1999 Izmit, Turkey Earthquake
The magnitude 7.6 earthquake that struck western Turkey on August 17, 1999 (also known as the Kocaeli, Turkey, earthquake) occurred on one of the world's longest and best studied strike-slip (horizontal motion) faults: the east-west trending North Anatolian fault. Maps of Turkey and California show how that the North Anatolian and San Andreas faults are very similar. This fault is very similar to the San Andreas fault in California. This similarity has lead to active scientific collaborations between scientists in Turkey and the US aimed at understanding the hazards we both face. A comprehensive U.S.G.S. report about this earthquake, its effects, and its implications for future hazard in both Turkey and the United States is available on line (pdf format, 6MB).
Turkey has had a long history of large earthquakes that often occur in progressive adjacent earthquakes. Starting in 1939, the North Anatolian fault produced a sequence of major earthquakes, of which the 1999 event is the 11th with a magnitude greater than or equal to 6.7. Starting with the 1939 event in western Turkey, the earthquake locations have moved both eastward and westward. The westward migration was particularly active and ruptured 600 km of contiguous fault between 1939 and 1944. This westward propagation of earthquakes then slowed and ruptured an additional adjacent 100 km of fault in events in 1957 and 1967, with separated activity further west during 1963 and 1964.
The August 17, 1999 event fills in a 100 to 150 km long gap between the 1967 event and the 1963 and 1964 events. This gap was first noted by Toksoz, Shakal, and Michael in 1979 and it's hazard was later analyzed by Stein, Barka, and Dieterich in 1997. The latter paper estimated that there was a 12% chance of this earthquake occurring in the 30 years from 1996 to 2026.
An international team of scientists and engineers is currently mapping the earthquake rupture and its effects, using a wide variety of techniques from visual observations, to seismology and geodesy. This team includes scientists and engineers from the USGS, invited by our Turkish colleauges.
On these pages we will post news sent back by the USGS team and links to other resources. We hope the reports and images on these pages will give you an insider's view into the scientific investigative process as it unfolds in Turkey.
The data collected will be used to better understand how the buildings failed in the earthquake. Of particular interest in the earliest stages of the team's work are the types of structural failure that occurred, and the kinds of construction practice that were employed in the failed and surviving buildings. The observations need to be made quickly, before the rubble is cleared away. Analysis of the data can indicate which building practices were successful, which were not, and how the local soil conditions under the building may have affected the shaking and ground failure there.
In some areas, such as this one in the town of Golcuk, 60 miles east of Istanbul, the contrast in structural performance can be striking, with this very old mosque outperforming more modern buildings surrounding it. By learning from the failures, improved construction practices and codes may save lives in future earthquakes.