It has witnessed some of Iran's most tumultuous events: the fall of the shah, the return of Ayatollah Khomeini and the transformation from pro-western monarchy to revolutionary Islamic republic.

Now Tehran's days as the Iranian capital appear numbered after a powerful state body approved a plan for a new principal city. The idea was proposed by the country's supreme leader, Ayatollah Ali Khamenei, and rubber-stamped by the expediency council.

Seismologists have warned that Tehran is liable to be struck by a catastrophic earthquake in the foreseeable future. It is not clear whether a new capital will be built from scratch or sited in an existing city.

Iran has had numerous capitals during its history, including Isfahan, Qazvin, Shiraz, Mashhad and Hamedan. Since the Qajar king Agha Mohammad Khan declared it capital in 1795, Tehran has become the country's political, social, economic and cultural centre.

Its infrastructure has been left creaking by rapid population growth that has seen it become home to 12 million people, up from 250,000 at the start of the 20th century.

A mass influx from the countryside under the last shah, Mohammad Reza Pahlavi, fed the social discontent unleashed by the 1979 Islamic revolution. The population has continued to spiral since then, with unregulated development creating a traffic-clogged and polluted urban sprawl.

Most recently, Tehran was the centre of mass street protests triggered by the disputed re-election of the president, Mahmoud Ahmadinejad, which opponents insist was achieved through fraud.

Plans for a new capital were first drawn up 20 years ago, but officials only gave them serious consideration after the 2003 earthquake that devastated the south-eastern city of Bam and killed an estimated 40,000 people. Experts warn that Tehran sits on at least 100 faultlines – including one nearly 60 miles long – and that many of its buildings would not survive a major quake.

Professor Bahram Akasheh, a seismologist and dean of the faculty of basic sciences at Tehran Azad University, said the city had been chosen as capital "by mistake" and its north-eastern suburbs were vulnerable to an earthquake measuring eight on the Richter scale.

"I warned of this 40 to 50 years ago and if they had listened to me then, Tehran wouldn't have grown into a macro-city, but now control is lost over it. The city is growing bigger and bigger every day and so are the poor suburbs around it," he told the Guardian.

He said a new capital should be built between Qom – home to the country's clerical establishment – and Delijan, in Markazi province, an area that has not seen an earthquake in 2,000 years.