Roman amfiteatre are among the oldest human structures on Earth. These structures are amazingly well preserved in different locations across the ancient Roman Empire. This is particularly noteworthy since a considerable part of the territory of the seismic activity: it is located on the tectonic boundary of the Eurasian and African plates and has experienced numerous earthquakes that have destroyed other types of buildings. As amphitheatres survived these 2000 years — that is the question.
The secrets of Roman architects
Today we can get a potential answer thanks to the work of Stephen Brulle and his colleagues from the University of AIX-Marseille in the South of France. These guys have figured out something, as certain structures dig into the ground or holding it, can change the way of propagation of seismic waves through the Earth. In particular, they studied the “seismic invisibility cloaks” that can send seismic waves to wrap around certain areas, thus protecting them.
Scientists came to the conclusion that Roman amphitheatres can act as seismic cloaks of invisibility due to its shape. This was the reason for their remarkable longevity.
But first, a little background. Physicists have long known that certain regular patterns of objects can interact with the waves in such a way to manage and change their behavior. A curious feature of this phenomenon is that the objects themselves are much smaller the waves themselves. But the total effect of a set of objects located in a certain structure, has an important influence on the waves.
Back in 2006, physicists used this idea to create a structure of metallic resonators that direct the microwaves around the area of the space. To the casual observer who looks at the microwave, this area of space and everything in it disappears. Using this effect, scientists have created the world’s first invisibility cloak.
Since then, scientists have created invisibility cloaks for a wide range of different waves in the electromagnetic spectrum and beyond. In 2012, they suggested that the seismic invisibility cloaks can protect power plants and dams from earthquakes. Then Bruhl and his colleagues have created and tested the following.
Since then, scientists have continued to investigate the seismic metamaterials, which, according to them, can take many forms. Early experiments included underground structures or cavities. But more recent work suggests that surface objects, trees or buildings can also affect seismic waves.
One of the ideas is that the seismic waves cause the vibration of the skyscraper. But the vibration sends waves through the earth. Thus, if two sets of waves could suppress or extinguish each other, the building would have a significant moderating effect on the waves.
Brühl and colleagues even carried out experimental measurements of the waves generated by the skyscraper as the result of seismic noise. Considered LatinoAmericana Tower is a 282-meter skyscraper in Mexico city, has experienced several major earthquakes since its construction in 1956.
Scientists have developed a computer model to explore how arranged in a circle skyscrapers can act as a cloak of invisibility, creating a safe zone in the center. “The seismic waves will affect the building in the annular space of a Cape and beyond, but the area in the center (e.g., Park) would be a safe area where people can gather to stay safe during an earthquake”, they write.
In the course of these studies they noted the similarity between the circular diagrams that they have created, and design of ancient amphitheatres. “There is a striking resemblance between the cloak of invisibility tested on different types of waves, and aerial photos of the antique Gallo-Roman theatres”, says they. “Maybe that’s why some of these megastruktur, such as the amphitheater, was left mostly untouched for centuries.”