Built during the Old Kingdom for the pharaoh Cheops, the great pyramid of Giza has fascinated people for millennia. Beyond its gigantic size and its perfect astronomical alignments, it hides a much more discreet, but equally impressive feat: its phenomenal resistance to earthquakes. While many modern buildings collapse during violent tremors, this stone giant has gone through time almost without flinching, having only lost around ten meters in height in more than forty-six centuries of existence.
However, there is nothing magical about this architectural miracle. Over the ages, the monument has suffered major earthquakes, notably an earthquake in 1847 estimated at a magnitude of 6.8, south of Cairo, and another of 5.9 in 1992 which still caused some stones to fall from its summit. To understand how such a mass of limestone can absorb this type of shock without collapsing, an international team of researchers looked into its internal vibrations, lifting the veil on strikingly modern engineering.
In a study published in the journal Scientific Reports, geoscientist Asem Salama and his team analyzed data collected by 37 motion sensors installed throughout and around the building. By recording the ambient vibrations when the site was completely empty of tourists, the experts highlighted an astonishing phenomenon: the pyramid vibrates at a natural frequency, located between 2 and 2.6 hertz, while the natural ground which surrounds it oscillates at a much lower frequency, around 0.6 hertz.
This major difference creates a sort of wave break, summarizes a Live Science article. During an earthquake, the Great Pyramid of Khufu behaves autonomously and somehow separates itself from the violent tremors that pass through the ground, thus avoiding the resonance effect that usually destroys buildings. “The study highlights the extraordinary practical engineering knowledge of ancient Egyptian builders, who developed highly efficient construction methods through centuries of experimentation and refinement”explains Asem Salama enthusiastically.
Useful secret rooms
If the perfect symmetry of the building, its gigantic base and its ultra-robust limestone foundations explain a large part of its solidity, researchers have discovered another well-kept secret at the very heart of the structure. By measuring the evolution of the waves from bottom to top, they noticed that the natural accentuation of vibrations towards the top – a phenomenon well known to skyscraper architects – is suddenly broken halfway.
This attenuation is believed to be due to the “discharge chambers”, five mysterious cavities superimposed just above the king’s burial chamber, approximately 61 meters high. Originally designed by workers to distribute the titanic load of the granite ceiling and prevent the room below from collapsing, these chambers actually play a crucial second role: they act as seismic shock absorbers, absorbing energy before it reaches the top.
This dual function shows to what extent the Egyptians of the time possessed extraordinary knowledge. Far from being the result of chance, each element of the pyramid seems to have been designed to guarantee the eternity of the royal residence. The lessons learned on this colossal project made it possible to design a monument capable of dissipating one of the most powerful energies on our planet.
Beyond simple historical fascination, these unique acoustic analyzes open the way to new conservation methods for world heritage. By understanding the internal dynamics of these ancient structures, today’s engineers hope to develop long-term preservation strategies capable of protecting the Great Pyramid for centuries to come, without ever altering its original integrity.
