A major earthquake is likely to strike Istanbul over the next 30 years, killing thousands of people and collapsing as many as 50,000 buildings because of vulnerable construction, according to a team of engineers and scientists who recommend immediate action to protect the city.
"Based on recent seismic activity and the history of the North Anatolian fault south of Istanbul, there is definitely a very high probability that the city will be hit with a major earthquake over the next three decades," said Mete Sozen, Purdue's Kettelhut Distinguished Professor of Civil Engineering. "Istanbul is the economic and cultural center of Turkey, and there must be an organized effort to protect the city and its people."

Ersin Arioglu, a member of the Turkish parliament and an engineer; Polat Gulkan, an engineer and faculty member at Middle East Technical University; and Sozen provided recommendations to the Turkish government during their November presentation.

Upgrading buildings, bridges and other elements of the city's infrastructure would cost billions of dollars, and the Turkish government has begun preliminary steps to earmark funds for the project, Sozen said.

"We were gratified by the prime minister's understanding of the threat and his immediate call for effective action," he said.

Istanbul's population has grown from around 2 million in the mid-1960s to more than 12 million today. Many of the city's approximately 1 million structures do not conform to modern building standards. Multistory buildings stand side-by-side like an uneven patchwork, and floors often do not line up from one building to another, a flaw that increases the susceptibility of collapse during an earthquake. Builders often add stories to buildings that were not originally designed for the additional floors, also heightening the potential for collapse, said Sozen, an expert in designing reinforced-concrete structures to resist earthquakes.

About 12 percent of the city's buildings are "commercial mixed," meaning the ground floor is commercial and the upper floors are residential.

"These types of buildings are especially vulnerable to collapse because they have few walls on the ground floor to resist earthquakes," Sozen said.

City streets also should be widened because many are too narrow and would be obstructed with debris during a major quake, making emergency response difficult, if not impossible, he said.

The team of a dozen engineers and earth scientists reviewed seismic data and historical information during a five-day series of meetings in June, a gathering funded by the National Science Foundation and the Japan International Cooperation Agency. The group concluded that an earthquake with a magnitude of 6.8 to 7.5 is likely to strike the city within the next three decades.

"We think such an event could result in the collapse of approximately 50,000 buildings and the deaths of thousands of people," said Santiago Pujol, an assistant professor of civil engineering at Purdue.

The team recommended that Turkey create a central earthquake authority to oversee efforts to safeguard the city.

Buildings in earthquake-prone parts of the world should be constructed to endure the lateral forces exerted by the ground motion caused by temblors, Sozen said, and the likelihood of earthquakes makes Istanbul a poor location for certain kinds of construction.

A common flaw seen in buildings is referred to as "captive columns," where a wall is attached to a column but does not extend as high as the column, leaving a portion of the column unsupported.

"As a result, the unsupported portion of the column is very rigid and brittle so that earthquake forces concentrate too much on the column, causing it to break," Sozen said.

After one column breaks, the weight of the building is then concentrated on the remaining columns, causing them to break in succession and resulting in collapse.

Fifteen major earthquakes have hit Istanbul since the fourth century, with the last major quake in 1894. Two earthquakes struck about 80 kilometers (or 48 miles) east of the city in 1999, killing about 20,000 people in areas less populated than Istanbul and having similar types of buildings.

The North Anatolian fault is about 1,000 kilometers (600 miles) long and is located about 15 kilometers (9 miles) south of Istanbul at its closest proximity.

"It's like California's San Andreas fault, but it has been more active in the 20th century," said Ayhan Irfanoglu, an assistant professor of civil engineering at Purdue.

About two-thirds of the city's buildings are closest to the fault line in the southern part of Istanbul.

Protecting the city would require identifying the most vulnerable buildings and elements of the city's infrastructure, such as bridges and water-delivery systems, and upgrading all critical structures, such as schools and hospitals, to provide earthquake resistance. The engineers recommended that school buildings and hospitals be given priority for upgrading.

"There will be tremendous demands on the emergency response and hospital systems," Irfanoglu said. "We need to make sure that hospitals remain operational. Well-performing school buildings, besides the crucial fact that they would assure the safety of kids, could be used as shelters and emergency response centers after the earthquake."

Engineers also recommended that Turkey develop a communications system for emergency personnel that would function properly during such a catastrophe. Another critical need is to develop an educational program for construction and engineering professionals detailing how to retrofit and properly design buildings to resist the stresses imposed by earthquakes.
ScienceDaily (Jan. 9, 2006)

http://www.sciencedaily.com/releases/2006/09/060908171606.htm