Mirko Corigliano

ASCONA: Automated Selection of COmpatible Natural Accelerograms

This paper describes an automated procedure for selecting and scaling real spectrum-compatible records. The methodology allows one to choose from a predefined database, assembled from accredited strong-motion accelerometric data banks, real records satisfying properly defined seismological constraints with the additional requirement of spectrum-compatibility with a reference spectrum in a specified period range. Among the different sets of records satisfying these constraints, the user can specify the desired one, based on additional requirements (e.g., limited scaling factors). The proposed algorithm allows one to select records compatible with either an acceleration or a displacement response spectrum.

Mesozonation of the Italian territory for the definition of real spectrum-compatible accelerograms

The Italian building code defines the seismic action in terms of elastic acceleration response spectra derived from the results of a probabilistic seismic hazard study performed for the whole national territory. This representation of the seismic input is insufficient for several situations (e.g. analysis of geotechnical systems or time-history analyses of structures), for which the seismic input needs to be specified in terms of accelerograms. This work illustrates a methodology for the seismic mesozonation of the Italian territory, with the aim of defining suites of 7 real accelerograms recorded at outcropping rock sites with flat topographic conditions and, most importantly, compatible with the elastic acceleration response spectrum defined by the Italian building code at any location in Italy. These accelerograms do not require any correction and can be directly used for nonlinear dynamic analyses of structures and geotechnical systems. The mesozonation is based on identification of groups of spectra with similar characteristics and shape. For each of these groups, a parent spectrum is defined and used for selecting real spectrum-compatible records. Limited linear scaling is then applied to these accelerograms to make them compatible with all the response spectra of the group. The results of this work for the 475-years return period are accessible through the SEISM-HOME Web-GIS (www.eucentre.it/seismhome.html) providing, for any site in Italy, a suite of 7 real accelerograms spectrum-compatible, on average, with the acceleration response spectrum prescribed by the Italian building code. SEISM-HOME is a useful tool for practitioners needing ready-to-use time-histories for seismic analyses.

Probabilistic Seismic Hazard Assessment at the Eastern Caribbean Islands

A probabilistic seismic hazard analysis has been performed to compute probabilistic seismic hazard maps for the eastern Caribbean region (10° N-19° N, 59° W-64° W), which includes in the north the Leeward Islands (from Anguilla to Dominica) and in the south the Windward Islands (from Martinique to Grenada), Barbados, Trinidad, and Tobago. The analysis has been conducted using a standard logic-tree approach that allowed systematically taking into account the model-based (i.e., epistemic) uncertainty and its influence on the computed ground motion param- eters. Hazard computations have been performed using a grid of sites with a space resolution of 0.025 degrees covering the territory of the considered islands. Two different computation methodologies have been adopted: the standard Cornell-McGuire approach (Cornell, 1968; McGuire, 1976) based on the definition of appropriate seismogenic zones (SZ), and the zone-free approach developed by Woo (1996), which overcomes the ambiguities related with the definition of seis- mic sources. The interplay and complexities between shallow crustal, intraplate, and interface subduction seismicity of the Caribbean region have been thoroughly investigated. By merging all available databases, a comprehensive and updated earthquake catalog for the region has been compiled. Also, a thorough investigation has been undertaken to identify the most suitable ground motion prediction equa- tions to be used in the analyses. Uniform hazard spectra have been calculated for the horizontal component of ground motion (rock and level site conditions), 4 return periods (RP) (95-, 475-, 975-, and 2475-yr), and 22 spectral accelerations (SA) with structural periods ranging from 0 to 3 s. SAs at 0.2 and 1.0 s for 2475-yr RP have been calculated to allow the definition of seismic hazard in the region of study according to the International Building Code (IBC, International Code Council (ICC), 2009).

Some Examples of 1D, Fully Stochastic Site Response Analyses of Soil Deposits

It is well known that the seismic amplification characteristics of ground motion are strongly influenced by the geotechnical properties of soil deposits and the associated uncertainties. Also the variability of the seismic input significantly affects the results of the ground response analyses. A single deterministic site response analysis, using the mean values of mechanical and physical properties of soil layers and a single recorded time history, does not allow assessing the uncertainty associated to the computed ground motion, due to the aleatory nature of model parameters and the variability of seismic input. Even a series of parametric analyses may not be sufficient, since some critical combinations of geotechnical parameters and seismic input may induce significant ground amplification that is completely overlooked by such an analyses. The uncertainty and reliability of results obtained from ground response analysis may only be achieved via fully stochastic-based procedures. This work aims at illustrating the results of 1D linear equivalent, fully stochastic site response analysis at two sites, one in Southern India, the other in Northern Italy, that have been recently carried out using Monte Carlo simulations associated with the Latino Hypercube sampling technique.

Seismic Risk Assessment of Italian Seaports Using GIS

Seaports are crucial elements in the export and import of goods and/or on the flow of travellers in the tourism industry of many industrialised nations included Italy. Experience gained from recent earthquakes (e.g. 1989 Loma Prieta in USA, 1995 Hyogoken‐Nanbu and 2003 Tokachi‐Oki in Japan) have dramatically demonstrated the seismic vulnerability of seaport structures and the severe damage that can be caused by ground shaking. In Italy, the Department of Civil Protection has funded a research project to develop a methodology for the seismic design of new marginal wharves and assessment of existing structures at seaports located in areas of medium or high seismicity. This paper shows part of the results of this research project, currently underway, with particular reference to the seismic risk assessment through an interactive, geographically referenced database (GIS). Standard risk assessment have been carried out for the Gioia Tauro port in Calabria (Italy) using the empirical curves implemented by the N...

Improving seismic hazard approaches for critical infrastructures: a pilot study in the Po Plain

AbstractPaper describes the extensive work done in the SIGMA project, aimed at improving knowledge on data, methods and tools to better quantify uncertainties in seismic hazard assessment (SHA). The authors cooperated in the study of potential faults and geological structures, earthquake catalogues, selection of ground motion prediction equations, and methods for site effect evaluation suitable for SHA. All the contributions merged into a probabilistic seismic hazard study conducted for three representative sites of the Po Plain in Northern Italy. Po Plain is a low-to-moderate seismicity region, characterized by some critical features, such as blind faulting and deep alluvium sediments, and by scarcity of strong motion data; these sources of uncertainties in seismic hazard estimation are common to other low seismicity areas around the world. Within SIGMA, special care was devoted to: (a) the use of the single station sigma approach inside the probabilistic SHA, (b) the comparative use of generalized attenuation functions to evaluate the hazard contribution of composite fault systems, and (c) the study of the epistemic uncertainties at play when different modelling approaches to site effects are used.

Parametric study of cantilever walls subjected to seismic loading

The design of flexible earth retaining structures under seismic loading is a challenging geotechnical problem, the dynamic soil‐structure interaction being of paramount importance for this kind of structures. Pseudo‐static approaches are often adopted but do not allow a realistic assessment of the performance of the structure subjected to the seismic motions. The present paper illustrates a numerical parametric study aimed at estimating the influence of the dynamic soil‐structure interaction in the design. A series of flexible earth retaining walls have been preliminary designed according to the requirements of Eurocode 7 and Eurocode 8—Part 5; their dynamic behaviour has been then evaluated by means of dynamic numerical simulations in terms of bending moments, accelerations and stress state. The results obtained from dynamic analyses have then been compared with those determined using the pseudo‐static approach.