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Estimation of amplification factors (AFs) at the local or regional scale is an important task in land planning and seismic design, especially in areas with high seismic hazards and complex geological and geomorphological structures of the territory, such as Italy. When multiple seismic recordings at a single site are available, they can be exploited to estimate AFs empirically through many methods, such as: a) spectral ratios between i) the horizontal and vertical ground-motion components and ii) the shaking observed at the site and at a reference rock site, both for acceleration response and Fourier spectra; b) parametric or non-parametric generalized spectral inversion techniques; and c) decomposition of residuals of a nonergodic Ground Motion Model (Rodriguez-Marek et al., 2011; Priolo et al., 2020, among the others) to estimate repeatable within-site terms (δS2S). In this study, we exploited the estimates of δS2S provided by Lanzano et al (2022), through the ITACA (ITalian ACcelerometric Archive) web portal (https://itaca.mi.ingv.it/ItacaNet_32/#/products/itacas2s_flatfile), to compute the AFs for about 800 recording sites in Italy. We then compare AFs estimates with different proxies for predicting the site effects, such as Vs profile, resonance frequency, cover geology and topographic slope. Moreover, we also employed the empirical AFs to validate the estimates provided by 1D, 2D and 3D numerical modeling of the site response. Later, we investigate spatial correlation of the AFs in urban areas, where dense networks are installed., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

In this paper, we present the work carried out to characterize the spatial variability of seismic site response related to local soil conditions in the city of Milan and its surroundings, an area with ∼3 million inhabitants and a high density of industrial facilities. The area is located at the northwestern end of the Po Plain, a large and deep sedimentary basin in northern Italy. An urban-scale seismo-stratigraphic model is developed based on new passive and active seismic data, supported by the available geological data and stratigraphic information from shallow and deep vertical wells. In particular, 33 single-station and 4 ambient-vibration array measurements are acquired, together with 4 active multichannel analyses of surface waves (MAWS). To estimate the resonant frequencies of the sediments, the horizontal to vertical spectral ratio technique (HVSR) is applied to the ambient-vibration recordings, whereas to determine the Rayleigh-wave dispersion curves from the passive array, the data are analysed using the conventional frequency-wavenumber, the modified spatial autocorrelation and the extended spatial autocorrelation (ESAC) techniques. The array data are used to determine the local shear wave velocity profiles, VS, via joint inversion of the Rayleigh-wave dispersion and ellipticity curves deduced from the HVSR. The results from HVSR show three main bands of amplified frequencies, the first in the range 0.17–0.23 Hz, the second from 0.45 to 0.65 Hz and the third from 3 to 8 Hz. A decreasing trend of the main peaks is observed from the northern to the southern part of the city, allowing us to hypothesize a progressive deepening of the relative regional chrono-stratigraphic unconformities. The passive ambient noise array and MASW highlight the dispersion of the fundamental mode of the Rayleigh-wave in the range 0.4–30 Hz, enabling to obtain detailed Vs. profiles with depth down to about 1.8 km. The seismo-stratigraphic model is used as input for 1D numerical modelling assuming linear soil conditions. The theoretical 1D transfer functions are compared to the HVSR curves evaluated from both ambient noise signals and earthquake waveforms recorded by the IV. MILN station in the last 10 years.

We describe the main structure and outcomes of the new probabilistic seismic hazard model for Italy, MPS19 [Modello di Pericolosità Sismica, 2019]. Besides to outline the probabilistic framework adopted, the multitude of new data that have been made available after the preparation of the previous MPS04, and the set of earthquake rate and ground motion models used, we give particular emphasis to the main novelties of the modeling and the MPS19 outcomes. Specifically, we (i) introduce a novel approach to estimate and to visualize the epistemic uncertainty over the whole country; (ii) assign weights to each model components (earthquake rate and ground motion models) according to a quantitative testing phase and structured experts’ elicitation sessions; (iii) test (retrospectively) the MPS19 outcomes with the horizontal peak ground acceleration observed in the last decades, and the macroseismic intensities of the last centuries; (iv) introduce a pioneering approach to build MPS19_cluster, which accounts for the effect of earthquakes that have been removed by declustering. Finally, to make the interpretation of MPS19 outcomes easier for a wide range of possible stakeholders, we represent the final result also in terms of probability to exceed 0.15 g in 50 years., peer-reviewed

