Simone Barani

Assessing the Effectiveness of Soil Parameters for Ground Response Characterization and Soil Classification

The average shear wave velocity over the top 30 m of a soil profile (VS,30) represents an usual parameter for soil classification in a modern building code for seismic design. In this work the ground response of about 100 soil profiles in Tuscany and Molise (Italy) is studied through 1-D numerical simulations in order to evaluate the reliability of European and Italian soil classifications based on the VS,30 criterion. The amplification factor, Fa , defined here as the ratio of the pseudo-velocity response spectrum intensity (Housner 1952) at the surface, S Is , to the pseudo-velocity response spectrum intensity at the rock outcrop, S Ir , is related to some soil parameters, such as VS,30, the fundamental frequency of vibration of the soil column, F0, and seismic impedance contrast, Iw . Analyzing the standard deviation of the residual obtained from regression analyses of Fa versus VS,30, F0, and Iw shows that F0 is the most helpful parameter for the prediction of Fa . Hence F0 appears to be more appropriate than VS,30 and Iw for the characterization of the seismic response of a site and, therefore, should not be disregarded in building code soil classifications.

Influence of Soil Modeling Uncertainties on Site Response

The scope of this work is to examine the influence of the uncertainty in soil modeling on numerical ground response estimates through a comprehensive sensitivity analysis. This allows identification of those parameters with the largest effect on both soil amplification (quantified here by a frequency-independent factor, Fa) and fundamental frequency, f0. Although extensively examined in previous articles, the effect of the input motion is also analyzed. The uncertainty affecting the shear wave velocity (VS) profile was found to be the factor contributing most to the uncertainty of both Fa and f0. The soil thickness was also found to play a key role, particularly in those cases where bedrock depth is unknown or largely uncertain. Although of secondary importance compared to the effect of VS on Fa and f0, the influence of the input motion cannot be neglected; rather it becomes predominant with regard to the uncertainty affecting frequency-dependent shaking parameters.

Soil amplification in probabilistic ground motion hazard analysis

The article presents a comparison of different probabilistic methods for ground motion hazard assessments that include site effects. The approaches examined here were selected and refined during the different phases of the S2-Project, which this journal volume is addressed to. Different procedures characterized by different levels of sophistication, from the simpler one based on the use of standard ground motion predictive equations for specific ground types to the more complex one based on the convolution of a site-specific amplification function (and its variability) with the hazard curve for reference rock, are compared and contrasted with the aim of pointing out strengths and weaknesses of each of them. In addition, a fully non-ergodic approach that separates the epistemic contribution (i.e., the epistemic uncertainty affecting the soil properties) from the total variability in site amplification is presented. To fulfill the scope of the work, the study focuses on three test sites in Italy characterized by different geological conditions and seismicity levels: Mirandola and Soncino in the Po Plain (northern Italy) and Peglio in central Italy.

On the Influence of Horizontal Ground‐Shaking Definition on Probabilistic Seismic‐Hazard Analysis

Abstract The impact on probabilistic ground‐motion hazard of different definitions of the horizontal component of ground shaking is examined. The scope is to highlight how such a minor detail within the complex computation chain of a probabilistic seismic‐hazard assessment can play a crucial role on final results. This is achieved by comparing hazard maps produced for Italy considering different definitions of the ground‐motion component at different spectral periods. In our exercise, special attention is paid to the treatment of the aleatory variability of ground motion (sigma) when one switches from one metric to another. The results show that differences in the definition of the horizontal component could imply differences in the hazard results as large as 40%. Online Material: Color maps of geographical distributions of hazard value ratios.

Long-range dependence in earthquake-moment release and implications for earthquake occurrence probability

Since the beginning of the 1980s, when Mandelbrot observed that earthquakes occur on ‘fractal’ self-similar sets, many studies have investigated the dynamical mechanisms that lead to self-similarities in the earthquake process. Interpreting seismicity as a self-similar process is undoubtedly convenient to bypass the physical complexities related to the actual process. Self-similar processes are indeed invariant under suitable scaling of space and time. In this study, we show that long-range dependence is an inherent feature of the seismic process, and is universal. Examination of series of cumulative seismic moment both in Italy and worldwide through Hurst’s rescaled range analysis shows that seismicity is a memory process with a Hurst exponent H ≈ 0.87. We observe that H is substantially space- and time-invariant, except in cases of catalog incompleteness. This has implications for earthquake forecasting. Hence, we have developed a probability model for earthquake occurrence that allows for long-range dependence in the seismic process. Unlike the Poisson model, dependent events are allowed. This model can be easily transferred to other disciplines that deal with self-similar processes.

Analysis of Site Amplification Effects at Four Installation Sites of the National Accelerometric Network (RAN) in Italy

The purpose of this work is to study seismic amplification effects at four sites hosting recording stations of the National Accelerometric Network (RAN) managed by the national Department of Civil Protection. At all sites, which are located in the Piedmont region (Northwestern Italy), both active and passive seismic prospecting methods are used, allowing identification of local amplification effects at three out of the four sites analysed. A ground type is then assigned to each site according to the national antiseismic code. Results obtained here will be fundamental to reduce the ground motion variability related to ground motion prediction equations and, consequently, to produce finer site-specific ground shaking hazard maps.

An Integrated Geophysical-geochemical Approach for Soil Precision Mapping in a Cinque Terre Vineyard (Italy)

Summary The study has presented an integrated approach to viticultural soil characterization using geophysical and geochemical methods. The purpose of this work is to evaluate the presence of geophysical and geochemical anomalies in soil within a vineyard located in well-known Cinque Terre Zone, North-Western Italy. To this scope soil and bedrock features have been studied with electromagnetic induction (EMI) and spettrophotometry method: both the methods have allowed to realize maps of conductivity anomalies values and major chemical elements distribution respectively for the investigated area. Although still at a preliminar stage, the results presented here are encouraging, indicating a good agreement between EMI and EDXRF data. The geological heterogeneity of the study area is clearly reflected both in the conductivity data and in the geochemical composition of the near-surface soils examined. The approach applied here can be extended to larger agricultural areas used by the agrofood industry, either alone or with the aim of integrating data from standard approaches based on pedological analysis. Correlation among data of different nature can nowadays be simply examined through the use of GIS software