Earthquakes on Crete?

Since many people ask us about the chance of having an earthquake on Crete, we here will try to explain the geological situation. The questions came after the earthquakes in Turkey and Athens/ Greece, August and September and November 1999.

First of all we like to make clear that in the past decades there have been NO earthquakes on Crete that have caused serious damage. The last big earthquake in 1953 nevertheless caused major damage across Greece, and triggered big social changes due to emigration following loss of life and property etc. It is one reason why, in some areas, there are no old houses left.
On March 18, 1953 the major Yenice-Gonen earthquake strikes West Turkey, and 250 people die. On the Ionian islands it destroyed most buildings on Zakynthos and the nearby island of Cephalonia, with 7,2 on Richter's scale. More than 476 people were killed. It is said that this earthquake affected Crete also, with for instance some damage to the water cisterns in Loutro and some roofs collapsing.

But earthquakes do happen sometimes on Crete.
"As been mentioned Crete is an 'active' area with small earthquakes every year. The last significant earthquake was about 5 years ago [1994], 6,3R as I remember. I was standing on my patio at the time and suddenly instead of standing on concrete I felt that I had jumped onto a bed. I had water in bowls (for the cats) and this started sloshing from side to side, spilling out of the bowls. A little later I visited an office on the 5th floor of a block in Chania where there was a free standing iron decorative stand against a wall and I could see marks on the wall where it had swayed from side to side about 10cm or so. However, there were no reports of severe structural damage, just odd bricks and tiles in the road from the tops of old buildings, and a few old garden walls down. I remember at the time feeling that there was less damage than happened a few years previously in England when there was a hurricane.
One must remember that the Richter scale is based upon energy released and this is not always a good indication of 'effect'. An structural engineer friend said that the Turkish eathquake was very long in duration as these things go although the R value was not too high. The earthquake in Athens was only 5.9 but it was very fast moving which exagerated its impact.
The building regulations in Greece are very strict with respect to Earthquake resistance: Accoring to my friend amongst the most stringent in the world. To obtain planning permission you must supply a complete structural 'static' analysis of the foundations and skeleton to show that it will withstand earthquakes. All factors are specified in the plans, the sizes of columns etc, the steel and Grade of concrete are all specified. The problem is that the building must be constructed according to the design and with good building practices. For instance the owner, or the builder may decide to save money by perhaps using less steel or by using a lower strength grade of cement, or may not excavate enough to ensure solid foundations. The builder may add water to the specified mix of concrete to make it easier to work, he may not place the steel correctly within the concrete formwork, he may not 'cure' the cement properly (keeping it wet during the setting time, perhaps 5 days). These things should be checked by the engineer responsible for the building, but ... I believe that in Athens the Architects/Engineers and builders responsible for the construction of the buildings that collapsed are currently being sought. Perhaps we shall learn more.
Of course quite a number of people decide to build without obtaining planning permission, but that's another story. Another problem, particularly with commercial buildings, is that the owners may decide to modify them when business need change, perhaps without consulting an Engineer to question the impact of the changes. With respect to the steel often seen protruding from the tops of buildings, as I think someone else has said, the Greeks are very family oritented, when they build they do often plan for further stories for their children eventually. If they can afford it they build beforehand and rent-out the upper floors, always intending their children to eventually live there. Well built old houses often resist earthquakes but in a completely different way than new buildings. Problems arise when they are not properly maintained or are 'renovated' in a 'modern' way using large quantities of concrete which tends to work against their intrinsic resistance modes."

The map is almost self-explanatory. South of the Islet of Gavdos, following the South coast of Crete, is 2400 meters deep in the Libyan Sea the break line or trench of Ptolemeus.

We can't remember the source of this image.