20 April 2012

Geological Data Suggest Greek Region Is Vulnerable To Tsunami Events

A tsunami is usually thought to be one giant wave. In actuality, it is a series of water waves, each bigger than the previous one. It is caused by the displacement of a large volume of a body of water, typically an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.

On 26 December 2004, a devastating tsunami up to 98 feet high, hit the northern province Aceh of the island Sumatra. It is estimated that 230,000 people were killed.

Recently in Japan on 11 March 2011, a tsunami hit Miyako in Tōhoku's Iwate Prefecture. The tsunami which reached a height of 133 feet, caused a number of nuclear accidents, primarily the ongoing level 7 meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. The confirmed death toll was at 15,840.

The largest recorded tsunami was a wave 1720 feet tall in Lituya Bay, Alaska on 09 July 1958. Millions of trees were uprooted along the bay but no casualties were reported.

Warning signs from ancient Greek tsunami

In the winter of 479 B.C., a tsunami was the savior of Potidaea, drowning hundreds of Persian invaders as they lay siege to the ancient Greek village. New geological evidence suggests that the region may still be vulnerable to tsunami events, according to Klaus Reicherter of Aachen University in Germany and his colleagues.

Video: What is a Tsunami

The Greek historian Herodotus described the strange retreat of the tide and massive waves at Potidaea, making his account the first description of a historical tsunami. Reicherter and colleagues have added to the story by sampling sediments on the Possidi peninsula in northern Greece where Potidaea (and its modern counterpart, Nea Potidea) is located. The sediment cores show signs of "high-energy" marine events like significant waves, and excavations in the suburbs of the nearby ancient city of Mende have uncovered a high-energy level dated to the 5th century B.C. The Mende layer contains much older marine seashells that were probably scoured from the ocean bed and deposited during a tsunami.

This figure shows the excavation area at Mende; the yellow box shows location of section.

Earthquake forecast modeling in the North Aegean Basin near the peninsula suggests that future earthquakes in the area could produce significant tsunami waves, although the area is not included currently in the ten "tsunami" prone regions of Greece. However, Reicherter and colleagues say their new findings suggest the Thermaikos Gulf where the peninsula is located should be included in tsunami hazard calculations, especially since the area is densely populated and home to many holiday resorts.

Reicherter presented his findings at the Annual Meeting of the Seismological Society of America (SSA) in San Diego.


Seismological Society of America
Aachen University
The Science and Physics of Earthquake Prediction
Earthquake Watch
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