Earthquakes in the Eastern Mediterranean? Much More Plentiful in Past Than Thought

There is more seismic activity in the eastern Mediterranean than was previously thought, and a study about this was recently accepted for publication in the journal Geophysical Research Letters.

Historically in the long stretch of geological time, seismic activity near and around Crete has stirred up bursts of earthquakes, and this may increase the region's future risk of earthquakes and tsunamis, according to a release.

Several tectonic plates are in the Mediterranean basin, caused by the African and Eurasian Plates crashing together there. While scientists have been aware that the collision between the two plates can make the eastern part of that sea and land area susceptible to earthquakes, they've also been confused by the region having gone through only two (known) earthquakes larger than 8 on the Richter scale in 4,000 years.

The African Plate goes under the Aegean microplate just south of Crete. This occurs in an area shaped like an arc, which is called the Hellenic margin. The scientists in the study looked at the history of earthquakes in this subduction zone, to learn what could drive mega-earthquakes in the area.

"We study the Hellenic subduction margin going back to about 50,000 years, which is about 10 times the time window of paleo-earthquake observations in the eastern Mediterranean that we had before," Vasiliki Mouslopoulou, at the GFZ German Research Center for Geosciences, and study lead author, in the release. "For the first time ever, we were able to chart the spatial and temporal pattern with which mega-earthquakes rupture the Hellenic margin."

The study included field studies and radiometric dating (used to date materials such as carbon), as well as numerical models for part of the Hellenic margin crossing Crete. Today the Crete shorelines in question are about 75 feet above sea level. The scientists also found signs of previous shorelines, which are believed to show the sea level at the time at which they occurred. They also indicate, with their altitude in relation to sea level, the entire vertical movement that occurred as a result of earthquake motion. 

The scientists learned that in the past 50,000 years, western and eastern Crete have both moved about 328 feet above sea level, lifted there by a minimum of 40 earthquakes measuring greater than 8. The quakes arrived from offshore, starting in three seismic faults along the Hellenic margin's western and eastern parts.

There have been so many big earthquakes in this area that figuring out when they'll occur again is a challenge, the study's authors said in the release. But the scientists noted that tsunami early warning systems and construction suitable for earthquakes is important to consider, in terms of the now-known increased risk.

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