Throughout the years, Italy has seen several devastating earthquakes. Central Italy is particularly to the line where the Eurasian and African tectonic plates grind against each other, resulting in vicious quakes. Yet one historic building has withstood the shaking for centuries: the Leaning Tower of Pisa. Scientists have now figured out the key to its longevity.
The Leaning Tower was built on a foundation of soft soil and constructed several floors at a time. Engineers throughout history thought that the tilt would eventually straighten out.
The Leaning Tower has struggled to stay up ever since it was finished in 1372. In 1964, the Italian government announced it was soliciting public ideas on how to prevent the Tower’s collapse and since then, efforts ranging from liquid nitrogen to soil extraction have been on the table on how to keep the architectural marvel standing. For all the worries over a collapse, it’s withstood quakes past 6.0 on the Richter Scale.
It turns out that the soil causing the tilt is part of what’s protecting the Tower from the shaking earth. The height of the Tower, 183 feet (55 meters) combined with the stiffness of the marble its built, also plays an important role. Together, all three elements modify the vibrational characteristics of the building to the extent that the Tower does not resonate with earthquake ground motion.
“Ironically, the very same soil that caused the leaning instability and brought the Tower to the verge of collapse, can be credited for helping it survive these seismic events,” says George Mylonakis of the University of Bristol, who with Italian scientists at Roma Tre University undertook the study, in a press statement.
It’s a special circumstance that has brought forth a special building. In 2013, researchers built a laser scanned 3D map of the building in order to better understand how it’s still standing. For a building nearly a thousand years old, it’s still got a few surprises left.