ERT for Localizing 17th Century Tunnels at a Jesuit Mission in Buenos Aires, Argentina

Abstract

We performed a geophysical study in a historical site of Buenos Aires, corresponding to a Jesuit Mission established during the 17th and 18th centuries. It consisted of a Church, the Cloisters, a School and a Procurator Office; also several tunnels were built, connecting the Mission with different public buildings of the town. In 19th century the Faculty of Sciences was constructed over one of the site, functioning until its demolition in 1973. At present, this space is a cobbled square. With the aim of preserving and restoring the buried structures, we worked in this square, looking for tunnels and also for remains of the basement of the old building. Taking into account both the conductive features of the soil, mainly formed by clays and silt, and the urban characteristics of the environment, we performed pre-feasibility studies to determine the penetration-depth of different methods. We obtained reliable data surveying with dipole-dipole profiles with apertures of 1.5 and 3 m, provided that the electrodes were buried at least 15 cm among the cobble stones. By correlating the resulting nine ERTs with the original plans, old structures and evidences of remains of tunnels were identified.