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Izmit (Kocaeli) Turkey Earthquake, August 17 1999, Set 2, Structural Damage
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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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