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After a strong earthquake, the rapid identification of the extent of the affected area is the most crucial task of civil protection authorities. The information provided by those directly affected by an event makes the difference since it offers the opportunity to take advantage of direct observations and, in the case alert systems are available, to verify if they worked properly. Thanks to the fruitful collaboration between the Regional Civil Protection of Friuli Venezia Giulia and the National Institute of Oceanography and Applied Geophysics – OGS in Italy, a procedure for collecting rapid information about the impact of an earthquake using an expert crowdsourcing approach has been in place for some years. The volunteers of the civil protection, appropriately trained, upon receipt of the seismic event notification, are asked to rapidly compile a specific questionnaire, describing the impact of the event. Data are rapidly coded, and the results are summarized in a seismic impact map showing the effect of the earthquake throughout the territory in a simplified way. This map complements the impact estimation provided by the analysis of recorded shaking data. This paper describes the results obtained by analyzing the “Trained Volunteers Seismic Evaluation” questionnaire (TVSE) completed by volunteers for some of the most significant events in recent years.

The comparison of seismic‐hazard maps produced in different countries, or computed for the same country but at different times, is often hampered by the difficulties encountered in properly accounting for the differences among the implemented methodologies. An example of such difficulty is given by the comparison between the hazard maps computed during the Cold War period for the former Soviet Union, which includes vast regions exposed to high seismic hazard (e.g., the central Asian countries and the Caucasus region), and recent assessments carried out for the same regions following approaches developed in Western countries (e.g., Ullah et al. , 2015). These comparisons should take into account the differences in the underlying methodologies used in the former Soviet Union and, in several cases, still in use. In the Western countries, the process of formalizing the seismic‐hazard assessment within a probabilistic framework (probabilistic seismic‐hazard assessment [PSHA]) was developed during the 1960s at the Universidad Nacional Autonoma de Mexico (UNAM) and at the Massachusetts Institute of Technology (MIT) (Rosenblueth, 1964; Esteva, 1967, 1968, 1970; Cornell, 1968). With the works of Cornell (1971) and Merz and Cornell (1973), PSHA was finally formalized within the context of the total probability theorem, which accounted for ground‐motion variability, and its use then became widespread through the implementation and dissemination of the EQRISK software (McGuire, 1976). A comprehensive review of the early development of PSHA can be found in Bommer and Abrahamson (2006) and in McGuire (2008). On the other hand, the development of a probabilistic framework for seismic‐hazard assessment in the former Soviet Union (hereinafter referred to as the USSR [Union of Soviet Socialist Republics]) was initiated in the 1940s with the works of Medvedev (1947) and developed by Riznichenko in the 1960s (e.g., Riznichenko, 1965, 1992). To quantitatively represent the …

Over the last decade, increasing attention has been paid by the international community to the topic of earthquake early warning (EEW) systems, as a viable solution to protect specific hazard‐prone targets (major cities or critical infrastructure) against harmful seismic events. The aim of the EEW system is to detect the occurrence of an earthquake and to determine its relevant characteristics (such as location and magnitude) early enough to predict the ground shaking at the target site before the S ‐wave arrival. Possible emergency protocols that can be activated upon event detection range from slowing down or stopping rail traffic (Nakamura, 2004; Horiuchi et al. , 2005; Espinosa‐Aranda et al. , 2011), safely shutting down or activating protective measure of critical infrastructures such as nuclear power plants (Saita et al. , 2008), to broadcasting alerts to the general public (Wenzel and Lungu, 2000; Lee and Espinosa‐Aranda, 2002; Allen and Kanamori, 2003; Horiuchi et al. , 2005; Wu et al. , 2007). Only few systems have been actually implemented and are currently operational. Examples of regional applications are the systems operating in California, Japan, and Taiwan, whereas targeted systems have been developed, for instance, in Mexico, Irpinia (Italy), and Vrancea (Romania). We refer the interested readers to the comprehensive references in Wenzel and Zschau (2014). Despite the potential benefits of EEW system, several factors so far hindered their widespread application especially in economically developing countries. When the distance between the seismic sources and the exposed target is too short for instance, or there is no technological infrastructure supporting real‐time, automatic operations, the information provided by the EEW system cannot be exploited for pre‐event actions. In these cases, which occur remarkably often in many seismic regions, the level of ground shaking predicted by the system can still be used as input …

