But the proposal is receiving renewed attention after more than 30,000 people died in last month's 6.8 earthquake in Bam, in southeastern Iran.
The head of the Supreme National Security Council has raised the issue, and the rapporteur of the parliament's National Security and Foreign Policy Committee has said parliament is prepared to pass an urgent plan to change the site of the capital, home to some 12 million people.
Iran is among the most earthquake-prone countries in the world, and experts say it's only a matter of time until a major tremor strikes Tehran.
Manuel Berberian is a senior seismologist who published the first complete study on the seismology of Tehran some 20 years ago. He says the likelihood of a major earthquake hitting Tehran is great. "[My colleagues and I] have clearly mentioned there [in the report] that the city, as well as the [city of] Ray to the south, has been devastated by several earthquakes, and the city itself is located by the North Tehran Fault, which is to the north, and several faults to the south, as well numerous faults crisscrossing the city," he said, "So we know the hazard of the city, but we cannot predict the time of the earthquake."
Tehran experienced its last major earthquake in 1830, when an estimated 45,000 people were killed. Experts say the fault lines around Tehran have been slipping and gathering energy ever since.
The probability of an earthquake above 7 on the Richter scale hitting Tehran in the next 10 years currently stands at around 65 percent. That's according to the head of the International Seismographic Research Center of Iran's Ministry of Science.
Bahram Akasheh, a professor of geophysics at Tehran University, also agrees that the probability of a strong earthquake hitting Tehran in the near future is high. "Based on the earthquakes that have occurred in the region of Greater Tehran, and also based on historical earthquakes we've had in this region, I have estimated that the possibility of an earthquake measuring more than 6 on the Richter scale occurring now in Tehran is about 90 percent, and the possibility of an earthquake measuring more than 7 is about 60 percent," Akasheh said. "But these are mathematical estimates, and the complications of geology and seismology do not let us exactly know whether these estimates are correct or not."
Tehran would be devastated by a major earthquake. According to a study by the Japanese International Cooperation Agency, 80 percent of the buildings in some of Tehran's districts would be destroyed. According to Iranian newspapers, the destruction would likely include most public buildings.
"An earthquake in Tehran would have millions of victims," wrote the "Shargh" newspaper. "Only five out of 32 fire stations in Tehran are earthquake-proof. So the same people who are supposed to rescue us at the time of the disaster will be devoured by it."
Another newspaper, "Aftabe Yazd," cites the Health Ministry as estimating that an earthquake measuring 7 on the Richter scale would destroy 90 percent of the city's hospitals.
Berberian, the seismologist, compares an earthquake in Tehran with the catastrophic earthquake that struck the city of Tangshan in northern China on 26 July 1976. In the 1976 earthquake in Tangshan, approximately half a million people were killed, he says. "For Tehran, with 12 million-plus population, heaven knows. It's easy to guess, but it is scary," he said. "I don't want to think about that."
Professor Akasheh also says a major earthquake in Tehran would have tragic consequences. "Because the buildings are not [earthquake] resistant, the human and financial costs [of earthquakes in Iran] are very heavy," he said. "Regarding Tehran, because the population of Greater Tehran is more than 15 million, and all the buildings are built on unstable ground, we have to expect heavy destruction from an earthquake measuring 7 on the Richter scale -- devastation that would be irreparable."
He continued, "If a similar earthquake [to the one in Bam] happens in the Tehran region, the city itself will probably top the death toll list [of earthquakes] in the world."
While experts agree on the danger, they differ on how to respond to it.
Iran's Supreme National Security Council and some members of parliament are in favor of moving the city to safer ground. Countries have moved their capitals before. After reunification, Germany moved its capital from Bonn to Berlin. In the late 1990s, Kazakhstan moved its capital from Almaty to Astana, in part because of its location in an earthquake-prone area.
But other officials, such as the mayor of Tehran, disagree, saying that moving the capital, at least quickly, would only secure the safety of top officials.
Professor Akasheh says he's written to President Mohammad Khatami, recommending the capital be moved to a safer place, such as the city of Isfahan in central Iran, which was the capital until the late 18th century. Even if the process is long and costly, he feels it's the best solution.
"The moving of the capital is not something that can be done in a year or two," he said. "We need 20 to 30 years for gradually moving the population out of the capital. We can't move the capital in one night. This needs a lot of time and a huge budget, but we shouldn't allow ourselves to be caught off-guard against a fait accompli, that in one night during 10 to 20 seconds Tehran will be turned to zero."
But Berberian disagrees, pointing to the earthquake risk in Iran's other major cities. "I doubt it because, first of all, it's very difficult and expensive," he said. "And second is that, what about the other cities -- provincial capitals like Tabriz, Mashahd, Shiraz, and so forth? I mean, the whole country is seismic."
Berberian says engineering codes should be enforced and buildings, especially public buildings, should be made safe.
Akasheh, however, says it's impossible to make all of Tehran's buildings earthquake-resistant. "In my opinion, making buildings in Tehran resistant is impossible," he said. "First of all, we have to make the buildings of the leadership resistant, then the government buildings, then the museums, the hospitals -- and this process [for a city such as Tehran] is impossible. How do we want to do it in streets with widths of only 5 meters, and where there are buildings with several floors?"
Berberian maintains that since Iran is prone to earthquakes, it should learn how to prevent such disasters, as Japan and the United States have done. "It's not easy and it's not cheap, but moving cities will not resolve the issue," he said. "We have this problem [of frequent earthquakes]. We know the sources of seismicity, which are the earthquake faults. We have to learn how to live with earthquakes. That's the only thing we haven't learned yet."
Iran says some steps have already been taken, such as securing natural-gas pipeline networks. But a government spokesman, Abdollah Ramezanzadeh, said there's "still a long way to go to make Tehran a safe place to live."
Meanwhile, the head of Iran's Supreme National Security Council, Hassan Rowhani, says the council will update its 1991 proposal on moving the capital and submit it for consideration by March.