Devastation of the 1956 Earthquake

The year is 1956 and Santorini is as beautiful as it has always been with its white and blue adobe buildings perched on the caldera cliffs. The markets are filled with venders eager to sell their fresh produce. Profitis Ilias is looming over the city like a Sheppard watching over his flock. To any regular native of Santorini this seems like another day of business and enjoyment.

Then without warning, comes a random jolt that impacted the island. All of the sudden the ground begins to shake. This shaking is so intense that people fall over due to the sheer force of this back and forth motion. People franticly run in every which direction, looking like thousands of ants scurrying for their lives, trying to find some sort of cover from this chaos. Buildings begin to collapse due to the instability of the slopes. Landslides dominate the landscape, as loose patches of sediments are revealed and take parts of the city with it.

This hellish nightmare continues damaging establishments that have been prominent on the island for years. The shaking completely wipes out sections of the city while giving other parts a new type of remodeling. Once the shaking final stops, there is no longer a familiar city but an island in ruin and despair.

(Figure 1) A picture of the aftermath in Oia. Retrieved from (http://www.santorini-hotels.info/tourist-guide/oia/oia-santorini.htm)

On the 9th of July, an unexpected 7.7 magnitude earthquake struck Santorini and other nearby islands [1]. At the end of this 12 minute ordeal, more than a thousand buildings had suffered damage while about 300 had been completely destroyed [1]. This was one of the most powerful earthquakes recorded in the Aegean Sea, both Oia and Fira had incurred the greatest amount of damages by the end [1].

image
(Figure 2) Picture of the origin of the earthquake and its distance from Santorini.

The first concept to understand about earthquakes is how they originate. Energy is created due to movement along faults where each side of the fault moves in opposite directions, building tension. The 1956 earthquake originated on a strike-slip fault, this fault is known as the Amorgos fault. An easy way to think of this would be taking two dish sponges, putting them side by side and pulling them in different directions.

Fault
(Figure 3) Movement of a strike-slip fault and place where tension occurs.

Instead of having smooth sides to slide by one another, the massive structures of rock get caught on uneven surfaces and builds up stress. This stress accumulates over time gathering a greater amount of energy. Once this energy has reached its limit, the sides then give and slip past each other, releasing energy that radiates in all directions.

The two main waves that are released from earthquake events are P-waves and S-waves (seismic energy). P-waves are the fastest of the waves, due to traveling through compression, which mean they are the first to be felt. This wave can be compared to the jolt you would feel from the kickback of a 12-gauge shotgun. It can travel through gases, liquids, and solids which makes it an effective warning system, due to its arrival before the S-wave.

S waves, on the other hand, are the highly destructive waves that follow the P wave. These waves have more of a wavy, side to side motion, like holding a slinky at both ends and shaking it back and forth. Unlike the P-waves, S-waves are not able to move through liquids but if they reach a patch of loose, saturated sediment then they can deliver loads of damage. This happens due to the lack of compaction and the space between molecules allows for the waves to move more freely.

P & S waves are the destructive duo that work to carry a vicious message to the surrounding areas. As the fault slipped near Amorgos in 1956, on the Amorgos fault, the P- and S-waves were shot up out of the crust and dispersed in different directions. This movement is close to the effect of dropping a rock in a water source, in the sense that the ripples radiate out in all directions.

The distance between Santorini and Amorgos is about 40 km (25 miles) which means that the seismic energy still had a great amount of power with little to no dissipation. The P-wave was the first to hit as it traveled quickly through the dense oceanic crust to reach its destination. This first wave gave the island this wake up call. As the S-wave hit the end of oceanic crust, it moved along the crust towards Santorini. Once it reached the island, it moved throughout the rock and shook the town in a side to side motion.

Due to the topography of Santorini, these P & S waves reverberated off the caldera walls, intensifying the shaking. The solid structure of the rocks caused the energy waves to bounce off the walls of the caldera like a tennis ball. This was unfortunate for Oia and Fira who were more susceptible to the damage due to the soft rock that they are built on. This is the reason why the majority of the damage occurred in these two towns.

Reverb
(Figure 4) Arrows in caldera show the concept of reverberation for P & S waves.

The earthquake of 1956 was a rare spectacle for the Aegean. The sea rarely experiences powerful earthquakes such as those that surround the Pacific Ocean. The island of Santorini was devastated by the 1956 earthquake and for those who remember the event, the danger is real. The Aegean is an unpredictable place. Thankfully due to modern architectural standard, i.e. reinforced concrete and steel arches, Santorini will be more prepared for the next big quake [1].

References:

  1. Friedrich, W. L., 2009, Santorini – volcano, natural history, mythology: Denmark, Narayana Press, 236-240 p.
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4 thoughts on “Devastation of the 1956 Earthquake”

  1. Micah – Great job and congrats on an amazing 3 weeks here. I think you’ve learned loads, struggled with finding your voice, and gained new interests.

    The figure on strike-slip faulting is choice…:-)

    Reverberation in the stiff caldera walls would actually cause the waves to refract and pinball back and forth within the walls themselves. I’m sure some reverberation also occurs between walls as you state as well (but remember S-waves won’t travel through the air).

  2. Hi Micah,

    This was a great informational post about earthquakes. A lot of this was familiar to me because of my Geological Disasters class several semesters ago so it was fairly easy for me to follow. However, you did a great job of explaining the information for an outside audience. You even took the time to explain the difference between P and S waves which really helps explain your post.

    I thought that the images you used were also very cool and worked really well with your post. They helped explain your concepts (Figure 2 with the sponges was super helpful!) and the history of the earthquake, (Figure 1 showing after the earthquake, and Figure 3 showing the island now).

    Overall, great job. This post was very well put together and it was a great way to wrap up your blog entries. Nice job!

  3. Hey Micah,

    Just sitting on the outskirts of the long valley caldera in my house and reading your post to try and wash away some post santo boredom vibes. Nice final publish btw, I needed a touch up on those different wave types. Also nice sponge example. And nice feature photo, it must have taken you a lot of effort to climb up that Mt. Profitis to take it! Hahah lol. 😉

    -Ray

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