calibration of the input data, based on field evidence and a literature review. Two different sizes of wedge-shaped rock blocks were identified on rock escarpments, and specific stability analyses were performed. Sensitivity analyses accounting for possible triggering factors, such as water pressure increase and seismic action, were also carried out, together with an investigation of the seismological characteristics of the area. The results of the numerical simulations were used to design effective countermeasures in the framework of a mitigation plan for protection of the archaeological site. Finally, clues of gravity-driven slope deformations at the slope scale were documented, framing the rockfall process in a wider geological scenario.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Numerical simulations of seismic site response require the characterization of the nonlinear behaviour of shallow subsoil. When extensive evaluations are of concern, as in the case of seismic ...microzonation studies, funding problems prevent from the systematic use of laboratory tests to provide detailed evaluations. For this purpose, 485 shear modulus reduction, G\G0(γ) and damping ratio, D(γ) curves were collected from multiple literature sources available in Italy. Each curve was associated with the related engineering geological units considered in seismic microzonation studies. A statistical analysis of the data was carried out with the aim of shedding light on the significant difference between the laboratory classification of samples and the macroscopic/engineering geological one, provided during seismic microzonation studies. Since the engineering geological classification plays a prominent role in extensive site response evaluations, the outcomes of the present work may be of help at least when preliminary seismic response estimates are of concern. The dataset provides reference information that can serve as key data for large-scale hazard assessments worldwide.
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.
The refraction reprocessing of the CROP11-1999 seismic reflection data, which were acquired for deep seismic exploration using a split-spread long offset geometry, provides valuable new insights into ...the main geological structures of the central Apennines. In this study, we present the geophysical interpretation of a sub-transect of the CROP11 seismic profile, crossing the Piani Palentini and Fucino basins carried out using an integrated approach based on the refraction tomography, the stacked refraction convolution section, and the seismic reflection. The reprocessing allowed us to obtain, for the first time, a high resolution (about 15 m in distance and depth) P-waves seismic velocity 2D model and the imaging of the refractor interface of the basin up to the depth of the Meso-Cenozoic carbonate substratum. The outcomes, combined with the interpretation of a CROP11 seismic reflection sub-transect and a subparallel commercial seismic reflection profile, allowed us to highlight a complex basin-fill architecture and stratigraphy. Four seismo-facies, characterized by different Vp velocity values, were recognized above the Meso-Cenozoic carbonate substratum. In particular, a low-velocity zone (LVZ) was evidenced in both basins. The geophysical interpretation and the comparison with the outcropping sequences allowed us to associate it with an upper Messinian thrust-top deposit.
The obtained model constitutes an essential geophysical-geological informative base for future investigations on seismic wave propagation and site response studies at the large scale of the Fucino Basin, one of the areas of the Italian territory with a high seismic hazard.
•Reprocessing and repurposing old seismic data with new technologies.•High-resolution on first arrivals tomography sand refractor imaging.•High-resolution on Vp model useful for seismic response estimate at basin scale.•2D seismo-stratigraphic analysis.•Evidence of Miocene synorogenic deposits underneath the Plio-Quaternary basin-fill.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper we present a new methodological approach which integrates geological and geophysical data into a 3D modelling process to be mainly employed in seismic hazard assessment studies of ...earthquake-prone areas around the world, as well as in applications for land use and urban planning. As a case study, the reconstruction of a geology-based 3D velocity model of the uppermost hundreds of metres of the Amatrice high-seismic-hazard area is described.
The model was constructed using geological (e.g., maps, cross-sections and core-wells) and geophysical (e.g., down-hole, MASW, refraction, and seismic noise measurements) data, which were georeferenced and uploaded into 3D geological modelling software, where faults, stratigraphic boundaries, and geophysical attributes were digitised, checked, hierarchised, and modelled. The performed 3D geological model was parameterised with Vs and Vp velocities and, finally, the environmental noise (i.e., horizontal-to-vertical spectral ratio analysis, HVSR) recorded at some seismic stations was compared with the seismic responses modelled at some nearby control points.
In the study area, the proposed geology-based 3D velocity model represents both a new potential geophysical prediction tool for areas devoid of geophysical measurements (i.e. HVSR curves) and a potential input-model for future ground-motion and seismic-wave-propagation simulations aimed at a more precise local seismic response assessment and, consequently, at the development of more realistic seismic hazard scenarios.
