DIGITAL SURVEY FOR THE ANALYSIS OF THE SEISMIC VULNERABILITY IN MEXICO CITY.

The recent earthquake of September 19, 2017 in Mexico mainly concerned the residential construction and heritage of towns and villages of the state of Morelos. The Mexican monuments protection agency (INAH) has started a laser scanner survey of the main buildings of the heritage at risk. The DiDA Survey Laboratory, which for years has experience both in the field of architectural surveying of monuments damaged by earthquakes, started, through the Italian Embassy and the UNAM of the City of Mexico, to document some sample cases. In March 2018 a digital surveying campaigns was carried out that involved the urban fronts of a block of the historic center of Mexico City, between the Plaza Major and the archaeological site of the Templo Major, where it was the ancient Atzeca capital of Tenochtitlan, until the Spanish conquest, built over the lake of Texcoco with palified structures; its elevated position, on strongly seismic mountains at a height of more than 2000 meters, and the geological characteristics, built on a lacustrine area above the remains of the foundations of the Aztec temples, make the buildings built on it very vulnerable. The paper analyzes the theme of methods of using digital surveys for the conservation and restoration of architecture; in the urban case, paying particular attention to the analysis of the plastic deformations and of the resistant structures, in order to evaluate the value of misalignment of the fronts of the buildings from the vertical plane and the interactions between masonries of different building units. In the case study related to Heritage, instead, attention was focused on the documentation, on the analysis of the structural conservation status, on the identification and classification of the cracks, on the verification of the main structural instabilities, and on the states of collapse. The project, still in the process of completion, presents interesting ideas for assessing and classifying risk in historic centers and in asset-value environments. The documents produced have two different purposes: on the one hand, to provide local administrations with a document through which they are able to establish the degree of risk that buildings incur in relation to preventive analyzes on the study of deformations; as for the monastery, instead, the construction of a structural consolidation project preliminary to the necessary architectural restoration.