Marilena Cozzolino

Resistivity probability tomography imaging at the castle of Zena, Italy

We present the results of an electrical resistivity investigation performed at Castle of Zena (Castello di Zena), a 13th-century fortress located between the towns of Fiorenzuola and Piacenza in the Emilia Romagna Region (Northern Italy), in the frame of a project of restoration. Dipole-dipole resistivity tomographies were planned in three areas suspected of containing buried archaeo-architectural remnants. Data analysis has been made using a 3D tomography imaging approach based on the concept of occurrence probability of anomaly sources in the electrical resistivity distribution. The 3D tomography has allowed three interesting anomaly source areas to be identified in the 1-2 m depth range below ground level. Subsequent excavations have brought to light a giacciara, that is, a brickwork room for food maintenance, a furnace, and the basement of a wing of the castle destroyed in the 18th century, exactly in correspondence with the anomaly sources detected by the resistivity tomography.

Case Histories: Application of Geophysical Prospection to Cultural Heritage

The second part of this book is focused on the application of the different geophysical methodologies - Geoelectrical, Ground Penetrating Radar and Electromagnetic - to Cultural Heritage, both in Italian and foreign sites. In order to highlight the various possible applications, the case studies, related to the most frequent diagnostic surveys, have been divided into main topic: Monuments, Historical Buildings, Urban Centres, Archaeological Parks, Preventive Archeology and Ancient viability.

Management of Cultural Heritage: Contribution of Applied Geophysics

The book is based on three different concepts: Management and Cultural Heritage, and to then move toward a particular research field, that is Applied Geophysics, and the contribution that it can make. In order to get a successful management, it is necessary to achieve some requirements that include identification, protection, preservation, enhancement, fruition and transmission of Cultural Heritage to future generations. The contribution of geophysical methodologies flows into these requirements through its scope and application. The Cultural Heritage represents the fundamental recognition of the value of a territory as a symbol and an emblem of history and culture, a memory that preserves and records the changing through the time of men and landscapes, a dynamic and evolutionary proof, a sign in space and time of tangible and intangible, material and no-material actions. Cultural Heritage is a wide concept and it has changed through the time, integrating and expanding the typology of heritage included. Having at one time referred exclusively to the monumental remains of cultures, cultural heritage as a concept has gradually come to include new categories. At present, the two largest agencies engaged in the conservation and protection of the world cultural heritage, UNESCO and ICOMOS divide the Cultural Heritage into two large groups: tangible and intangible, inextricably bound up with each other. This heritage is manifested through tangible forms such as artefacts, buildings or landscapes and also through intangible forms including voices, values, traditions, oral history. This book is meant as a tool for capacity-building creation for the best cultural heritage management. The geophysical methodologies, in fact, are applications for the knowledge, conservation and enhancement of a part of the tangible heritage, especially to the archaeological and built heritage. The aim is to improve and implement knowledge, skills and competences in this scientific field and improve its decision-making and management processes through experiences developed in different approaches and in different contexts. Among the objectives set, there is the application of these methodologies in solving management issues, through a multidisciplinary approach in order to have a better knowledge and resolution of these issues.

Geophysical Methods for Cultural Heritage

The Electrical Resistivity Tomography (ERT) has been used by many geophysics for archaeological investigations since the 1960s. The electrical resistivity parameter, on which the method is based, has such a large variability to allow the great majority of the structures and bodies of archaeological and architectural interest to be readily distinguished, in principle, from the hosting material. In general, the rock resistivity depends on many factors, as water content in fissures and fractures, porosity, degree of saturation and nature of pore electrolytes. In dry state, most rocks are non-conducting, i.e. they have extremely high resistivities, which decrease rapidly with existence of fluids, usually containing various ions to form the electrolytic solution. In archaeological prospecting, the presence of a high resistivity anomaly is usually an indicator of some resistive structure, such as the presence of accumulated tiles, a stone wall, building foundation or a cavity respect to the less resistive hosting soil. Instead, the presence of a moist ditch filling in a resistive rock background is characterised by a low conductive anomaly. In the study of historical buildings, where for capillary ascent of humidity and ingression of more or less aggressive waters, internal alteration nucleuses, typically characterised by very low resistivities, become the sources of degradation and even dis-aggregation of structure. To investigate the resistivity distribution along a profile, an apparent resistivity dataset is collected by means of a device composed of a pair of energizing electrodes that sends the current into the ground and a pair of potentiometric electrodes that measures the potential difference generated by the current input. Nowadays, sophisticated low-cost multi-electrode instruments are available, which store a considerable sequence of data in a detailed way. A numerical inversion is used to convert measured apparent resistivity distributed along a pseudosection to electrical resistivity values displayed as a function of depth below surface. The geoelectric resistivity tomography (ERT) approach comes from taking many apparent resistivity determinations at as many locations as possible and involves the joint inversion of many independent tests, using an algorithm to discern subtle details from differences, which would otherwise not be seen in any one test.

Examples of Resistivity Tomography for Cultural Heritage Management

The geophysical prospections we present were realized inside the King Ferdinando IV Borbone’ Royal Residence of San Leucio (Caserta, Italy) and in the Archaeological Park of Aeclanum (Mirabella Eclano, Italy).