The model here presented constitutes a first version of the 3D geological-geophysical model for the studied area, which will be improved with new data and more advanced algorithms available in the future.
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•A new methodological approach for the 3D geophysical model reconstructing is proposed.•The first 3D geology-based velocity model of the Amatrice area was reconstructed.•The model integrates and completes the earlier studies on the Amatrice Basin.•The performed model represents a new geophysical prediction tool for the Amatrice area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work presents results obtained from numerical site response analyses in the area of Amatrice (central Italy) with a main focus on the town's historical centre, where a more significant ...differential damage was observed after the August 24th, 2016, Mw 6.0 earthquake and the following aftershocks. Geological field investigations were performed and used to define a series of detailed geological cross-sections across the hill, which is the distinctive morphological feature of the town. Following insights from geological cartography, four continuous coring boreholes were drilled to obtain a new refined subsoil model of the area at depth; three of these boreholes were used to perform down-hole tests to constrain the shear-wave velocity (Vs) of the geological units. The subsoil model also included the results of the available seismic arrays and 80 single station ambient vibration stations, which allowed the calibration of the dynamic model, enhancing its robustness. The analyses allowed for a comparison of available empirical amplification functions and the simulated transfer functions of this study. Empirical transfer functions are represented in this case through the available Standard Spectral Ratio curves computed from recorded earthquakes of the 2016–2017 seismic sequence. They show a broad peak centred between 2 and 3 Hz, corresponding to the predominant frequencies of the hill, and a flat response outside the hill, in good agreement with the modelled transfer functions determined following two-dimensional (2D) approach. Conversely, one-dimensional (1D) transfer functions could not describe the amplification in the same range, confirming the evidence of overlapping topographic and stratigraphic effects. In the historical part of the town, only ambient vibration data were available. Notwithstanding that only a comparison of numerical resonance frequencies with the experimental frequencies highlighted using the horizontal-to-vertical spectral ratio (HVSR) method on ambient vibration data is possible in this case, reasonable agreements were found in the considered frequency range 1–10 Hz. In-depth characterisation of the subsoil of the historical centre of Amatrice provided a useful tool for challenging the problem of the realistic ground motion estimates, by evaluating possible local effects which could enhance or modify the input motion.
•A significant two-dimensional effect is recognisable on the eastern side of the Amatrice historical centre.•Site effects play a role on damage patterns in complex geological and morphological sites.•Main features of the Amatrice subsoil model have a relevant value at a regional scale, involving the wider epicentral area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Downtown L'Aquila suffered severe damage (VIII-IX EMS98 intensity) during the 2009 April 6 M
w 6.3 earthquake. The city is settled on a top flat hill, with a shear-wave velocity profile characterized ...by a reversal of velocity at a depth of the order of 50–100 m, corresponding to the contact between calcareous breccia and lacustrine deposits. In the southern sector of downtown, a thin unit of superficial red soils causes a further shallow impedance contrast that may have influenced the damage distribution during the 2009 earthquake.
In this paper, the main features of ambient seismic vibrations have been studied in the entire city centre by using array measurements. We deployed six 2-D arrays of seismic stations and 1-D array of vertical geophones. The 2-D arrays recorded ambient noise, whereas the 1-D array recorded signals produced by active sources. Surface-wave dispersion curves have been measured by array methods and have been inverted through a neighbourhood algorithm, jointly with the H/V ambient noise spectral ratios related to Rayleigh waves ellipticity. We obtained shear-wave velocity (Vs) profiles representative of the southern and northern sectors of downtown L'Aquila.
The theoretical 1-D transfer functions for the estimated Vs profiles have been compared to the available empirical transfer functions computed from aftershock data analysis, revealing a general good agreement. Then, the Vs profiles have been used as input for a deconvolution analysis aimed at deriving the ground motion at bedrock level. The deconvolution has been performed by means of EERA and STRATA codes, two tools commonly employed in the geotechnical engineering community to perform equivalent-linear site response studies. The waveform at the bedrock level has been obtained deconvolving the 2009 main shock recorded at a strong motion station installed in downtown. Finally, this deconvolved waveform has been used as seismic input for evaluating synthetic time-histories in a strong-motion target site located in the middle Aterno river valley. As a target site, we selected the strong-motion station of AQV 5 km away from downtown L'Aquila. For this site, the record of the 2009 L'Aquila main shock is available and its surface stratigraphy is adequately known making possible to propagate the deconvolved bedrock motion back to the surface, and to compare recorded and synthetic waveforms.
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