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Istanbul, Turkey
Lamont-Doherty marine geologists and seismologists work to more accurately forecast near-shore earthquakes
On August 17, 1999, an earthquake of magnitude 7.4 hit northwest Turkey, killing more than 17,000 people, injuring more than 40,000 and causing damage in the tens of billions of dollars. To seismologists, the location of the Kocaeli earthquake was not surprising: the event occurred on the North Anatolian Fault which, like California’s San Andreas, is highly active and produces a constant stream of seismicity. To civil engineers, the amount and type of damage to critical buildings also was not surprising. The type of residential and commercial construction prevalent in many cities in developing and transitional countries is easily damaged by the shaking motions of even moderate earthquakes.
After the disaster, Lamont-Doherty seismologists Leonardo Seeber and John Armbruster traveled to the earthquake zone to deploy an aftershock monitoring network in collaboration with Turkish colleagues. An important question that was addressed by this study is whether the tectonic stress released during the Kocaeli earthquake creates new stress conditions on the North Anatolian Fault that could accelerate stress buildup and advance the timing of the next earthquake. The unfortunate reality is that the next segment of the fault due to rupture is located directly south of Istanbul, in the Marmara Sea.
Istanbul has been struck by many large earthquakes during its history, but no damaging events have occurred during modern times. A large earthquake in the Sea of Marmara would be devastating not only to Istanbul, but to the Turkish economy more generally. Earthquakes cannot be prevented, but damage from them can be reduced by careful planning and adherence to modern construction guidelines. The question is: can reasonable risk reduction be accomplished within the physical, economic and social constraints present in modern-day Turkey?
The first order of business is to identify unambiguously the precise segment of the NAF expected to rupture near Istanbul. This is hard for geologists to do because the segment is under water in the Marmara Sea. Lamont-Doherty marine geologists Mike Steckler, Milene Cormier, Bill Ryan, working with seismologist Seeber, have developed a marine surveying technique that can in principle identify the subtle distortions of soft underwater sediments that occur when earthquakes rupture the harder rock of the crust below. This is called “marine paleoseismology,” and, if successful, could provide much more accurate forecasts of the occurrence of near-shore earthquakes. Together with Turkish partners, the Lamont team has been funded by the U.S. National Science Foundation to survey the Sea of Marmara to try to detect the occurrence of historic large earthquakes, and thus define the active segment of the NAF. This cruise is scheduled to take place on Lamont’s ship, the R/V Langseth, in 2007 or 2008.
Once the fault segment is identified and located, it becomes possible to construct earthquake scenarios that can be used by civil engineers to predict potential damage. Andrew Smyth and George Deodatis of Columbia's Department of Civil Engineering and Engineering Mechanics have been developing structural modeling tools that can be used to predict the response of typical buildings to various levels of earthquake ground shaking. Using this approach, Smyth, Deodatis and their Turkish colleagues were able to demonstrate that residential apartment buildings of the sort common throughout Istanbul can be retrofitted inexpensively, a result used by economists in cost-benefit models.
The integrated approach needed to develop earthquake hazard reduction strategies is a characteristic of the international, interdisciplinary studies common at Lamont, and can be extended to other geological and meteorological hazards.
Contact
Arthur L. Lerner-Lam
Doherty Senior Research Scientist
Lamont-Doherty Earth Observatory
Seismology Geology and Tectonophysics
61 Route 9W - PO Box 1000
Palisades, NY 10964-8000
Email: lerner@ldeo.columbia.edu
Tel: +1 845-365-8356
Fax: +1 845-365-8150
Structural failure, 1999 Izmit, Turkey earthquake.
Courtesy of John Wallace, NEES@UCLA Laboratory for Field Testing & Monitoring, UCLA Structural/Earthquake Engineering Research Laboratory
“Pancake” collapse of a concrete apartment building in Goliaka, Turkey, resulting from the 1999 Kocaeli earthquake.
Courtesy of Nano Seeber, Lamont-Doherty
The Marmara Sea and the proposed location of survey sites and instrumentation. Fault segments are shown in red.
A virtual representation of a five-story apartment building in the Caddebostan section of Istanbul in a structural response program developed by Smyth and Deodatis. By “shaking” the building in the computer, engineers can efficiently design cost-effective strategies for strengthening the structure.