SUMMARY The estimation of shear wave velocity and attenuation in near-surface geology is of primary importance in engineering seismology. In fact, such knowledge is essential for site response studies when preparing improved seismic hazard scenarios. In this study, we propose a linear inversion of the spectra of a deconvolved wavefield collected by a borehole array in Istanbul, Turkey. The spectra are calculated using as a reference the recordings collected by a sensor at the surface. This allows us to minimize the effect of the deconvolution filter on the peaks’ amplitudes. The feasibility of the proposed inversion scheme and the parametrization of the velocity and attenuation models were tested and assessed using synthetic data. The real data inversion is carried out using observation from three weak motion events. Several starting models are used for each event, changing the values of the quality factor Qs, whereas the starting Vs profiles are fixed to what was obtained by the analysis of the deconvolved wavefield in the time domain. Our results showed that fairly well-constrained Vs models can be obtained while the variability of the Qs profile, both between different inversions of the same data set, and between the inversions of different data sets, might be large. This indicates that Qs variations observed in models derived by strong motion data inversions should be considered with care. However, the high agreement of the estimated soil profiles in the uppermost layer, both when using different events and different starting models, suggests that any variation in the S-wave velocity that might be estimated when using strong motion data should be reliable.

SUMMARY Inthisstudy,newintensitypredictionequationsarederivedforCentralAsia,consideringabout 6000 intensity data points from 66 earthquakes encompassing the surface-wave magnitude range of 4.6–8.3. The suitability of the functional form used for constructing the model is assessed by comparing its predictions with those achieved through a non-parametric model. The parametric regressions are performed considering different measures of the source-to-site distance, namely the hypocentral, epicentral and the extended distance metrics. The latter is defined as the minimum distance from the site to a line crossing the epicentres, oriented along the strike of the earthquake and having a length estimated from the event’s magnitude. Althoughtheextendeddistanceisintroducedasapreliminaryattempttoimprovetheprediction capability of the model by considering the finiteness of the fault extension, the standard deviation of the residual distribution obtained considering the extended distance (σ = 0.734) does not show an improvement with respect to the results for the epicentral distance (σ = 0.737). The similarity of the two models in term of average residuals is also confirmed by comparing the interevent errors obtained for the two regressions, obtaining very similar values for all earthquakes but the 1911, M 8.2 Kemin event. In particular, different evidences suggest that the magnitude of this event could be overestimated by about half a magnitude unit. Regarding the variability of the residual distribution, all the three considered components (i.e. interevent, interlocation and record-to-record variances) are not negligible, although the largest contribution is related to the record-to-record variability, suggesting that both source and propagation as well as site effects not captured by the considered model influence the spatial variability of the intensity values.

SUMMARY Temporary arrays installed in urban areas for investigating the upper-most geological structure typically comprised of a limited number of stations and are arranged in geometries constrained by environmental boundaries. Therefore, it is expected that the frequency–wavenumber images are significantly blurred by the array transfer function and are corrupted by noise. In this paper, the effect of the Richardson–Lucy regularization method applied to the problem of deblurring frequency–wavenumber images is investigated. The images are computed by analysing data from two small-aperture 2-D arrays, installed with different configurations in a test-site within the town of Potenza (Southern Italy) for near-surface investigations. We show that removing the effects of the array response from the frequency–wavenumber images improve the phase-velocity estimation, reducing the relevant level of uncertainty. Furthermore, the Richardson–Lucy regularization method is effective in reducing the level of noise related to spatial aliasing by eliminating spurious peaks, allowing the maxima related to different seismic sources to be better discriminated.

The rapid improvement in telemetry and computer technology is literally driving a revolution in earthquake engineering and, in particular, in the monitoring of civil built infrastructures. Monitoring buildings in earthquake-prone areas is a task of major importance both to ensure their structural integrity and to obtain an insight into their responses in the event of an earthquake in order to mitigate urban earthquake risk by new, effective seismic design provisions.

A method for deriving experimental dispersion curves of surface waves from active source recordings is presented. The method is based on the complex seismic trace analysis of surface waves (CASW) and is applicable when only two receivers are available. Reliable phase velocities are obtained when keeping the geophone interval smaller than one λ , allowing both a velocity structure as local as possible to be derived and to avoid long geophone spreads which are difficult to handle in urban areas. A large number of velocity estimates for each frequency can be estimated, even when using only two sensors, allowing statistical validation of the results, and providing a statistically defined uncertainty interval to be used in the dispersion curve inversion. The method is tested using synthetic seismograms and applied to real-world data, showing that it provides reliable estimates of apparent phase velocities. Although a final conclusion cannot yet be drawn, its application to observed data suggests it has the potential to be a useful method for distinguishing different modes.

