Iran's vulnerability to earthquakes

One week on and there has been another big earthquake in Iran.

This latest tremor is centred on the remote and sparsely populated province of Sistan Baluchistan in the far south-east of the country, not far from the border with Pakistan.

Map

Early reports from international seismological organisations calculated a magnitude of 7.8 for the event and timed its occurrence at 10:44 GMT.

Iran is one of those regions of the world that is all too familiar with quakes, and has experienced some very big tremors in the past.

That said, you have to go back to September 1978 for one of comparable size.

Scientists will need time to pick through the data but in general terms, the big driver here is the clash between the Arabia and Eurasia tectonic plates.

The former is pushing north by a few centimetres a year.

In the west of the country, this compression leads to mountain building (the Zagros Mountains); but in the east something rather different is happening, with the Arabia plate diving under the Eurasia plate.

"The south-eastern coast of Iran and the southern coast of Pakistan form the Makran subduction zone," explained Barry Parsons, a professor of geodesy and geophysics at the University of Oxford, UK.

"The depth of the earthquake - current estimate 82km - and its location - 300km north of the coast - is consistent with this. However, its mechanism is normal faulting (extensional)," he told BBC News.

Last week's 6.3-magnitude quake in the west of country, close to Bandar Bushehr, resulted in 37 deaths.

The new one is bigger - about 180 times stronger in energy release compared with last Tuesday's tremor.

Early reports from the Iranian authorities suggested the casualties could be much higher this time. Deaths were certainly reported in neighbouring Pakistan.

Many factors play into the number casualties, including the time of day the tremor strikes and the quality of the buildings in the affected areas.

The worst quake in Iran in recent times was the Bam event in 2003. That was a magnitude 6.6 event that caused the deaths of some 30,000 people.

Major contributing factors to this appalling toll were the clay construction of much of the infrastructure in the city and the fact that the tremor struck in the middle of the night. Many people were caught in their beds.

The province of Sistan Baluchistan is one of the least developed and one of the poorest areas of Iran. It too will have inadequately engineered infrastructure. Fortunately, though, it is not a densely populated area of Iran.

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