I - 115 : The Parthenon's Incredible Resistance to Earthquake

The Parthenon survived dozens of Earthquakes over the 2'500 Years since its Construction

It is only a year ago that I wrote a blog about earthquakes in Cyprus. I had read several archeological studies which showed that many of the island’s coastal towns were once destroyed by Tsunamis. This made me wonder about current seismic activities. Low and beholed, earthquakes in Cyprus are a daily occurrence. I called the island earthquake center of the world.

Earthquakes in Greece in 2024 are 6 x more frequent than in Cyprus

At the time of writing, I did not look beyond Cyprus. But now that the media is reporting a sharp increase of seismic activities in Santorini, am having a closer look at Crete and the Peloponnese. To my surprise, earthquakes here occur about 6 times more frequently. There are 2’900 on the Peloponnese (= 8 per day), 2’300 on Crete, but “only” 445 p.a. on Cyprus.

Number and Energy of Earthquakes on the Peloponnese in 2024

The ones on Crete and the Peloponnese are also more severe. An earthquake of magnitude 6 on the Richterscale occurs on the Pelopponese every 3 years, on Crete every 4 and on Cyprus every 21 years. Clearly, the earthquake center of Europe is the Peloponnese. The cause of these quakes is for all three islands the same. The Peloponnese, Crete and Cyprus are located above the subduction zone where the African tectonic plate moves below the European plate. Its tell-tale signs are volcanoes (Thera, Nixiri) and earthquakes.

Greece's Ring of Quakes from the Peloponnese to

Rhodes - the Colour indicates the Epicenter's Debth

No wonder then that so many towns here were destroyed by earthquakes. Vulnerable were specifically abandoned cities. Once people had left in the 7th and 8th century for economic reasons, there was nobody anymore to repair the damaged roofs and walls. Due to adaptive contstruction, destruction was often less severe than we assume. Many towns shaken by quakes were quickly back on their feet. Only when unrepaired and where water seeped in did the damage become irreversible. Our ancestors had learned how to live with quakes.

Photo of the Parthenon end of 19th Century showing

how the slices Pillars absorbed earthquake stress

A good example is the Parthenon on the Akropolis of Athens. In its 2’500 years of history, it survived many earthquakes. The Parthenon’s visible damage resulted from the Turkish-Venetian war of 1699. The Ottoman stored their gun powder in the Parthenon. Unfortunately for us tourists, the Venetians used mortars during the siege. When a  grenade hit the powder magazine, the explosion blew off the Parthenon’s roof. But it is a testimony to the building’s resilience that so much of its strcture survived the powerful explosion. Its was built to resist strong vertical and lateral movements.

Parthenon Wall with Iron Hooks and Led Filling

A good decade ago, Japanese earthquake researchers took an interest in the Parthenon, a buildig that survived earthquakes for more than 25 centuries. As such, their study did not reveal any new facts. But their novel interpretation was compelling. Their simulation showed the interaction of the four resistance mechanisms which gave the building its extraordinary resilience:

• The first was the led poured between the joints of the building blocks. The metals elasticity absorbed smaller movements. When fractures or gaps appeared, molten led filled them again

• The second were the iron hooks which locked the building blocks together. They provided horizontal stability. These hooks were not rigid but had a certain wiggle room to absorb lateral movements. Each building block thus acted at a buffer, absorbing energy and slowing down the shock waves which spread it through the building

• The third defense mechanism were the pillars built slice by slice. We are used to single slab columns which decorate so many Roman Temples like the Pantheon in Rome (the granite pillars are from Egypt). Greek pillars though were never one piece.

• Last but not least, the sturdy building material played an important role. The theoretical prismatic compression structure (a big column) would have to be 4’700 km high before the stone cracks. If an earthquake lifts a roof and lets it drop down with 3 or 4 G, a limestone block can easily absorb the stress.

Earthquakes still shatter Communities like in Vathy on the Island of Samos, 30 Oct 2020

Of course, not all Greek buildings were built with the precision, care and cost of the Parthenon. Only public places were built with stone. Residential buildings were made from timber, rocks and tiles which made them more vulnerable. There is a theory that the upper floors in Greek buildings were made from wood to better absorb earthquake stress. Indeed, the elasticity of wood has its advangages, specifically when not only used for the roof but as frame for the upper walls. Stones and mortar may fall out, the frame would stay. Sadly, very few domiestic wooden structures survived. The theory has to be confirmed by more findings from future archeology digs.

This Earthquake in Kos in 2017 tore the Port Piers apart - the Tremors are powerfuf

Still, it is probably not far fetched to conclude that making buildings earthquake resilient is an ancient art which today’s engineers are discovering again. It does not surprise me though that people who were able to calculate the size of the earth (Eratosthenes did it in 240 BC in Alexandria) also built earthquake resilient buildings

Much of the Earthquake Damage has been repaired during recent Renovations