Izmit-Turkey EQ, Magnitude 7.4

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Posting Date: August 16, 1999, 4:02:00 PM

A major earthquake occurred yesterday, August 16, near Izmit, Turkey, some 56 miles east-southeast of Istanbul. The US Geological Survey (USGS) has issued a preliminary estimate of surface wave magnitude of 7.8 for the quake, and a preliminary moment magnitude of 7.3. The death toll stands at more than 1,000 and is expected to rise considerably. Thousands more are injured. Considerable damage was reported in the industrial city of Izmit and in the port city of Yalova, as well as in Istanbul. Many apartment buildings collapsed and an oil refinery in Izmit remains in flames. The naval base at Golcuk was also hard hit. While most mid- to high-rise buildings in Turkey are of reinforced concrete, construction practices tend to be poor and buildings are often not built to code. In addition, construction materials tend to be inferior, as there exist few quality control mechanisms. Most low-rise buildings, especially those in poorer areas, are of unreinforced masonry. According to the USGS, the earthquake occurred at a depth of roughly 10 kilometers, making this a shallow event and consequently more destructive than would be a deeper event of the same magnitude. The event took place along the westward extension of the North Anatolian fault system. The North Anatolian Fault marks the deforming zone between Turkey and Eurasia. In the past, large earthquakes have ruptured the whole 1,000 km length of this fault. The map below shows historical seismicity (events of magnitude 5.0 and greater) in the region. Preliminary estimates of magnitude are likely to be revised as more complete information comes in from seismic networks around the world. Indeed, there is currently some inconsistency between the two magnitudes, moment and surface, issued by the USGS. AIR will continue to monitor events in this area and will post additional information as necessary. AIR seismologists and structural engineers are currently developing an earthquake model for Turkey and several other southern European countries. Model release is scheduled for later this year.

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Posting Date: August 16, 1999, 4:02:00 PM