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Anastasia Balezdrova

For 24 hours now humanity has been following the destruction, caused by the earthquake and the subsequent disastrous tsunami in Japan. Greece is a country with high seismicity and many people wondered whether it was possible for the quake, which happened at a distance of thousands of miles to “wake the sleeping outbreaks”. GRReporter sought a response from Konstantinos Papazahos, a geophysics professor at the Aristotle University of Thessaloniki.

Would you describe the earthquake in Japan?

This was an earthquake with a magnitude of about 9 on the Richter scale that happened along a very famous tectonic fault. It is located between the Pacific Ocean plate and small Japanese plate. The Pacific ocean plate slid under the Japanese in the length of thousands of kilometers.

The primary effects of the earthquake, although serious are not threatening. Human casualties and material damages were caused by the tsunami that followed. It was initiated by the rapid lifting by few meters of the seabed in the area, causing movement of the sea water and it appeared on the surface in the form of gravitational wave, the so-called tsunami.

How long can secondary quakes continue?

Secondery quakes will continue for many months. Practically we’re talking about years. Quakes will be of high magnitude and it won’t be strange if one of them reaches 7.5 to 8 on the Richter scale.

Apart from these minor earthquakes and because they occur in a tectonic zone it is very likely that induced earthquakes also occur, ie quakes caused by this earthquake in areas adjacent to this zone. They may be to the northeast towards the Kurili, Aleutian Islands and Alaska or southwest towards the rest of the Japanese arc and Philippine Islands.

What's 'domino effect'?

It is this phenomenon which I've described just now. The term "domino" is an unscientific term used to describe that an earthquake that happened in a specific place can cause lacerations in the contiguous areas and generation of strong earthquakes. However, this applies to the northwestern Pacific Ocean, where this earthquake happened, not to the entire planet.

I.e. you think this activity can not affect Greece, which is anyway a pretty seismic zone.

There is no way, no mechanism, statistical probability or geophysical model that provides something like that. Practically the possibility for the Greek seismicity to be affected is zero.

Nevertheless, the tsunami's formation is not something strange for Greece. In 1956 a wave like this swept the island of Amorgos. Tell us about this.

First I want to say that there were tsunamis in the Aegean in different periods. Simply the wave in 1956 was one of the most impressive ones, which we remember because it was part the earthquake in Amorgos and had a height of 25 meters.

But in other earthquakes as well, such as the one in 1932 in Yerisos on the Halkidiki peninsula thre was a great tsunami of height for some meters. Not to mention the earthquake in 365 AD in the western Crete, when the tsunami caused huge damage also in Egypt, on the shores of Palestine and Israel, but also serious problems to Venice.

Therefore, these waves are not unknown in the eastern Mediterranean and Aegean. In any case, however, they are considerably smaller. This is due to the fact that earthquakes that occur in Greece are of much smaller scale. The earthquake in Amorgos was a very rare case. In the small bays of the Aegean and in the open sea are formed  tsunamis that cause damages, but this happens within very large periods of time. Quakes that occur outside of the Hellenic Arc south of Crete, the Peloponnese and Rhodes cause tsunamis that affect the coasts of Africa or the shores of Palestine, Israel and Lebanon.

So a tsunami of a far smaller scale and very large periods of time. The main threat to Greece are the earthquakes that are of average magnitude of 6 to 6.3 on the Richter scale and occur almost every year. This means that in one year there may be no earthquake in the next year to occur two and in the third to have a stronger earthquake. When these earthquakes occur in areas near the coast they cause damages. The good news is that most earthquakes happen at the sea. If I tell you that south of Crete there was an earthquake measuring 6.2 on the Richter scale last year you won’t even remember it because it happened far from land and did not have any consequences.

We all, however, remember the earthquake in Athens in 1999 with magnitude 5.9, which was the most disastrous in the Greek history. Therefore, the problems here are caused by seismic vibrations, not by tsunamis.