EXPLORING SUBSURFACE STRUCTURES AND SEISMIC RISKS IN MESOAMERICAN HERITAGE SITES: A STUDY OF MITLA AND TEOTITLÁN DEL VALLE
In various pre-Hispanic areas of Mesoamerica, the erection of temples or elite edifices was fundamentally associated with ceremonial spaces that enabled interaction among deities, ancestors, and the living. Underneath the structures of specific ancient cities, including Monte Albán, Palenque, and Mitla, there were subterranean areas that occasionally functioned as burial chambers for rulers or other high-ranking individuals. The Spanish conquest and subsequent colonization concealed tombs and passageways that remain unexamined to this day. A recent moderate subduction earthquake caused minor damage in Mitla and other adjacent pre-Hispanic locales, including Teotitlán del Valle, highlighting the imperative to evaluate seismic risk in the region to safeguard these sites. This is especially relevant to the structural integrity of these archaeological sites, which include columns, walls, and the famous lintels.
This study employs ambient seismic noise recorded by quadrangular arrays comprising 72 vertical 4.5 Hz geophones and triaxial seismographs. We analyze the subsurface Vs structure utilizing seismic interferometry and assess seismic site amplifications through the HVSR method to evaluate the seismic response at the Mitla and Teotitlán sites. The findings indicate regions with resonances, where their lateral distribution implies the presence of potential irregular cavities with pseudo depths under 10 meters. Ambient noise tomography reveals a low-velocity zone beneath a colonial church, constructed over an ancient ceremonial plaza, which historical records and oral traditions link to a portal of the Zapotec underworld. Our ambient vibration measurements reveal substantial amplification effects that must be considered. The Mitla and Teotitlán churches demonstrate structural susceptibility owing to their vibration frequencies, presenting a risk of damage.