Machu Picchu: Ancient Incan sanctuary intentionally built on faults

September 23, 2019

Phoenix, Arizona, USA: The ancient Incan sanctuary of Machu Picchu is considered one of humanity's greatest architectural achievements. Built in a remote Andean setting atop a narrow ridge high above a precipitous river canyon, the site is renowned for its perfect integration with the spectacular landscape. But the sanctuary's location has long puzzled scientists: Why did the Incas build their masterpiece in such an inaccessible place? Research suggests the answer may be related to the geological faults that lie beneath the site.

On Monday, 23 Sept. 2019, at the GSA Annual meeting in Phoenix, Rualdo Menegat, a geologist at Brazil's Federal University of Rio Grande do Sul, will present the results of a detailed geoarchaeological analysis that suggests 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," says Menegat. "It would be impossible to build such a site in the high mountains if the substrate was not fractured."

Using a combination of satellite imagery and field measurements, Menegat mapped a dense web of intersecting fractures and faults beneath the UNESCO World Heritage Site. His analysis indicates these features vary widely in scale, from tiny fractures visible in individual stones to major, 175-kilometer-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. "The layout clearly reflects the fracture matrix underlying the site," says Menegat. Other ancient Incan cities, including Ollantaytambo, Pisac, and Cusco, are also located at the intersection of faults, says Menegat. "Each is precisely the expression of the main directions of the site's geological 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 stoneworkers, the Incas took advantage of the abundant building materials in the fault zone, says Menegat. "The intense fracturing there predisposed the rocks to breaking along these same planes of weakness, which greatly reduced the energy needed to carve them."

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 says. 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 explains.

The faults and fractures underlying Machu Picchu also helped drain the site during the intense rainstorms prevalent in the region. "About two-thirds of the effort to build the sanctuary involved constructing subsurface drainages," says Menegat. "The preexisting fractures aided this process and help account for its remarkable preservation," he says. "Machu Picchu clearly shows us that the Incan civilization was an empire of fractured rocks."
-end-
Session No. 148 - T126. Geoarchaeological Insights into Paleoenvironmental Reconstruction and Cultural Dynamics

Monday, 23 Sept.: 1:30 to 5:30 p.m.

Presentation time: 3:50 to 4:05 p.m.

Room 125AB, North Building (Phoenix Convention Center)

Session Link: https://gsa.confex.com/gsa/2019AM/webprogram/Session47798.html

Paper 148-9: How Incas Used Geological Faults to Build Their Settlements

Abstract Link: https://gsa.confex.com/gsa/2019AM/webprogram/Paper330598.html

Contact: Rualdo Menegat, Federal University of Rio Grande do Sul, Brazil; rualdo.menegat@ufrgs.br

The Geological Society of America, founded in 1888, is a scientific society with 22,000 members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind. Headquartered in Boulder, Colorado, GSA encourages cooperative research among earth, life, planetary, and social scientists, fosters public dialogue on geoscience issues, and supports all levels of earth-science education.

https://www.geosociety.org

Geological Society of America

Related Faults Articles from Brightsurf:

New evidence for geologically recent earthquakes near Portland, Oregon metro area
A paleoseismic trench dug across the Gales Creek fault, located about 35 kilometers (roughly 22 miles) west of Portland, Oregon, documents evidence for three surface-rupturing earthquakes that took place about 8,800, 4,200 and 1,000 years ago.

A scalable method of diagnosing HVAC sensor faults in smart buildings
Heating, ventilation and air-conditioning (HVAC) systems are the biggest consumers of energy in a building.

Researchers develop new explanation for destructive earthquake vibrations
High-frequency vibrations are some of the most damaging ground movements produced by earthquakes, and Brown University researchers have a new theory about how they're produced.

Upper-plate earthquakes caused uplift along New Zealand's Northern Hikurangi Margin
Earthquakes along a complex series of faults in the upper plate of New Zealand's northern Hikurangi Subduction Margin were responsible for coastal uplift in the region, according to a new evaluation of local marine terraces.

Machu Picchu: Ancient Incan sanctuary intentionally built on faults
The ancient Incan sanctuary of Machu Picchu is considered one of humanity's greatest architectural achievements.

Faults' hot streaks and slumps could change earthquake hazard assessments
For more than a century, a guiding principle in seismology has been that earthquakes recur at semi-regular intervals according to a 'seismic cycle.' In this model, strain that gradually accumulates along a locked fault is completely released in a large earthquake.

New map outlines seismic faults across DFW region
Scientists from SMU, The University of Texas at Austin and Stanford University found that the majority of faults underlying the Fort Worth Basin are as sensitive to forces that could cause them to slip as those that have hosted earthquakes in the past.

Many Dallas-Fort Worth area faults have the potential to host earthquakes, new study finds
A study led by The University of Texas at Austin has found that the majority of faults underlying the Fort Worth Basin are as sensitive to changes in stress that could cause them to slip as those that have generated earthquakes in recent years.

Models suggest faults are linked through California's Imperial Valley
New mechanical modeling of a network of active strike-slip faults in California's Imperial Valley suggests the faults are continuously linked, from the southern San Andreas Fault through the Imperial Fault to the Cerro Prieto fault further to the south of the valley.

Catalog of north Texas earthquakes confirms continuing effects of wastewater disposal
A comprehensive catalog of earthquake sequences in Texas's Fort Worth Basin, from 2008 to 2018, provides a closer look at how wastewater disposal from oil and gas exploration has changed the seismic landscape in the basin.

Read More: Faults News and Faults Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.