The historic centre of Marignane (France). Surveys and preliminary analyses

The small town of Marignane has been on the records since the period of the Roman colonisation. It nowadays presents a stratified urban structure, which is the result of subsequent enlargements of the initial settlement, based on a probable medieval allotment and expanded in modern times. A recent archaeological research carried out by the National Institute for Preventive Archaeological Research (INRAP) brought to light significant traces of the medieval structures. The main building type in the historical centre is terraced housing with two or three floors. The archaeological investigations submit that the existing blocks expanded from the inside towards the outside. The present architectonic and constructional elements of the historical centre maintain the nineteenth century arrangement. The investigation of nine blocks in the inner core of the historic centre allowed the analysis of their constructional techniques and materials, and evidenced the obvious analogies to the Provencal rural buildings. In fact, the economy of the town was predominantly rural until the end of the 1930s and, as far as the urban features are concerned, this aspect appears to have influenced the adoption of constructional methods similar to those of the countryside. This paper concerns the results of the first investigations and interpretation of the present conservation state. The implementation of a coherent framework of the most common building techniques and the major structural problems aims at understanding the specific vulnerabilities of the old buildings. The foundation on alluvial soils seems to cause the major instability phenomena. However, the presence of constructional components (flat rods) and the evidence of a specific structural behaviour (characteristic cracks) reveals a sort of “seismic memory. These observations forced us to a reflection on the impact of the past earthquakes in an area that today is not classified as a seismic one. The use of non-destructive techniques and integrated advanced instrumentation – such as ground penetrating radar and infrared thermography – contribute to better verify the use of the constructional techniques, their inherent limits and their specific resources, the conservation state and the degradation phenomena