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On August 17, 1999, at 3:01 A.M. local time (00:01:39.8 UTC) a magnitude (Mw) 7.4
earthquake occurred along the westernmost North Anatolian fault. The earthquake epicenter
was 11 km (7 mi) southeast of the City of Izmit, in the sub-province of Kocaeli, a
densely populated area in the industrial heartland of Turkey, and less than 80 km
southeast of Istanbul.The Anatolian fault, a right lateral strike-slip fault, has
a history of earthquakes. (A right-lateral, strike-slip fault is one in which the
motion of the opposite side of the fault, as one looks across the fault, is to the
right.) In the last sixty years, there have been eleven earthquakes with magnitudes
(Ms) larger than 6.7 along this fault. The August 1999 quake was located in a seismic
gap between areas of the fault that had broken in 1967 and in 1963. The maximum displacement
along the fault was more than five meters. The total rupture length was nearly 170
km. Accelerograms showed that the earthquake consisted of two major events located
about 30 km apart.The earthquake damaged buildings across seven provinces for a distance
of 250 km from Istanbul to Bolu. As many as seventy percent of the buildings in portions
of the cities of Adapazari, Golcuk, Izmit, Topcular, and Kular were severely damaged
or collapsed. Nearly all the fatalities and injuries can be attributed to building
collapse. An estimated 60,000-115,000 buildings were damaged or destroyed. Damage
- estimates range from $10 billion to $40 billion. The fault crossed some of the most
densely populated regions of Turkey. The affected population numbered 15 million people.
Casualties totaled 17,000 and additional thousands were missing and presumed dead.
Injuries numbered 24,000 and 500,000 people were left homeless with 200,000 living
on the streets. The economics of the damaged region presented ten percent of the Gross
National Product of Turkey.Structural damage occurred in several ways. Many structures
were deformed or destroyed by the lateral and vertical offsets of the fault itself.
Several apartment buildings were torn apart by the fault rupture and collapsed. There
was great variation of response even among similarly constructed buildings in the
same neighborhood, with some collapsing and others having moderate or little apparent
damage. Residential buildings were usually three to seven stories in height. The predominant
structural type in Turkey consists of reinforced concrete frames with unreinforced
masonry infill (brick walls filling the gaps between concrete frames). These infill
walls tended to fall out with the earthquake shaking, adding stress to the beams and
columns.Failures occurred in foundations, and in soft stories. These are stories that
have few supporting walls and are often found in the first story of a structure. They
may be open stories in order to accommodate shops or a garage, and may have few walls
supporting the second story floor. Failures also occurred in weak columns paired with
strong beams, and in columns with lack of detailing and column confinement. Buildings
having four or more stories were much more likely to be damaged or to collapse since
the buildings with greater height incurred a greater amount of displacement at the
top relative to the bottom of the buildings. In some areas, buildings were subjected
to damaging ground settlement, liquefaction, or subsidence and inundation from lake
waters. Hundreds of buildings in the city of Adapazari settled, tipped, or toppled
as liquefaction weakened lakebed sediments. In the severe liquefaction areas, more
than sixty percent of multi-story buildings suffered partial or total collapse due
to structural failure. With the exception of the most heavily damaged areas, the water
system was functional in six days or less. There was no significant damage reported
to dams or reservoirs. Wastewater pipelines were heavily damaged. Electric power was
disrupted when buildings collapsed onto electrical lines, electrical poles tilted
or collapsed, and transformers tilted due to support failure. However, the electric
power service was nearly restored in two weeks. Some highway bridges were damaged
when fault rupture occurred beneath them. Only a few residential fires were reported,
since most building materials were fire-resistant, and there are no natural gas pipelines
in the region. Following the earthquake, fire broke out at the large Tupas Oil Refinery
in Korfez. One fire at the refinery resulted when a collapsed 90-meter reinforced
concrete stack knocked down equipment and pipeways. An oil spill from the refinery
contaminated the waters of Izmit Bay. Loss of electrical power, debris on the roads,
and lack of water hampered firefighting efforts. A number of damaging quakes have
occurred in this area in the past. In 1754, the area near Izmit experienced an earthquake
that resulted in 2,000 deaths. In 1967, a 7.1 magnitude earthquake occurred near Izmit.
In 1970, an earthquake near Gediz, 160 km (100 mi) to the south, killed 1,000 people.
This area of Turkey will continue to experience seismic activity. Appropriate steps
need to be taken now to minimize the effects and fatalities of the next earthquake.
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