GPR measurements to identify cracks and textural arrangements in the altar wall of the 16th-century Santa Maria Huiramangaro Church, Michoacan, Mexico

A three-dimensional ground-penetrating radar survey was performed on the altar wall, which faced the risk of collapse, of a 16th-century church in Michoacan, Mexico. The ground-penetrating radar survey with high-frequency antennas aimed to locate structural cracks and texture arrangements, the latter through the interpretation of the patterns in the electromagnetic data. The results indicate that the superficially visible cracks or fractures, except for the lateral ones at each end of the wall, disappear at a depth of between 15 and 25 cm. The lower part of the wall below a height of 3.97 m presents an area with multiple diffractions, which suggests that the masonry is made of 'stone and mud' and the tilt appears precisely where the adobe wall starts. Using 1500 and 900 MHz antennas, the identified texture of the wall shows at least three leaves or layers with diverse materials and a wooden beam embedded in the wall. Additionally, the survey near the church with a 200 MHz antenna supports the hypotheses that local construction materials were used here. The results inspire us to continue applying ground-penetrating radar, a non-destructive method, to diagnose the walls and structures of historical monuments before any intervention.