With the south-east of Iran criss-crossed by a number of active fault lines, the possibility of another quake cannot be entirely discounted, whether or not it reaches the 6.3 degree magnitude on the Richter scale of that which flattened the ancient mud-brick city and its citadel.

"Since the December 26 earthquake, we have recorded nearly 80 major aftershocks in the region," said Mohammad Mokhtari, head of the Tehran seismology faculty.

In fact, there have been literally hundreds of aftershocks, most of them minor.

"In the last 24 hours, we have recorded 50 tremors, one of them in the night which measured more than three degrees," said Nourbakhsh Mirzaie from the seismological centre at Tehran university.

"In Kerman province, there are 18 active fault lines and the most active of them is the Nahbandan fault," according to Dastan Pour, professor at Kerman university, quoted by the IRNA news agency. "These faults will certainly move, but we just don't know exactly when."

In the past 25 years, Kerman and the south of the neighbouring Khorassan province have been hit by a dozen earthquakes measuring between 6.5 and 7.4.

The most devastating until now was that which struck southern Khorassan in September 1978, destroying the town of Tabass and killing around 25,000 people.

With the help the French university of Grenoble, some 20 portable seismic recorders have been set up in the region to monitor the activity of the fault which adjoins Bam and which, before the quake, was 15 kilometeres (10 miles) long.

"It is impossible to say if the Bam earthquake will activate the many other faults in the region, particularly the Gowk, or Golbaf, fault, which runs to the south of Kerman," a town with a population of 500,000, Mirzaie said.

There has been no movement in any of the other faults since December 26, he said. "But the ground is unpredictable. In theory, a large earthquake could activate the neighbouring faults."

Until the latest earthquake, Iranian seismologists were keeping a close watch on the Gowk fault, which they consider the most volatile and likely to move.

The fault has shifted three times since the early 1980s. "In 1981, two quakes of 6.7 and 7 degrees on the Richter scale hit the region in the space of 45 days, while in 1998, there was an earthquake of 6.6 degrees.

Medium-sized towns in the region like Rafsandjan, Baft and Shahr-e Babak are also built on the faults.

"But it is very difficult to predict at what moment these faults could move," Pour said. "Before December 26, Bam and the region had not known a major earthquake for a long time, which explains why the citadel of Bam, more than 2,000 years old, was still standing.

"But the fact that the faults are in the Earth's upper crust make the earthquakes even more destructive."

TERRA.WIRE