The rapid characterization of ground motion during the initial stage of an earthquake is one of the most effective approaches for quantifying the hazard associated with its impact on populated or otherwise sensitive areas. Earthquake early warning (EEW) systems are based on this approach, and aim to mitigate earthquake hazard for a target area by the provision of timely warnings. In addition, during and soon after the occurrence of earthquakes, the necessity for information on the state of health of structures in real-time that permit timely warnings in case of damaging events requires structural health monitoring systems. The Self-Organising Seismic Early Warning Information Network (SOSEWIN) is a new concept in EEW and structural health monitoring (SHM) systems. SOSEWIN employs advances in various technologies to incorporate off-the-shelf sensor, processing and communications components into low-cost sensing units that are linked by advanced, robust and rapid communications routing and network organisational protocols that are appropriate for wireless mesh networks. Significant and innovative aspects of SOSEWIN are that each sensing unit performs on-site, independent analysis of the ground motion, and that the early warning is transmitted throughout the network by means of dedicated alarming processes. In this work, a description of the SOSEWIN philosophy, hardware, and software is provided, as well as an overview of its application within different contexts. In particular, we present the results of tests carried out with SOSEWIN in Istanbul, Turkey, where a first test-bed consisting of 20 instruments is installed, as well as a novel approach for EEW that exploits the SOSEWIN philosophy to obtain, in the event of an earthquake, a real-time structural response assessment following an interferometric approach (Fleming et al. 2009). Finally, the application of SOSEWIN for SHM purposes at a building in L’Aquila (Picozzi et al. 2009a), a suspension bridge in Istanbul (Picozzi et al. 2009b), and a historical arch bridge in Luxembourg City (Oth and Picozzi 2012) are presented.

The authors would like to thank Gusev (2016; hereafter referred to as Gu16) for his interest in our work (Bindi and Parolai, 2015; hereafter referred to as BP15) and for providing additional information about the methodology followed to prepare the hazard map for northern Eurasia included in the Global Seismic Hazard Assessment Program (GSHAP) model (Ulomov and the GSHAP region 7 Working Group, 1999, hereafter referred to as Ul99; Zhang et al. , 1999). The main interest of BP15 was to compare two probabilistic seismic‐hazard analysis approaches, namely the Riznichenko (1965) and the Cornell (1968, 1971) methods, which differ in the way they account for the aleatoric uncertainty. Although Gu16 agrees with the main conclusions of BP15 (“Another possible cause of the discussed discrepancy is certain difference between hazard calculation procedures of Riznichenko and Cornell. Both these observations of BP15 seem to be relevant, and need not be commented.”), he raises some criticisms against the discussions developed in BP15 regarding the GSHAP overestimation of the hazard level in central Asia (“Both assertments of BP15: that Ul99 hazard estimates are substantially exaggerated, and that this alleged fact is related to the use of Riznichenko (1965) procedures are incorrect.”). Here, it is worth remembering that, first, the overestimation of the Ul99 results is not an original statement of BP15, but, as also mentioned by Gu16, it was originally observed by Zhang et al. (1999) when compiling the GSHAP map, and, second, the Riznichenko approach followed in preparing the hazard map for northern Eurasia was a working hypothesis tested in BP15, not an absolute statement. Indeed, this hypothesis was inspired directly by Ul99 (“We calculate seismic hazard using an algorithm and software code designed by Gusev, Pavlov and Shumilina, following the principles of Riznichenko (1965) and Cornell (1968).”). Considering …

Earthquake early warning systems (EEWS) in their various forms are recognized as potentially valuable tools for mitigating against the risk associated with earthquakes (see Allen, 2013; Wenzel and Zschau, 2014). For example, operational systems currently exist in Japan (Horiuchi et al. , 2005; Kamigaichi et al. , 2009), Taiwan (Wu and Zhao, 2006; Wu, Chen, et al. , 2013), and Mexico (Espinosa‐Aranda et al. , 2009), while there are others nearing operational status, under development, or are being strongly considered in regions such as Italy (Satriano et al. , 2011), Turkey (Alcik et al. , 2009; Wenzel et al. , 2014), California (Bose et al. , 2009), Romania (Bose et al. , 2007), Israel (Allen et al. , 2012), and Spain (Carranza et al. , 2013). However, EEWS are not only valuable for the mainshock, but also for the period after a disastrous earthquake when there is the possibility of reducing losses due to aftershocks if early warning/rapid response systems can be rapidly deployed in the field. In such cases, the deployed instruments could serve a number of functions, such as 1. implementing a threshold‐based on‐site early warning system (OSEWS) for infrastructure; 2. monitoring the structural response, and its changes, of buildings and infrastructure in real time during the aftershock sequence; 3. allowing the assessment of the expected damage to nearby structures soon after an aftershock’s occurrence; 4. allowing the overall expected damage to a target structure during the aftershock sequence to be estimated; and 5. validating damage forecasts determined by probabilistic approaches (or others) and updating the fragility curves based on recorded ground motion. A recent important development in this direction is the Community Seismic Network approach and the Quake‐Catcher Network in California, U.S.A., based on the installation by community volunteers of low‐cost accelerometers in houses and buildings (Clayton et al. , 2011; Kohler et al. , 2013). Within the …

