Estudio magnético y de resistividad en los alrededores de la Pirámide del Sol, Teotihuacán, México

Abstract

The existence of tunnels and caves within the limits of the pre-Columbian city of Teotihuacan, Mexico is well known. A semi-natural tunnel was discovered several years ago beneath the Pyramid of the Sun,.ending in a four-lobed chamber. The presence of similar features in Oztoyohualco (NW of the city), led to suspect the presence of a network of tunnels beneath the city. A geophysical survey was carried out initially to calibrate the instruments on known tunnels. Then geophysical data were used to define the tunnel continuation east of the pyramid. Total field and magnetic gradient surveys were done in detail over a small plaza in front of the main stairway of the pyramid, llong with a resistivity profile using a Wenner array (S -N direction) perpendicular to the structure. The reduction-to-the-pole filter was applied to the magnetic data to define the position on the surface of the tunnel. This allowed to compute a three-dimensional model that agreed with the resistivity survey. A total field magnetic survey was performed and a series of high and low magnetic patterns were obtained. The anomalies were interpreted as magnetic signature of basaltic intrusives surrounded by caves partially filled with soil. A resistivity profile was surveyed on one of these patterns. A couple of resistivity highs were found that corresponded to the position of two caves. This result was confirmed by exploratory drilling. The anomaly was modeled with a set of three-dimensional prisms, according to the results provided by the drills and the resistivity profile. The results suggest an extension of the tunnel beneath the Pyramid of the Sun in the E direction and lend plausibility to the existence of a network of turmels beneath the city.