USGS adjusts the magnitude of Turkey earthquake

August 18, 1999

On the basis of additional data, the U.S. Geological Survey (USGS) has updated the magnitude of the destructive earthquake that struck western Turkey early Tuesday, to 7.4. The initial preliminary magnitude of 7.8, was based on recordings of seismic waves from a limited number of global stations that rapidly transmit data to the U.S. Geological Survey's National Earthquake Information Center (NEIC) in Golden, Colo.

Scientists at the NEIC have since received additional data that permit a more accurate determination of the earthquake's location, magnitude, and depth.

The Izmit earthquake occurred at 00:01:39.80 UTC (3:01 a.m. local time), and was centered at at 40.702 N., 29.987 E., which places the epicenter about 11 kilometers, or seven miles, southeast of the city of Izmit. This location indicates that the earthquake occurred on the northernmost strand of the North Anatolian fault system. The earthquake originated at a depth of 17 kilometers, or about 10.5 miles, and caused right-lateral strike-slip movement on the fault. Preliminary field reports confirm this type of motion on the fault, and initial field observations indicate that the earthquake produced at least 60 kilometers (37 miles) of surface rupture and right-lateral offsets as large as 2.7 meters (1.6 miles) or almost nine feet.

Additional field studies by U.S. and Turkish scientists will refine details of the geological effects and seismological parameters of this major earthquake.

As the nation's largest water, earth and biological science, and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation and the economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.
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