A correlation between slope failures and accelerometric parameters: the 26 September 1997 earthquake (Umbria–Marche, Italy)

After the occurrence of the 26 September 1997 earthquake in Umbria–Marche an extensive survey was performed to individuate surface effects induced by the ground motion. Several types of effects occurred on bedrock, calcareous debris and sandy-clay deposits. Shallow soil slides and dry debris slides were mapped by field survey and aerial photograph interpretation in the epicentral area close to Nocera Umbra. This gave the opportunity for testing the prediction maps that can be obtained with the use of empirical laws, proposed by several authors, based on a simple method (Geotechnique 15(2) (1965) 139). Accelerometric records from the permanent and mobile seismic network of the Seismic Survey of Italy have been processed and interpolated to obtain strong ground motion parameters at each site, e.g. Peak Ground Acceleration, Spectral Intensity, Arias Intensity, etc. The different predictions have been tested with the real landslide data to verify their performances. Some of the proposed methods explain quite well the behaviour of slopes during the application of a time history and can therefore be employed for future landslide hazard zonation.     

Applications of statistical and GIS techniques to slope instability zonation (1: 50.000 Fabriano geological map sheet)

The aim of this work is the evaluation of the vulnerability of landslides in static, pseudostatic and dynamic conditions, to produce slope instability maps. A deterministic approach, using a GIS, (ILWIS 1.4 — The Integrated Land and Water Information System User's Manual, Enschede, 1993, The Netherlands) is presented. The analysis in static and pseudostatic conditions, using the infinite slope: analysis and the ordinary slice method, is carried out and the values of Fs (factor of safety) and Kc (coefficient of critical horizontal acceleration) are evaluated; the analysis in dynamic condition is performed, using Newmark's method, (Geotechnique, 1965, 23, 139-60), and the value of the final displacement during the application of an accelerogram is calculated. The applied methodologies and the results for the area corresponding to the NE sector of the 1:50.000 “Fabriano” (Marche Region, Italy) geological map sheet, are presented.     

Microzonation study in the Paganica-San Gregorio area affected by the April 6, 2009 L��Aquila earthquake (central Italy) and implications for the reconstruction

The earthquake of April 6th, 2009 in the L’Aquila area is one of the largest seismic events of the last years in Italy. The event, that caused significant damage in a large area of the Abruzzo region (cental Italy) and site amplification phenomena which were recorded even at large distances from the epicentre. After the emergency period, a detailed study of the surface effects was necessary for the post-earthquake reconstruction, but in a way it should be carried out rapidly enough to give instructions to urban planners, codes to public administrators and information to engineers. A team of surveyors were trained to collect field information such as geologic and geomorphologic features and geotechnical or geophysical information. The seismic inputs, for the numerical analyses, were provided, and the collected information were analyzed with the aid of dynamic codes to calculate the possible local site effects. The results are presented as acceleration response spectra, amplification coefficients (FA, FV and FH) and microzonation maps, aimed to urban planning and project design. In particular the more dangerous areas, affected by the higher amplification effects, were identified. Finally a comparison between the results obtained by the numerical analyses and the results derived from an experimental field analysis, measuring both earthquake weak motion and ambient noise, were performed. In this paper we present the results for one of the most severely damaged area (up to IX-X MCS), the Paganica–Tempera–Onna-San Gregorio area, located 6 to 10 km east of the April 6th main shock.     

Slope Instability Zonation: a Comparison Between Certainty Factor and Fuzzy Dempster–Shafer Approaches

This paper presents a comparison between two methodologies for the evaluation of slope instability and the production of instability maps, using a probabilistic approach and a hybrid possibilistic and credibilistic approach. The first is the Certainty Factor method, and the second is based on Fuzzy Logic integrated with the Dempster–Shafer theory. These methodologies are applied to the 1 : 50,000 scale Fabriano (Marche, Italy) geological map sheet. The results are represented as histograms where the accuracy of the prediction is shown, and the comparison of the results of the methods is discussed.     

Detection of local site effects through the estimation of building damages

After the Umbria Marche seismic sequence of September–October 1997, an extensive microzoning study was conducted, from October 1997 to May 1998, to detect the zones where the ground motion was amplified because of local geological and geomorphological settings. The goal of the investigation was to return amplification coefficients to local authorities for the post-seismic reconstruction and repairing of pre-existing buildings, by examining the seismic behaviour of the most damaged 60 villages. The analysis consisted in the application of well known computer codes and the results were arranged as reference table, used to assign the amplification coefficients to the rest of damaged localities.The present study has the aim of evaluating the accuracy of that methodology, following a completely different approach. The actual damages, detected by an aerial photo interpretation, are compared to the theoretical damages estimated through empirical curves, obtained from the analysis of recent Italian earthquakes. This approach was reliable enough to calibrate the results of the microzoning study and appropriate when an immediate assessment of the damage is required, to assign funds and estimate the amplification zones, that need to be investigated in finer detail.     

