Scientists solve Great Pyramid's earthquake survival mystery

A team of researchers led by Asem Salama from Egypt's National Research Institute of Astronomy and Geophysics has discovered why the Great Pyramid of Giza has survived thousands of years of seismic activity without suffering major structural damage. Their study, published Thursday in the journal Scientific Reports, reveals that the pyramid's exceptional dynamic homogeneity acts as a protective shield by preventing dangerous resonance effects. The researchers found that the entire structure vibrates in unison at an average fundamental frequency of approximately 2.3 Hz, which is drastically different from the surrounding ground's frequency of 0.6 Hz, preventing mutual amplification of seismic waves. The researchers placed compact portable instruments equipped with high-sensitivity three-axis accelerometers at 37 points throughout the pyramid, including its deepest internal chambers, during periods of no human activity. They discovered that seismic amplification increases with height inside the structure, reaching a factor of 4.0 in the King's Chamber compared to the bedrock level. However, in the five pressure relief chambers situated directly above the King's Chamber, the amplification factor unexpectedly decreases to 3.0, functioning as dampers that absorb and brake seismic waves to protect the critical chamber below. The pyramid, built between 4,600 and 4,450 years ago as the tomb of Pharaoh Khufu, has endured significant earthquakes throughout history, including a magnitude 6.8 event in 1847 located about 70 km from Giza and a magnitude 5.8 quake in 1992 that only detached some upper casing stones. The study confirms that the structure was constructed on hard limestone bedrock with a low center of gravity, features that also contribute to seismic resilience. Lead author Salama noted that ancient Egyptian builders had clearly developed practical knowledge related to stability, foundation behavior, mass distribution and load transfer through trial and error, as demonstrated by the collapse of earlier pyramids like Meidum and the Bent Pyramid.