Hidden structural features inside Egypt's Great Pyramid may have helped it withstand earthquakes, new study finds

The Great Pyramid of Giza, built about 4,600 years ago, has remained standing despite weathering and seismic events, including earthquakes in 1847 and 1992. Scientists investigated why by measuring the pyramid’s fundamental frequency, a property that indicates how a structure naturally sways and how it may respond to earthquake shaking. Measurements were taken inside the Khufu pyramid, including in the relieving chambers. The researchers found that most of the pyramid has a natural frequency averaging about 2.3 hertz. This value is much higher than the ground’s frequency of about 0.6 hertz. When a structure’s frequency matches the ground, earthquake effects can amplify, but the mismatch in this case likely limits amplification.

"Researchers took dozens of measurements from inside the Khufu pyramid to characterize its fundamental frequency, a measure that can inform how a building might respond during an earthquake. You can think of a building's fundamental, or natural, frequency like the sway of a swing. It might take a lot of force to move the swing from a still position. But at a certain point, even just a small push to a moving swing can send it flying. A similar effect happens in structures: a building's natural sway affects how it responds during pushes or earthquakes."

"If a structure has the same frequency as the ground below it, that can amplify the effects of an earthquake, he says. That's not the case for the Khufu pyramid, ElGabry and his colleagues found. They discovered that most of the structure has around the same frequency, an average of about 2.3 hertz (Hz). That's much higher than the ground's frequency of about 0.6 Hz."

"Field measurements are taken in the Relieving Chambers of the Great Pyramid. The researchers took dozens of measurements from inside the Khufu pyramid to characterize its fundamental frequency. The study used these measurements to determine how the pyramid’s natural sway compares with the frequency of the ground during seismic activity. The resulting comparison indicates whether earthquake shaking would be amplified by resonance."

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