NEWS

US vessel maps Greek fault lines

In a country often described as sitting on a plate of broken glass, the sailing of a US seismology vessel into Greek waters was bound to run into choppy seas. Columbia University’s Maurice Ewing was charting the submarine swathes of the Gulf of Corinth just as a 5.7-Richter quake hit the central Aegean island of Skyros some 200 km east of the gulf this summer, damaging scores of buildings. That was just a gentle reminder, joked University of Hawaii Professor Brian Taylor. Other tremors shook the western city of Patras and the Ionian island of Zakynthos, sending Greeks into the streets two years after a strong quake in Athens killed 143 people. Undaunted during its 10-day mission to Greece, the Ewing unreeled its six-km-long (3.75 mile) hydrophone cable to chart the depths of the sea and pinpoint potential crust faults. Its sound guns, 20 air-popping glass and metal tubes attached to the stern, shot air into the depths of the Corinthian Gulf every few seconds. Greece is not just a jigsaw puzzle of faults and crusts, it also sits on the daunting north Anatolian fault system. This vast and evolving fault stretches for thousands of miles from the depths of eastern Turkey, through the sea of Marmara and down into the central Aegean before ending abruptly in mainland Greece. The next tremor Greek seismologists are looking at the Ewing for clues on when and where the next tremor will strike. We’re not in the business of earthquake prediction, we don’t believe it’s realizable, said Michael Purdy, director of Columbia’s Lamont-Doherty Earth Observatory. But he still thinks earthquakes are worth talking about. If we are to make progress, we should coordinate and collaborate, Purdy told an audience of Turkish, Italian and Greek colleagues, as his vessel, carrying dozens of scientists and technicians, docked in the port of Piraeus. Several prominent Greek seismologists attacked each other’s views on quakes. Some predicted future tremors, causing public concern. But the Ewing’s clear-headed and pedantic marine survey is expected to provide tangible information on the historic gulf’s faults. We have imaged the faults in the upper crust, where they occur and how they link, or don’t link, to known faults on land, Taylor told reporters. At a speed of just five knots an hour, the Ewing fired its sound guns, patiently mapping the seabed which emerged in multicolor printouts, on computer screens and plotters in the vessel’s nerve center, the high-tech instrument room. We could say these guns are a highly advanced sonar, sending a signal into the water and waiting to get an echo back which will give us information on the seabed, said a scientist on board the ship. He said the data will take more than 12 months to process but is expected to show the distribution of faults at depths of 5-15 km, the point where major earthquakes occur. Working together Greek seismologists, eager to get their hands on such information, were quick to join scientists on the Ewing. We never had data using cable of such length – this is very useful for us as it gets information from much, much deeper, said Athens’s National Observatory seismologist Maria Sachpazi. As part of their visit to Greece, the US scientists joined other colleagues in the northern city of Thessaloniki to discuss the Anatolian fault – many times more lethal than the spider web fault plan of the Corinthian Gulf. Greece and Turkey share a long history of destructive earthquakes that are due to this fault. The latest tremors in northwestern Turkey in 1999, measuring 7.4 and 7.2 on the Richter scale, killed more than 18,000 people. This system and its related secondary faults… are the most significant source of earthquake hazard in the region, said Aristotle University of Thessaloniki geophysics professor Eleftheria Papadimitriou, who urged her colleagues to start joint projects to study the fault. Other scientists agreed recent ruptures in the fault’s system heightened the risk of destructive quakes in the next 30 years and increased the need for joint research. We suggest the establishment of an Internet-based Northern Aegean and Marmara Earthquake Information Network, said Naci Gorur, coordinator of Marine Research at Turkey’s Scientific and Technical Research Council. For once, Greeks and Turks, traditionally at odds over a series of political issues, seemed to agree.