Iran in particular hit by devastating quakes
Shifting Arabian plates mean tragic disasters are all too frequent for Middle East
The devastating 7.3-magnitude earthquake on the Iran-Iraq border that has killed hundreds is one of several similar events in recent years to have afflicted Iran in particular, causing huge loss of life.
The area’s location at the border of continental plates that are moving together and generating huge forces is behind the seismic activity, which in Sunday’s tremor killed seven people in Iraq and more than 340 in Iran.
The Arabian plate, which covers the Arabian peninsula, is moving northwards at about 3cm per year – approximately the rate at which human fingernails grow – and is bumping into the Eurasian plate, which covers a vast swathe of Europe and Asia. Where they collide the Zagros mountains have been formed and instability results.
“The collision zone runs all the way from eastern Turkey over to northern Iraq, southern Iran and across to Pakistan as well,” said Dr Stephen Hicks, a seismologist at the University of Southampton in the United Kingdom.
“This [northwards movement of the Arabian plate] is the origin of a lot of these earthquakes that have occurred in Iran especially.”
As the Arabian plate moves northwards, the plates “lock together” and absorb this movement, creating huge stresses.
“After probably hundreds of years in this case, that has to be released,” added Dr Hicks, a postdoctoral research fellow in passive source seismology.
Iran’s list of major earthquakes includes a pair in 2012, each with a magnitude of more than six, that struck in the north-west and resulted in more than 300 deaths.
At least 400 people were killed in 2005 by a 6.4-magnitude earthquake that hit the city of Zarand in the south-east. Most devastating in recent memory is another south-eastern tremor, the 2003 6.6-magnitude Bam earthquake, which left more than 26,000 dead.
The dividing line between the Arabian and Eurasian plates is shown on maps as a single boundary, but the reality is more complex, with there being many faults.
“It would be hard to gauge what the movement of these faults was over a long time,” said Dr Hicks.
The extent to which particular buildings are affected by a quake is “a complex interaction between the height of the building, how well the building is made and the rock it sits on”, said Dr Hicks.
Soft ground makes buildings more vulnerable, as has been shown in Mexico City both during the seismic activity in Mexico in September and the 1985 earthquake that killed thousands in the city.
The frequency of the tremor’s vibrations is also important, with high-frequency vibrations having more of an effect on lower-rise buildings, and low-frequency vibrations tending to affect taller structures.