The Great Pyramid of Giza, also known as the Khufu pyramid, is among the most famous wonders of the ancient world. It is also a wonder that the structure is still standing—given that it was erected some 4,600 years ago and has had to withstand significant weathering and seismic activity over that time, including earthquakes in 1847 and 1992. Why the pyramid could withstand such trauma hasn’t been fully understood, but now scientists are beginning to unearth some answers.
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, says Mohamed ElGabry, the study’s lead author and a professor at Egypt’s National Research Institute of Astronomy and Geophysics. 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.
