Machu Picchu intentionally built on faults

Menegat, a geologist believes that it is not a coincidence. It would be impossible to build such a site in the high mountains if the substrate was not fractured

The Incan sanctuary of Machu Picchu – considered one of humanity's greatest architectural achievements – was intentionally built in a location where tectonic faults meet, according to a study.

Built in a remote Andean setting atop a narrow ridge high above a precipitous river canyon in Peru, The UNESCO World Heritage Site is renowned for its perfect integration with the spectacular landscape.

However, the 15th-century sanctuary's location has long puzzled scientists who wonder why the Incas built their masterpiece in such an inaccessible place.

New study presented at the Geological Society of America (GSA) Annual Meeting in Arizona, US suggests the answer may be related to the geological faults that lie beneath the site.

According to Rualdo Menegat, a geologist at Brazil's Federal University of Rio Grande do Sul, the Incas intentionally built Machu Picchu – as well as some of their cities – in locations where tectonic faults meet.

"Machu Pichu's location is not a coincidence. It would be impossible to build such a site in the high mountains if the substrate was not fractured," said Menegat.

Using a combination of satellite imagery and field measurements, Menegat mapped a dense web of intersecting fractures and faults beneath the site.

His analysis indicates these features vary widely in scale, from tiny fractures visible in individual stones to major, 175-kilometre-long lineaments that control the orientation of some of the region's river valleys.

Menegat found that these faults and fractures occur in several sets, some of which correspond to the major fault zones responsible for uplifting the Central Andes Mountains during the past eight million years.

Because some of these faults are oriented northeast-southwest and others trend northwest-southeast, they collectively create an "X" shape where they intersect beneath Machu Picchu.

Menegat's mapping suggests that the sanctuary's urban sectors and the surrounding agricultural fields, as well as individual buildings and stairs, are all oriented along the trends of these major faults.

Menegat's results indicate the underlying fault-and-fracture network is as integral to Machu Picchu's construction as its legendary stonework.

This mortar-free masonry features stones so perfectly fitted together that it's impossible to slide a credit card between them.

As master stone-workers, the Incas took advantage of the abundant building materials in the fault zone, said Menegat.

In addition to helping shape individual stones, the fault network at Machu Picchu likely offered the Incas other advantages, according to Menegat.

Chief among these was a ready source of water.

"The area's tectonic faults channeled meltwater and rainwater straight to the site," he said.

Construction of the sanctuary in such a high perch also had the benefit of isolating the site from avalanches and landslides, all-too-common hazards in this alpine environment, Menegat said.

The faults and fractures underlying Machu Picchu also helped drain the site during the intense rainstorms prevalent in the region.

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