Egyptian pyramids were built to withstand earthquakes

A major earthquake struck Egypt on August 7, 1847, with its epicenter in the Fayum region south of Cairo. Records reported dozens of deaths and hundreds of buildings destroyed, while the pyramids remained standing. Analysis of vibrations inside the Great Pyramid’s tomb indicates the design dampens outside vibrational frequencies, preventing amplification of quake effects. Historical accounts say the earthquake loosened outer casing stones at the pyramids of Giza and caused some blocks to fall. The main body of the Great Pyramid and other pyramids remained largely intact and structurally sound. The pyramidal geometry concentrates mass at the bottom and lowers the center of gravity, and the Great Pyramid behaves as a single unit due to its massive block construction.

"An analysis of vibrations inside the tomb published Thursday in Scientific Reports shows how its design dampens outside vibrational frequencies, preventing amplification of quake effects. Historical accounts indicate the earthquake loosened many of the remaining outer casing stones of the pyramids of Giza, and some blocks fell off, says Mohamed ElGabry, a researcher at Egypt's National Research Institute of Astronomy and Geophysics (NRIAG) and the study's lead author. However, the main body of the Great Pyramid [and the other pyramids] remained largely intact and structurally sound, he adds."

"Architects and engineers have long noted the stability of Egypt's pyramids; for millennia, they were the tallest structures humans had ever erected. Some reasons are obvious: a pyramidal shape — with each side of the base measuring 230.33 meters and tapering as it rises to an original height of 146.59 meters, topped originally by a tiny pyramidion (now lost, leaving a 9 by 9 meter summit) — concentrates most of the mass at the bottom. That design also lowers the center of gravity."

"But that does not explain everything: the Great Pyramid of Khufu, built from 2.3 million blocks joined (and not always) with some gypsum, behaves as a single unit. Field measurements taken in the antechambers of the Great Pyramid. The inscription on the left side commemorates the discovery of the four upper chambers by Western archaeologists in 1837."

"Imagine it like a swing: every structure has a preferred rhythm at which it vibrates most easily, ElGabry says. Using a technique called the seismic HVSR method ("

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