Istanbul: Does the city threaten a multiple quake?

Computer simulation examines movement rates of the Northeast Anatolian Fault

Istanbul © Josep Renalias / CC-by-sa 3.0
Read out

Istanbul is extremely earthquake-prone, because it is close to the Northeast Anatolian Fault. Earthquake researchers expect the next major quake of this disruption immediately south of the city. A new computer study published in "Nature Geoscience" now shows that the tensions in this part of the fault could also be discharged in several earthquakes rather than a single major earthquake event.

When the earth shook in August 1999 in Izmit, Turkey, the disaster claimed 18, 000 lives and destroyed large parts of the city. But the earthquake with a magnitude of 7.4 was not an isolated case, on the contrary: it was just the latest quake of a series that began in 1939 in eastern Turkey. Successively, they brought the plate boundary between the Anatolian and Eurasian plates west to Izmit 1999 to failure. South of Istanbul, however, the chain of earthquakes along the North Anatolian Fault still has a gap. The next quake in this series is therefore expected by seismologists right there.

Movement rates of the fault analyzed

How big is the earthquake risk for the Turkish city? An important factor for assessing the seismic hazard are the rates of movement of tectonic disturbances. Tobias Hergert from the Karlsruhe Institute of Technology and Oliver Heidbach from the GFZ German Research Center for Geosciences now present the results of a computer simulation that analyzed the movement rates of the North Anatolian Fault. The study was created as part of the project Megacity Istanbul by CEDIM (Center for Disaster Management and Risk Reduction Technology).

Hergert and Heidbach divided the area into 640, 000 elements in order to determine the kinematics of the fault system three-dimensionally. "The model results show that the movement rates at the main disturbance are between ten and 45 percent lower than previously assumed, " explains Heidbach. "In addition, the movement rates vary by 40 percent along the main fault."

Discharge possible in several quakes

The scientists interpret this variability as an indication that the built-up voltage in the earth's crust can discharge into two or three smaller-magnitude earthquakes instead of a single tremendous earthquake. However, an all-clear for Istanbul does not mean this: the seismologists expressly point out that the short distance of the main fault to Istanbul still represents an extreme earthquake risk for the mega-city. The fault zone is less than 20 kilometers from the city limits. In addition, even these smaller quakes may be larger than magnitude 7; Prevention of the occurrence of a quake is therefore essential. display

(Helmholtz Center Potsdam GFZ German Research Center for Geosciences, 20.01.2010 - NPO)