How the Great Pyramid of Giza Has Withstood Millennia of Earthquakes

The Great Pyramid of Giza has survived many major earthquakes over thousands of years, with the 1992 Cairo earthquake dislodging some upper casing stones. Seismic activity may account for a cumulative height loss of about 30 feet since completion. A study measured natural vibrations at 37 locations inside and around the pyramid using an accelerometer. Most internal vibrations showed exceptional homogeneity and clustered between 2.0 and 2.6 hertz, indicating even stress distribution. Surrounding soil averaged about 0.6 hertz, creating a frequency mismatch that limits amplification of seismic energy entering the monument. The pyramid’s construction on hard limestone and internal architectural features above the King’s Chamber further reduce shockwave amplification.

"To do so, researchers used an accelerometer to measure natural vibrations at 37 locations inside and around the pyramid, including on its exterior stones, within its chambers, and in the surrounding soil. They found the majority of the vibrations inside the structure exhibited "exceptional homogeneity" and ranged between 2.0 and 2.6 hertz. This means the stress of an earthquake is distributed evenly throughout the pyramid. Crucially, this differed from the surrounding soil, which averaged 0.6 hertz, effectively offering the ground as a natural shield that prevents seismic energy from amplifying as it passes into the monument."

""This frequency mismatch between the pyramid and soil aligns with the pyramid's observed resilience against nearby earthquakes," the researchers wrote in a paper published in Scientific Reports in May. "The pyramid is distinguished by... construction on hard limestone, which was a good example of constructing a tall building on hard rock to increase earthquake resistance.""

"Over the past 4,600 years, the Great Pyramid of Giza has weathered a dozen or so major earthquakes. Most recently, the 5.9 magnitude Cairo earthquake of 1992 dislodged some casing stones from the pyramid's upper reaches. Cumulatively, seismic activity may explain why the structure has lost around 30 feet in height since it was completed at the peak of Egypt's Old Kingdom."

"Unlike the earlier Step Pyramid at Saqqara or the aptly named Bent Pyramid at Dahshur, the Great Pyramid of Giza is free from earthquake-induced structural damage. A new study led by seismologists at Egypt's National Research Institute of Astronomy and Geophysics measured such resilience and concluded that it might be partly by design."

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