Interior Imaging of El Castillo Pyramid, Chichen Itza, Mexico, Using ERT-3D Methods: Preliminary Results

Abstract

The famous El Castillo pyramid, located in Chichen Itza, towards the northern portion of the Yucatan Peninsula, Mexico, is an emblematic structure of this archaeological site and recognized as one of the man-made world seven wonders. The archaeologists that restored this structure during the 1930’s discovered a smaller pyramid inside this pre- Hispanic edifice, which corresponded to an older Mayan period. The possibility of finding other construction periods inside this edifice should be important in order to reconstruct the Mayan history of the region. Previous geophysical studies carried out in 2014 by the authors, showed a buried natural cavity partially filled with water beneath El Castillo pyramid, using novel Electrical Resistivity Tomography (ERT) arrays. Employing a similar technique, a series of flat electrodes were deployed on each of the 9 bodies (or levels) conforming the pyramid plus the base of the structure, keeping a constant distance between each electrode. A precise topographic control for each electrode was fulfilled and introduced in the inversion process. 37,520 observations inside the pyramid were computed. So far, five of the 10 observation levels (19,400 points), were processed. Horizontal and vertical slices of this inverted image were analyzed. Examining the differences in the resistivity values and their gradients, allowed to locate the first substructure (explored in the 1930’s), as well as to infer a second substructure inside the previous one. An ERT-2D profile was surveyed inside El Castillo pyramid at the interior of a tunnel excavated in 1934 and the stairway of the first inner pyramid. Results from this study seem to confirm the evidence of a second substructure within El Castillo’s interior. Such feature possesses a probable intact chamber (a rectangular room 3 m high) on its upper part and inferred dimensions of 10 m high and 23 m per side at its base, assuming that the end of this profile lies on the middle of substructure 2. When the inversion will be carried out for the 10 levels, a better resolution will be reached for the upper portions of the resistivity model.