In this work, we investigate the site amplification effects observed in the Norcia plain, Central Italy. Data from 30 selected local earthquakes (2 ≤ Ml ≤ 4.1) recorded by a temporary seismic network composed by 15 stations, are analyzed to determine the spatial variability of site effects. Both the Horizontal-to-Vertical spectral ratio and the Standard Spectral Ratio techniques are applied to estimate the site amplification effects. The results show that most of the sites in the valley are affected by strong amplifications (up to a factor of 20) in the frequency range 0.5–5 Hz. The value of the fundamental frequency of resonance is strictly dependent on the location within the basin and on the sediment thickness. Strong amplifications also affect the vertical components. The time-frequency analysis performed on a station located inside the basin shows the presence of a large spectral amplitudes after the S-wave phase, not observed on a station located on the bedrock, suggesting the presence of locally generated wave trains. Then, in agreement with earlier observations for other alluvial basins in Central Italy, 2D–3D effects play an important role in determining the site amplification effects in Norcia.

After the recent Central Italy Earthquake of the 6th April 2009 (Mw = 6.3), the Italian and German engineer and geophysicist Task Force carried out a wide characterization of sites, buildings and damages. In Navelli, a town about 35 km far from epicentre, heavy damage occurred on a reinforced concrete (RC) building that represent an anomalous case of damage, when compared with those occurred in the neighbouring area. In this paper, characterization of the site and damage of the Navelli RC Building is reported and discussed. We performed ambient noise and strong motion measurements, installing one three-directional accelerometer on each floor of the structure and two in free-field, and we have carried out repeated measurements using a couple of three-directional tromometers. In the mean time, a geological survey was carried out and the site response was investigated, with the aid of down-hole measurements. It was thus possible to investigate the structural response and damage taking into account site condition. One of the main results of this work is that repeating analyses using ambient noise measurements show that the main structural frequencies reached after the first damaging shock are constant over time, and then the structural behaviour appears stationary at long term. On the other hand, the strong motion recordings show that the building exhibits a transient non-stationary behaviour as the fundamental frequency changes during each aftershock, then returning to the starting value after each event.

We exploit S-wave spectral amplitudes from 112 aftershocks (3.0 ≤ ML ≤ 5.3) of the L’Aquila 2009 seismic sequence recorded at 23 temporary stations in the epicentral area to estimate the source parameters of these events, the seismic attenuation characteristics and the site amplification effects at the recording sites. The spectral attenuation curves exhibit a very fast decay in the first few kilometers that could be attributed to the large attenuation of waves traveling trough the highly heterogeneous and fractured crust in the fault zone of the L’Aquila mainshock. The S-waves total attenuation in the first 30 km can be parameterized by a quality factor QS(f) = 23f 0.58 obtained by fixing the geometrical spreading to 1/R. The source spectra can be satisfactorily modeled using the omega-square model that provides stress drops between 0.3 and 60 MPa with a mean value of 3.3±2.8 MPa. The site responses show a large variability over the study area and significant amplification peaks are visible in the frequency range from 1 to more than 10 Hz. Finally, the vertical component of the motion is amplified at a number of sites where, as a consequence, the horizontal-to-vertical spectral ratios (HVSR) method fails in detecting the amplitude levels and in few cases the resonance frequencies.

