How Incas used geological faults to build their settlements

Abstract

This communication studies the relations between Andean geo-landscape and
Inca cities by showing how the town of Machu Picchu, located at Urubamba-
Vilcanota valley, has been built. Through techniques of geolandscape
archaeology, structural geology and geomorphology, the matrix of the site was
established in terms of a very dense geological faults and fractures web. Eight
orders of network scales of lineaments and faults have been analyzed, from
both satellite images and field data. Both mountains’ and rock blocks’
geomorphology appear driven by the erosion of mutual intersection of three
main faults directions – 020º, 055º, and 330º – and two secondary directions: N-
S and E-W. The mutual interference between these faults networks led to
typical both fractal geometry of the rock blocks and structural drainage pattern.
We show that the Inca developers intentionally chose cross-tectonic faults to
build their cities. Indeed, in Machu Picchu, the rocks were so fragmented that it
was possible to build cities in high topographic levels, strategically safe against
both geological hazards and inhospitable Andean conditions. In addition, the
main sectors, buildings, and stairs were built following the three said fault
directions. According to this analysis, the Machu Picchu city plan clearly shows
the empirical fault and fracture map which underlies its construction.