The availability of high-quality waveforms recorded in epicentral areas of moderate-to-strong earthquakes is a key factor for investigating ground-motion characteristics close to the seismic source. In this study, near-source strong-motion waveforms (named NESS1) were collected from worldwide public archives with the aim of building a flat file of high-quality metadata and intensity measures (IMs) of engineering interest. Particular attention was paid to the retrieval of reliable information about event sources, such as geometries and rupture mechanisms that are necessary to model near-source effects for engineering seismology and earthquake engineering applications. The accelerometric records are manually and uniformly processed, and the associated information is fully traceable. NESS1 consists of about 800 three-component waveforms relative to 700 accelerometric stations, caused by 74 events with moment magnitude larger than 5.5 and hypocentral depth shallower than 40 km, with Joyner-Boore distance up to 140 km. Ground-motion data were selected to have a maximum source-to-site distance within one fault length, defined through seismological scaling relations. About 40 records exhibit peak acceleration or peak velocity exceeding 1g or 120 cm=s, and they represent some of the largest ground motion ever recorded. Evidence of near-source effects was recognized in the NESS1 dataset, such as velocity pulses, large vertical ground motions, directional and hanging-wall amplifications and fling step. In particular, around 30% of the records was found to exhibit pulse-like characteristics that are possibly due to forward rupture directivity. Electronic Supplement: Table listing the main features of the selected events, including the references of fault geometry parameters and Figures showing further metadata and intensity measures distributions of the NESS1 flat file.

During the Mw 6.0 Amatrice earthquake, which struck Central Italy on the 24th August 2016, the accelerometric station IT.AMT, located at about 10km from the epicentre recorded the highest values of the ground motion (Peak Ground Acceleration of the east component reached 0.87 g). Was IT.AMT station affected also by local soil conditions? To understand the role played by the site effects in the ground motion observed at AMT, we performed a detailed geological - geotechnical characterization of the site. Then, numerical analyses of seismic site response were carried out using 2D approaches. In parallel, several analysis were also performed on seismic records, to infer empirical amplification functions, used to compare the results of the numerical simulations. This study was partially supported by the Italian Department of Civil Protection (DPC) of the Presidency of Council of Ministers. The INGV-CNR IGAG collaboration made possible the realization of this multidisciplinary study, which includes detailed seismological, geological and geophysical analyses.

This work presents the results from numerical analyses in the damaged area of Saletta hamlet (Amatrice municipality), aiming at discussing factors leading to the observed damages after the 24th August 2016 Mw 6.0 earthquake and the following aftershocks. The area of Saletta was in fact highly ravaged by the first earthquake and during the whole seismic sequence. Geological-technical detailed field investigations were combined with an Electrical Resistivity Tomography and several noise measurements for better evaluating the main geological-morphological variability over the study area. Following insights from the reconstructed geological setting, a continuous coring borehole was drilled and a down-hole test performed together with a passive 2D small array and an active 1D MASW measurement. All these data were used to obtain the subsoil model for the numerical analyses that were carried out using both 1D and 2D approaches, including linear and equivalent linear ones, aiming at evaluating site effects.

ShakeMap is the tool to evaluate the ground motion effect of earthquakes in vast areas. It is useful to delimit the zones where the shaking is expected to have been most significant, for civil defense rapid response. From the earthquake engineering point of view, it can be used to infer the seismic actions on the built environment to calibrate vulnerability models or to define the reconstruction policies based on observed damage vs shaking. In the case of long-lasting seismic sequences, it can be useful to develop ShakeMap envelopes, that is, maps of the largest ground intensity among those from the ShakeMap of (selected) events of a seismic sequence, to delimit areas where the effects of the whole sequence have been of structural engineering relevance. This study introduces ShakeMap envelopes and discusses them for the central Italy 2016–2017 seismic sequence. The specific goals of the study are: (i) to compare the envelopes and the ShakeMap of the main events of the sequence to make the case for sequence-based maps; (ii) to quantify the exceedance of design seismic actions based on the envelopes; (iii) to make envelopes available for further studies and the reconstruction planning; (iv) to gather insights on the (repeated) exceedance of design seismic actions at some sites. Results, which include considerations of uncertainty in ShakeMap, show that the sequence caused exceedance of design hazard in thousands of square kilometers. The most relevant effects of the sequence are, as expected, due to the mainshock, yet seismic actions larger than those enforced by the code for structural design are found also around the epicenters of the smaller magnitude events. At some locations, the succession of ground-shaking that has excited structures, provides insights on structural damage accumulation that has likely taken place; something that is not accounted for explicitly in modern seismic design. The envelopes developed are available as supplemental material.