Chile and Peru are two of the countries with the highest seismic activity in the world. Since ancient times, its inhabitants have faced earthquakes in their buildings. Surprisingly, the contributions of ancient pre-Hispanic knowledge may have made some buildings withstand centuries and earthquakes. Therefore, they could serve as inspiration for new anti-seismic structures.
An ‘earthquake’ shakes Santiago during the week we visit the Chilean capital. that’s how they differ here mild seismic events, around 5 degrees, those of greater magnitude, earthquakes. The tremor causes a landslide on one of the city’s hills, but for the regular inhabitants of the Maipo Valley it is still part of an acquired routine.
It is also common for san francisco church. The temple, located in the heart of the city, celebrates its 405th anniversary this year. This means that it withstood about 15 earthquakes of great magnitude, which made it the object of scientific study to explain its extraordinary seismic resistance.
An earthquake-resistant temple
The case of this temple is emblematic. It is the oldest building in Chile. Its works began between 1583-1586, ending in 1618. Although some sources consider that the church of San Francisco de Chiu-chiu —in the north of the country— is the oldest building, its date is undetermined and it is dated with a vague “in the middle of the 17th century”.
“In its 405 years of history, the church of San Francisco de Santiago has withstood more than 15 earthquakes above magnitude 7. The earthquake of 1647, the most important of them, had a magnitude of 8.5 and, according to the chroniclers, all the buildings of Santiago were on the land, except for the church and part of the convent of São Francisco”, explains Carolina Vergara, architect and director of the San Francisco Museum.
The temple originally had a transverse plan, built with large stone blocks. At the end of the 18th century, brick side aisles were added, losing the cross shape and acquiring the rectangular shape that it currently has.
Although the earthquakes meant that the church tower had to be replaced up to three times — the fourth and current one being in 1856 — the structure of the temple only suffered light damage from seismic origin.
Skating church survives earthquakes
In 2016, Natalia Jorquera, an academic at the Department of Architecture at the University of Chile, It isyouhated the church to understand the secret of its seismic resistance “despite the apparent fragility of the construction materials used, with low resistance to horizontal forces”, he explained in his article.
The architect found that the Mudejar coffered ceiling had improved the building’s seismic performance while maintaining the thick stone walls 1.7 meters wide. That had already been praised by the chroniclers of the time.
But the professor made a discovery. Upon examining the foundations, he found that the thick walls were simply supported on movable supports, without mortar. These consisted of boulders (or ‘bolones’) of between 10-30 cm submerged in earth and loose sand. They were confined laterally by two large axes of megalithic stones, which prevented them from spreading. In this way, in the event of an earthquake, the building would “skate” on its foundations.
“It is likely that an attempt was made to use seismic isolation with the round stones in the foundation.”, explains Julio Vargas Neumann, emeritus professor at the Catholic University of Peru (PUCP). But the expert warns that giving too much anti-seismic capacity to mobile foundations could be “optimistic”, because bolons were only found in one part of the building.
Faced with the impossibility of excavating inside the church, Jorquera’s team used a georadar to check the interior of the walls. The professor adds in her article that “presumably this foundation system is the same throughout the church, but given the limitations of the excavated surface this would remain a hypothesis”.
The crossroads between two worlds
“The Spaniards founded Santiago in 1541, just 40 years before the church was built and there had yet to be a major earthquake in the area. If they come from an environment with low seismicity, it is unlikely that they have presented the foundation solution.Jorquera argues.
For the architect,the church of São Francisco manifests the crossroads between two worlds. The Spanish constructive contribution is made on the roof, with some beams in a clearly Spanish Mudejar style. At the bottom is a very local building, the result of pre-Hispanic architecture that was taken to another scale and form. I think that’s cool, because it manifests a tangible understanding between two worlds.”.
“The Europeans arrived and implemented an abstract architectural model, which is the Catholic temple: to worship God you have to find yourself in a closed space, it has to fit a lot of people and the space has to be long and very high, because it is divine. In addition, it must be in the form of a cross. This abstract approach reaches a territory with earthquakes, where there are already people with some empirical knowledge about anti-seismic construction.”, says Professor Jorquera.
ownerless innovation
Although studies have verified the building’s extraordinary seismic performance, at the moment not much is known about its construction. The San Francisco archives do not list the people who participated in the work, but the materials and financial requests to the Spanish crown are listed.
