Roberto W. Romeo

Earthquake-induced ground failures in Italy

Abstract The National Catalog of Ground Failures Induced by Strong Earthquakes in Italy (CEDIT), is described. The catalog holds data on ground failures triggered by the earthquakes that occurred in Italy in the last millennium and which had a nominal epicentral intensity equal to or greater than VIII in the Mercalli–Cancani–Sieberg (MCS) intensity scale. The ground effects reported in the catalog are the following: landslides, fractures, liquefaction, surface faulting, and topographic changes of the ground level (subsidence, settlements, tilting, and so on). Each effect is described in terms of seismological parameters of the triggering earthquake, site coordinates and administrative code, lithology and kinematic type of the ground failure. The catalog represents a tool to assess the susceptibility of geologic materials to ground shaking, and to validate predictive models of seismically induced ground displacements (scenarios of earthquake-induced geologic risks). In the context of this study, a simple statistical analysis of the database yielded useful relations between the parameters of the triggering earthquakes and the related effects.

Seismic hazard maps of Italy including site effects

The seismic hazard of Italy was mapped adopting multiple models of seismic sources, recurrence rates and attenuation relationships, and investigating the influence of site effects on assessing the earthquake hazard. This result was achieved by placing all the alternatives in a logic-tree diagram, and performing an uncertainty analysis of the main epistemic variables involved in probabilistic seismic hazard computations. Several ground motion parameters such as peak ground acceleration (PGA), velocity (PGV) and displacement (PGD), spectral accelerations at 0.2 and 1.0 s periods, and site intensities were computed. Maps of PGA and PGV values with a 10% chance of being exceeded in 50 years are shown as an illustration of the seismic hazard of Italy.

The Large Salcito Landslide Triggered by the 2002 Molise, Italy, Earthquake

The 2002 Molise, Italy, earthquake triggered a deep planar earthslide about 38 km away from the epicenter, mainly involving scaly clay shales and related weathered material. Based on site investigations and borehole data, the inferred depth of the sliding surface is between 30 and 50 meters below ground level, indicating an involved volume of about 40⋅106 m3. The complex geological setting, the generated excess pore water pressure, and possible local seismic response are thought to have been the primary contributing factors.

Soil Liquefaction During the Emilia, 2012 Seismic Sequence: Investigation and Analysis

In the framework of a Project issued by the Italian National Institute of Geophysics and Volcanology (INGV) a Research Unit (RU) has been granted with the commitment to provide a link between the seismic shaking and the triggering of ground failures such as liquefaction. The main goals have regarded both the enlargement of the base of observables for a better constrain of the seismic hazard assessments and the analysis of the triggering and causative factors of permanent ground deformations. Nevertheless, when analyzing the non-linear soil response under which liquefaction occur, some insights into site-effects have been also provided, thus contributing to the general task of the site-specific hazard. The paper illustrates the analyses and investigations carried out within the aim of the project, some of them are still provisional due to the huge amount of data produced and the strong effort required to analyze all the matters related to the observed phenomena.

Seismic Risk Analysis of an Oil-Gas Storage Plant

The wide range of induced effects of earthquakes, from direct damage due to seismic shaking to indirect damage caused by secondary effects (e.g. liquefaction, soil densification and landslides) makes the seismic risk one of the most common cause of structural failures among natural hazards. The degree of vulnerability and the level of exposure of the threatened elements may further amplify such effects. In this sense, the seismic risk induced by an oil-gas storage plant located close to an important commercial harbour in Southern Italy is analyzed. The plant is situated in one of the areas with the highest levels of seismic hazard in Italy, hit in the past by earthquakes as large as 7 in magnitude. Moreover, the plant lies near to the shoreline and the facing seafloor is characterized by the presence of a deep submarine canyon filled by loose, unconsolidated soils coming from the excavation of the harbour channel. Given these conditions the following phenomena have been investigated: local site amplification, liquefaction, submarine landslides and sea-waves run-up. The stability analyses considered both the plant’s structure itself and the site. A vulnerability analysis provided the response to the ground motions of the steel tanks forming the structure, while dynamic analyses gave the response of the soils to the wide range of possible ground failures. Joining all the possible effects that could destabilize the plant, an overall probability that the safety of the plant may be affected was computed. The total risk was then assessed considering the effects, in terms of human life losses, produced by the failure of the plant. This risk was then compared with those deriving from other human activities to provide a reasonable basis for risk the acceptability assessment.

Hazard and Risk Scenarios of Landslides Triggered by Earthquakes

This study shows, for a landslide prone area, the assessment of the slopes capacity to withstand earthquakes and how triggered mass movements can threaten potentially exposed structures and facilities. As a result a set of spatial representations (i.e., scenarios) of slope performances in a variety of seismic and climatic conditions is given and how they can induce damages or interruptions of public services such as rescue activities, communication roads, or the disruption of lifelines and urban settlements is presented.

A Performance-Based Approach to Landslide Risk Analysis and Management

An approach for the risk assessment based on a probabilistic analysis of the performance of structures threatened by landslides is shown and discussed. The risk is a possible loss due to the occurrence of a potentially damaging event. Analytically the risk is the probability convolution of hazard, which defines the frequency of occurrence of the event (i.e., the demand), and fragility that defines the capacity of the system to withstand the event given its characteristics (i.e., severity) and those of the exposed goods (vulnerability), that is: Risk=p(D>=d|S,V) The inequality sets a damage (or loss) threshold beyond which the system’s performance is no longer met. Therefore a consistent approach to risk assessment should: 1) adopt a probabilistic model which takes into account all the uncertainties of the involved variables (capacity and demand), 2) follow a performance approach based on given loss or damage thresholds. The proposed method belongs to the category of the semi-empirical ones: the theoretical component is given by the probabilistic capacity-demand model; the empirical component is given by the observed statistical behaviour of structures damaged by landslides. Two landslide properties alone are required: the area-extent and the type (or kinematism). All other properties required to determine the severity of landslides (such as depth, speed and frequency) are derived via probabilistic methods. The severity (or intensity) of landslides, in terms of kinetic energy, is the demand of resistance; the resistance capacity is given by the cumulative distribution functions of the limit state performance (fragility functions) assessed via damage surveys and cards compilation. The investigated limit states are aesthetic (of nominal concern alone), functional (interruption of service) and structural (economic and social losses). The damage probability is the probabilistic convolution of hazard (the probability mass function of the frequency of occurrence of given severities) and vulnerability (the probability of a limit state performance be reached, given a certain severity). Then, for each landslide all the exposed goods (structures and infrastructures) within the landslide area and within a buffer (representative of the maximum extension of a landslide given a reactivation), are counted. The risk is the product of the damage probability and the ratio of the exposed goods of each landslide to the whole assets exposed to the same type of landslides. Since the risk is computed numerically and by the same procedure applied to all landslides, it is free from any subjective assessment such as those implied in the qualitative methods.