Prediction of Displacements in Unstable Areas Using a Neural Model

In pipeline management the accurate prediction of weak displacements is a crucial factor in drawing up a prevention policy since the accumulation of these displacements over a period of several years can lead to situations of high risk. This work addresses the specific problem related to the prediction of displacements induced by rainfall in unstable areas, of known geology, and crossed by underground pipelines. A neural model has been configured which learns of displacements from instrumented sites (where inclinometric measurements are available) and is able to generalise to other sites not equipped with inclinometers.     

Seismic microzoning of the area struck by Umbria–Marche (Central Italy) Ms 5.9 earthquake of 26 September 1997

The earthquake of 26 September 1997 in Central Italy is one of the largest seismic events of the last 20 years in Italy. Two main events that caused significant damage in a large area of Umbria and Marche regions and site amplification phenomena were recorded even at large distances from the epicenter. After the emergency period, a detailed study of the surface effects was necessary for the post-earthquake reconstruction, but in a way it should be carried out rapidly enough to allow urban planners to give instructions and codes to public administrators. A team of surveyors were trained to collect field information such as geologic and geomorphologic features and, where possible, pre-existing geotechnic or geophysic information. Information was collected and analyzed with the aid of dynamic codes to calculate the possible local site effects. A one-dimensional code, analyzing single soil columns, [Schabel PB, Lysmer J, Seed HB. , a computer program for earthquake response analysis of horizontally layered sites. College of Engineering, University of California, Berkeley, Report PB-220. 1972, p. 207], as well as the two-dimensional codes working with finite or boundary elements, [Idriss IM, Lysmer J, Hwang R, Seed HB. , a computer program for evaluating the seismic response of the soil structure by variable damping finite element procedures. UCB EERC Report No. 73-16. 1973.] and [Sanò T. , un programma per il calcolo della propagazione delle onde sismiche. Technical Report SSN/RT/96/9. 1996, pp. 51.], were used and the results are presented as response spectra or amplification coefficients.     

Evaluation of site effects using numerical and experimental analyses in Città di Castello (Italy)

In the paper the results of the numerical and experimental analyses, at a site in the Umbria Region (Città di Castello—PG), are finalized and the evaluations of site effects are shown. The aim of the work was to compare the two types of analyses and give some methodologies that may be used at the level of urban planning. Therefore a series of geological, geomorphological (1:5.000 scale), geotechnical and seismic analyses have been carried out, to characterize the lithological units and to identify the areas affected by site effects. The expected seismic inputs were provided and two-dimensional numerical analyses have been done. An experimental analysis, using the registrations of small events, has been done. The results for the two approaches were performed in terms of elastic pseudo-acceleration spectra and amplification factors. The results are given as a ratio between spectral intensity, calculated using the pseudo-velocity spectra, in the periods of 0.1–0.5 s and 0.1–2.5 s of output and input. The results have been analyzed and compared, to provide a methodology that may be comprehensive and precise.     

Lifelines earthquake vulnerability assessment: a systemic approach

This study aimed at developing a model to evaluate lifelines seismic vulnerability, considering physical, functional, and organizational factors as deeply interconnected one to the other. The resulting assessment tool consists of a set of parameters measuring the response capacity of lifelines exposed to earthquakes.

The notion of systemic vulnerability is the underlying frame of the proposed evaluation method: what can be measured is how prone is a system to damage or failure not only as a consequence of some kind of physical damage occurring to one of its components, but also as the indirect effect of some physical, functional, or organizational failure suffered by other systems.

The assessment tool has been applied in Regione Lombardia, Italy, providing as a final output recommendations for prioritizing and taking actions to reduce the potential of magnified effects as a consequence of lifelines interruption in earthquakes aftermath.     

Slope Instability in Static and Dynamic Conditions for Urban Planning: the ‘Oltre Po Pavese’ Case History (Regione Lombardia – Italy)

The paper describes a method for the evaluation of slope instability for urban planning purposes, applied in the test area Oltre Po Pavese (Regione Lombardia, Italy). A statistic and a probabilistic approach have been applied for the estimation of landslide activations and for the definition of potentially unstable areas. The displacement has been obtained through a simplified dynamic analysis, using deterministic methods: first the critical horizontal acceleration coefficient (K_c) has been evaluated, second the displacement has been calculated using the K_c values and the seismic input values, such as peak ground acceleration (PGA) and Arias intensity (Ia), through empirical relationships between displacement and Ia values for different K_c values. The results can be used by the regional government to give to the municipalities of the area a guide for the selection of the zones to be studied with future and more detailed analyses.