Wednesday, 17 August 2016

Earthquakes and architecture – ancient and modern in Peru

By Lindsey Atkinson

Peru lies on the western side of South America: approximately 100 miles off the coast in the Pacific Ocean the Nazca plate is subducted under the South American plate forming the Peru-Chile (Atacama) Trench.  As a result Peru is subject to frequent earthquakes* and sometimes even tsunamis (e.g. 1996 and 2001). 

Adobe house
 Approximately two-thirds of Peru’s rural population live in adobe dwellings which are particularly vulnerable to collapse during an earthquake.  Adobes are made out of sun-baked clay bricks and it is only possible to build up to two floors.  Professor Marcial Blondet and his team at the Catholic University of Peru in Lima have been working to make adobe buildings safer (http://news.bbc.co.uk/1/hi/world/americas/8202498.stm) using a polymer mesh for reinforcement.  They recommend keeping buildings to one storey and keeping the size of openings to a minimum for greater strength. Today although people in rural areas still build their own adobe houses, in many towns most buildings are now constructed with steel reinforced concrete which allows for much taller structures.

Huaca Pucllana
How did ancient Peruvians cope with earthquakes without the benefits of modern technology?  The temple of Huaca Pucllana in Lima (http://huacapucllanamiraflores.pe/) was built by the Lima culture between 200 and 500 AD and is an adobe ‘pyramid’.   This mud structure, now partially reconstructed, has survived so long, partly due to the extremely low rainfall in the region, but also because of its construction with bricks placed vertically and spaced to allow for movement during earthquakes.

The Incas (1200-1542 AD) built with stone.  For example the temple of Qorikancha in Cusco (https://www.cuscoperu.com/en/travel/cusco/archaeological-centers/qorikancha) demonstrates fine masonry with large, well–fitting, rectangular blocks of stone.  No mortar was used, but a fine layer of sand between blocks allows for some movement during an earthquake.  The structure has inward sloping walls which provide stability and it is said that the trapezoid niches and doorways help dissipate the energy of seismic tremors.  Sites such as Sacsayhuaman near Cusco have well-fitting, but this time, irregular shaped blocks.  This degree of craftsmanship seems to have been reserved for religious sites and for the nobility: other sites have rougher stonework with mud mortar and square niches.  

Sacsayhuaman
Qorikancha


Lima Cathedral
The Spanish colonial builders were not so successful: many of their buildings collapsed during earthquakes, while Inca structures remained. For example, the convent of Santo Domingo in Cusco was built on top of Qorikancha, using the temple as its foundations but while the convent had to be rebuilt following the 1950 earthquake the Inca walls stood undamaged.  The cathedral in Lima dates from 1535 but has suffered damage following many earthquakes and in 1746 it was completely flattened.  The current building has wooden, rather than stone, columns and a wooden ceiling plus a policy of strictly no candles!  However, the catacombs beneath the nearby Monastery of Saint Francis, built of bricks and mortar, do seem to have survived quite well.  These crypts also include well-shaped structures which again are said to dissipate the lateral energy of a tremor.

Probably the most famous site in Peru is the citadel of Machu Picchu, abandoned shortly after the Spanish Conquest in the mid-1500s: one theory is that this was to prevent it from being found by the Spanish.  It remained hidden to all but local farmers until 1911 when it was rediscovered by the American explorer, Hiram Bingham.  The ability of these structures to withstand earthquakes is largely anecdotal and have not been proven, although modern techniques allow for better assessment of their earthquake protection properties (see Cuadra et al. 2008). So far Machu Picchu has proved to be remarkably earthquake resistant.

Machu Picchu


*Most recently on 15.08.16 (http://www.bbc.co.uk/news/world-latin-america-37084723)

Bibliography
Bankoff G. 2015. Seismic architecture and cultural adaptation to earthquakes. In: Kr├╝ger F, Bankoff G, Cannon T, Orlowski B, and Schipper L, eds. Cultures and disasters: Understanding cultural framings in disaster risk reduction. New York and London: Routledge.
Blondet M, Villa Garcia GM and Brzev S2003. Earthquake-Resistant Construction of Adobe Buildings: A Tutorial. Published as a contribution to the EERI/IAEE World Housing Encyclopedia, http://www.world-housing.net/wp-content/uploads/2011/06/Adobe_Tutorial_English_Blondet.pdf
Cuadra C, Karkee MB and Tokeshi K. 2008. Earthquake risk to Inca’s historical constructions in Machupicchu. Adv. Eng. Software 39: 336-345. http://dx.doi.org/10.1016/j.advengsoft.2007.01.002.
Smith J and Petley DN. 2007. Environmental hazards: assessing risk and reducing disaster. 5th edn.  New York: Routledge.
Stewart A. 2013. The Inca Trail, Cusco and Machu Picchu. 5th edn. Trailblazer Publications. Surrey, UK