“The building is very well done. That it is dissipating seismic energy, there is no doubt. Probably, if there is any thinker who has done so, he could not transmit his knowledge more”, reflects Vargas Neumann.
“We’ll never know who invented it, but it’s pre-Hispanic. The walls of San Francisco have stonework and masonry identical to constructions in the north of the Chilean Andes, such as in the region of Antofagasta. There is clearly a direct relationship, although it is not documented in a historical file with first and last name.Jorquera explains.
Looking for information on earthquake resistance: the shicras of Caral?
In fact, the church is not an isolated example. Further north on the continent, in Peru, Inca constructions are preserved at Machu Picchu and sacsayhuaman studied for its resistance to the passage of centuries and earthquakes.
Even further back in time, at the 5,000-year-old archaeological site of Caral (Peru), rope bags filled with stones (shicras) were discovered under the foundations of some buildings. Just a few years before Professor Jorquera’s research.
Renowned engineer Vargas Neumann, 82, has spent more than 50 years studying earthquake-resistant earth construction. In 2011, he led a team that studied the shicras found in Caral and along 400 km of the north-central Peruvian coast. The investigators warned that these bags could contribute to improving the anti-seismic behavior of the pyramids, similarly to the foundations of the church of São Francisco.
However, the emeritus professor at PUCP demystifies the anti-seismic knowledge of America’s oldest civilization. “The shicras were not placed because it was concluded that the energy that comes from the earth’s crust, from bottom to top, is dissipated when passing through the layers of pockets and that this way the upper part of the pyramid was preserved. If so, they would have done it well, with clear criteria.”.
In the opinion of the renowned engineer, the shicras were deposited for another purpose. “The Caraleños must have realized that the bag full of stones constituted a constructive unit in itself. Accumulating full Shicras increased efficiency compared to having to unload the stones and return to the quarry with an empty bag.“, Explain. They would be a kind of ancestral gabions.
Rope and stone houses to withstand earthquakes
Vargas Neumann’s desire to test Caral’s technologies led him to wonder whether they could be realized. earthquake resistant buildings today with those shicras of rope and stone.
For this purpose, the teacher carried out some essay on the university shaker table. The studies ended with a prototype house —which proved to be very economical— that dissipated seismic energy through modern shicras. The prototype was installed in Orduña (Peru), and later the city suffered a destructive earthquake that only caused cracks and small landslides in the house. The trial was a success.
“It had nothing to do with Caral’s ancestral knowledge. It is a modern study that has worked based on ropes and stone. However, if it weren’t for the belief that those ancient shicras were earthquake resistant, we would never have done the research at the university.”, explains the Peruvian academic.
Professor Julio Vargas Neumann is currently seeking to certify this constructive technique in the Peruvian Standard for Design and Construction of Reinforced Earth. For this, it must be submitted to the approval of a commission of the Ministry of Housing, according to the engineer himself.
no building is eternal
Despite the good seismic performance of some historic buildings, the awareness that citizens have of their heritage also has an important impact on their conservation.
“It is a privilege for us Chileans to have a building as old as the San Francisco church in this seismic country. This does not mean that it is an eternal construction. There can always be a big earthquake and you won’t get over it.”, recognizes Carolina Vergara, director of the San Francisco Museum.
In October 2019, there was no earthquake, but there was a social outbreak that put the temple in Santiago at risk. In the context of the protest, churches were set on fire and vandalized. The neighboring church of São Francisco de Borja, built in 1876, suffered the same fate. It held the oldest stained glass windows in the country, lost forever. Its burnt and isolated ruins still bear witness to those uncertain days.
As in previous earthquakes, the social outbreak also left visible wounds in the church of San Francisco. Robust metal plates had to be installed to protect its doors and windows. And the facades were covered in graffiti. Despite everything, the temple continues to withstand the shocks of the years. I hope for a long time.
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