A new study of the Great Pyramid of Giza measures its natural “fundamental frequency” inside and finds it likely helped the Khufu pyramid avoid dangerous resonance during earthquakes—especially thanks to pressure-relieving chambers and its limestone base.
On the surface, the Great Pyramid of Giza looks like an answer to time itself. But earthquakes have never cared how famous a monument is. The Khufu pyramid endured significant seismic shocks, including earthquakes in 1847 and 1992. Now, researchers say they’ve found a structural reason it kept standing.
In a study published on Thursday in Scientific Reports, a team took dozens of measurements from inside the Khufu pyramid to characterize its “fundamental frequency”—a number that can hint at how a structure might respond when the ground starts to shake.
The idea comes from how objects move when they have a natural rhythm. Mohamed ElGabry. the study’s lead author and a professor at Egypt’s National Research Institute of Astronomy and Geophysics. compares it to a swing. A heavy push doesn’t always matter as much as the timing: it takes a lot of force to move a swing from rest. he says. but once it’s already moving. small pushes can send it flying if they match the swing’s rhythm. The same principle applies to buildings. If a building’s natural sway lines up with the frequency of the shaking ground. the effects can amplify during an earthquake. ElGabry says.
When the team looked at the pyramid, they found a mismatch that may have mattered. They reported that most of the structure has a natural frequency around an average of about 2.3 hertz (Hz). That is much higher than the ground’s frequency, which the study places at about 0.6 Hz.
The researchers also emphasized that these types of measurements aren’t new in engineering—engineers often use similar tests to assess the earthquake safety of buildings. What’s new is that nobody had made such measurements inside the Great Pyramid before. For ElGabry, the result wasn’t shocking, but it was striking: “I was not surprised, but I was impressed.”.
The most important piece of the explanation, the study suggests, is what’s built into the pyramid itself. The Khufu pyramid’s natural frequency. aided by “pressure-relieving chambers” within the structure. appears to have helped protect it from earthquakes for thousands of years. The pyramid’s foundation likely played a role as well. The team points to the fact that it was built on a limestone plateau described by ElGabry as “a very strong and massive stone. ” which helps the pyramid resist damage from earthquakes.
He also drew a clear line between what the new measurements show and what they can prove about ancient knowledge. There is no indication, he says, that the ancient Egyptians who built the pyramid were aware of these dynamics. “It doesn’t mean they knew, at that time, all the physics we know today. For sure they didn’t,” ElGabry says.
Still, the architecture of Giza tells a different story—one of trial, adaptation, and refinement through experience. ElGabry points to the design of the pyramids at Giza. as well as other ancient structures such as the Bent Pyramid in the Egyptian site of Dahshur. which has a “bend” in its shape. and the Step Pyramid of Djoser. built as a stacked rectangular prism construction. In his view. the builders were “learning by doing. ” adapting to their environment and using the resources they had to build as strong a structure as possible.
“They used it very wisely to build in a very efficient way that survived,” ElGabry says.
There’s something quietly human about that conclusion. No matter how advanced modern engineers are at measuring frequencies. the pyramid’s endurance still comes back to decisions made long before any of today’s seismic language existed—decisions that. according to these new internal measurements. may have ended up working in ways nobody could fully explain at the time.
Great Pyramid Khufu pyramid fundamental frequency earthquakes pressure-relieving chambers seismic activity Scientific Reports Mohamed ElGabry Egypt archaeology