The response of the soil-structure system near the Falkenhof Tower, Potsdam, Germany, has been monitored during the controlled explosion of a bomb dating to World War II. We installed eight 3-component velocimetric stations within the building and three in the surrounding area. We recorded several hours of seismic noise before and after the explosion, allowing the dynamic characterization of the structure both with ambient noise and forced vibration. We then compared the frequencies values and modal shapes of the structural modes evaluated both by analysing in the frequency domain the transfer functions and in the time-domain the different signals. Moreover, we carried out an interferometric analysis of the recorded signals in order to study the structural behaviour and to characterize the soil-structure interaction. Furthermore, we used normalized Short Time Fourier Transform (STFT) for the continuous monitoring of the structural response, in order to highlight possible frequency variations of the structural mode of vibration, and therefore of the structure’s behaviour. To assess structural frequencies and to compare them with those evaluated by transfer functions, we used azimuth-dependent Fourier spectra. We also verified the suitability of the Horizontal-to-Vertical Spectral Ratio (HVSR) for estimating the dynamic characteristics of buildings when only single station seismic noise measurements are available. Regarding the structure-soil interaction, we identified the presence of a wave field back-radiated from the structure within the low amplitude seismic noise signal. In fact, in the free-field seismic noise recording spectra, peaks at frequencies consistent with those of the first two modes of the structure were recognized.

We apply a deconvolution approach to the problem of determining the input motion at the base of an instrumented borehole using only a pair of recordings, one at the borehole surface and the other at its bottom. To stabilize the bottom-to-surface spectral ratio, we apply an iterative regularization algorithm that allows us to constrain the solution to be positively defined and to have a finite time duration. Through the analysis of synthetic data, we show that the method is capable of retrieving reliable input motion, suppressing the effect of the negative interference generated by the downgoing waves. Results obtained by applying the methodology to weak earthquakes recorded at the Atakoy (Istanbul) vertical array are also presented and show that removing the effect of the downgoing waves is remarkable, even considering the recording at a depth of 140 m.

In the last decades, researchers focused their attention on using the Rayleigh waves dispersion characteristics to estimate the shear wave velocity profile of a site, since their dispersion characteristics can be extracted also from only one component recordings (namely the vertical ones) of active and passive seismic tests. In particular, inverse analysis of empirical surfacewaves dispersion curves from microtremor measurements (passive seismic test) is a very attractive tool since it allows to keep the cost of investigation relatively low and to avoid the use of active sources that might be prohibitive in urban areas. However, until now the full potential of seismic noise array methods was not fully exploited, and, in particular, the possibility of better constraining the subsoil structure by extracting also the Love wave part from microtremors recordings has not been fully investigated.

The seismic P phase first arrival identification is a fundamental problem in seismology. The accurate identification of the P -wave first arrival is not a trivial process, particularly when the seismograms present a very low signal-to-noise ratio (SNR) or are contaminated with artificial transients that could produce false alarms. In this paper, a new approach based on higher order statistics and the stationary wavelet transform is presented. The P onset is obtained under a statistical criterion applied in the time-frequency domain. The results have been compared to those estimated by another P phase picking algorithm and P onsets picked by expert analysts. The comparison shows that our proposed method efficiently provides a good estimate of the P onset picks that are consistent with analyst picks, particularly in cases of very low SNR.

During the L'Aquila seismic sequence (Italy, 2009) we had the opportunity to install temporary accelerometric stations to study the role of seismic site amplification in damage enhancement. Two of the monitored sites, Castelnuovo and Navelli were also a good test for the recently introduced Italian seismic code (NTC08 2008) that prescribes an aggravation factor for slopes and ridges. Castelnuovo was an ideal situation to check the rule proposed for the distribution of amplification as a function of the position along a slope, while Navelli provided the possibility to test the almost equivalent factors that NTC08 sets for stratigraphic and topographic amplification (respectively up to 40 and 60 %). In neither case the observation matches code provisions. For Castelnuovo, there is a frequency dependence that shows as the code is over-conservative for short periods but fails to predict amplification in the intermediate range. For Navelli, the code provision is verified for long periods, but in the range around the site resonance frequency the stratigraphic amplification proves to be three times more important than the topographic one.

Earthquake early warning systems (EEWS) are considered to be an effective, pragmatic, and viable tool for seismic risk reduction in cities. While standard EEWS approaches focus on the real-time estimation of an earthquake’s location and magnitude, innovative developments in EEWS include the capacity for the rapid assessment of damage. Clearly, for all public authorities that are engaged in coordinating emergency activities during and soon after earthquakes, real-time information about the potential damage distribution within a city is invaluable. In this work, we present a first attempt to design an early warning and rapid response procedure for real-time risk assessment. In particular, the procedure uses typical real-time information (i.e., P-wave arrival times and early waveforms) derived from a regional seismic network for locating and evaluating the size of an earthquake, information which in turn is exploited for extracting a risk map representing the potential distribution of damage from a dataset of predicted scenarios compiled for the target city. A feasibility study of the procedure is presented for the city of Bishkek, the capital of Kyrgyzstan, which is surrounded by the Kyrgyz seismic network by mimicking the ground motion associated with two historical events that occurred close to Bishkek, namely the 1911 Kemin (M = 8.2; ±0.2) and the 1885 Belovodsk (M = 6.9; ±0.5) earthquakes. Various methodologies from previous studies were considered when planning the implementation of the early warning and rapid response procedure for real-time risk assessment: the Satriano et al. (Bull Seismol Soc Am 98(3):1482–1494, 2008) approach to real-time earthquake location; the Caprio et al. (Geophys Res Lett 38:L02301, 2011) approach for estimating moment magnitude in real time; the EXSIM method for ground motion simulation (Motazedian and Atkinson, Bull Seismol Soc Am 95:995–1010, 2005); the Sokolov (Earthquake Spectra 161: 679–694, 2002) approach for estimating intensity from Fourier amplitude spectra; and the Tyagunov et al. (Nat Hazard Earth Syst Sci 6:573–586, 2006) approach for risk computation. Innovatively, all these methods are jointly applied to assess in real time the seismic risk of a particular target site, namely the city of Bishkek. Finally, the site amplification and vulnerability datasets considered in the proposed methodology are taken from previous studies, i.e., Parolai et al. (Bull Seismol Soc Am, 2010) and Bindi et al. (Soil Dyn Earthq Eng, 2011), respectively.

The local geology and shallow S-wave velocity structure of a site are recognized to be key factors for the increase in the damaging potential of seismic waves. Indeed, seismic amplitudes may be amplified in frequency ranges unfavorable for building stock by the presence of soft sedimentary covers over lying hard bedrock. Hence, microzonation activities, which aim at assessing the site response as accurately as possible, have become a fundamental task for the seismic risk reduction of urbanized areas. Methods based on the measurement of seismic noise, which typically are fast, non-invasive, and low cost, have become a very attractive option in microzonation studies. Using observations derived from seismic noise recordings collected by two-dimensional arrays of seismic stations, we present a novel joint inversion scheme for surface wave curves. In particular, the Love wave, the Rayleigh wave dispersion and the HVSR curves are innovatively combined in a joint inversion procedure carried out following a global search approach (i.e., the Genetic Algorithm). The procedure is tested using a data set of seismic noise recordings collected at the Bevagna (Italy) test-site. The results of the novel inversion scheme are compared with the inversion scheme proposed by Parolai et al. (2005), where only Rayleigh wave dispersion and HVSR curves are used, and with a cross-hole survey.

A temporary network of 33 seismic stations was deployed in the area struck by the 6th April 2009, Mw 6.1 (Scognamiglio et al. in Seism Res Lett 6/81, 2010), L’Aquila earthquake (central Italy), with the aim to investigate the site amplification within the Aterno river Valley. The seismograms of 18 earthquakes recorded by 14 of the 33 stations were used to evaluate the average horizontal to vertical spectral ratio (HVSR) for each site and the standard horizontal spectral ratio (SSR) between a site and a reference station. The obtained results have been compared to the geological and geophysical information in order to explain the resonance frequencies and the amplification levels with respect to surface geology of the valley. The results indicate that there is no uniform pattern of amplification, because of the complex geologic setting, as the thickness and degree of cementation of the deposits is highly variable.

This paper reports on site characterization for a set of accelerometric stations of the RAN (Italian accelerometric network) with specific attention to the shear wave velocity profile. The latter is indeed of primary importance for the usability of the accelerometric database. Surface wave analysis has been chosen as the primary investigation method since it offers the possibility of reaching the required accuracy with reasonable costs. A range of different techniques, both of the active-source and passive-source types, has been adopted to cope with the objectives of the characterization in relation to specific geological settings. Quality assessment of experimental data has been implemented to check the consistency of the measurements also with respect to the fundamental hypotheses of the method. Strategies to improve the reliability and robustness of the surface wave data inversion were exploited in order to mitigate problems arising from solution non-uniqueness and influence of higher modes in the propagation. Comparisons with independent borehole tests, available at some specific sites, confirm the reliability of the results. Although the research program covered only a subset of the network, the obtained results show the importance of specific experimental investigations aimed at estimating the shear wave velocity profile. Indeed the results lead to a re-classification of several sites with respect to the preliminary classification based on surface geology. Within this context, four selected case histories are reported in the present paper.