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There was a suggestion that this earthquake occurred on the Bam fault, caused by the northward drift of the Arabian plate against the Eurasian plate.

The devastating earthquake at Bam, Iran, in 2003 was caused by the rupture of a rare, hidden fault that is invisible at the surface, experts say.

This fault runs directly under the city of Bam and, combined with the density of settlement, may have been responsible for the high death toll.

Blind thrust faults are buried under the uppermost layers of crust, but they cause the surface layers to fold over them as they deform, forming a tell-tale hill at the surface that identify them to scientists.

After the Bam earthquake, seismologists focused their attention on several known faults in the area with clearly visible surface traces that reveal their location.

The researchers used a technique called Interferometric Synthetic Aperture Radar interferometry (Insar) to map the deformation of the Earth's surface in images from the European Space Agency's Envisat satellite.

"The fault was right in the middle of the city. It was the combination of the large population so close to the fault that really caused the devastation at Bam.

"Even very recent buildings - less than 10 years old - were brought down by this earthquake because the shaking was so strong."

Hard shake

They discovered that the main rupture in the earthquake occurred on a fault to the west of those known from their obvious exterior features.

This previously unknown fault was not associated with any surface features. What is more, this blind fracture turned out to be a "strike-slip" fault, in which the blocks of crust move sideways relative to one another.

What Happened

A magnitude 6.6 quake struck the southeastern city of Bam on December 26, killing an estimated 43,000 people and destroying a 2,000 year-old fortress near the city.

Iranian authorities ended general search-and-rescue operations on Jan 2, 2004, despite the rescue of a 97-year-old Shahrbanoo Mazandarani after 8 days under the rubbles. On January 8, Thirteen days after being buried underneath earthquake rubble, a 56-year old man was found alive but in poor health in the southeastern Iranian city of Bam, an International Red Crescent spokesman said. Aid workers told Reuters the rescued man had travelled from a nearby village to Bam for medical treatment and was staying with his sister when the earthquake struck.

Relief workers from Iran and more than 60 countries have been trying to help tens of thousands of survivors who are homeless and without basic necessities.

Local people have told reporters that on the afternoon of the 25th of December there were some light tremors in the area but this would not be unusual for the region.

Friday is not a working day in Iran so many people came home for the weekend on the evening of Thursday the 25th of December.

At around 4am on Friday the 26th there was an earthquake, which shook houses. Some people got up and went out into the street but after a short period they returned to their beds. Then at 5.27am the second earthquake struck. It measure 6.6 on the Richter scale and the epicentre was the city of Bam.

Given the level of destruction it is probably safe to assume that the earthquake occurred close to the surface. Buildings collapsed. Roofs and ceilings tend to be made of many layers of bricks to keep the house cool in summer. These collapsed immediately burying tens of thousands of people under tons of rubble.

Comments

These notes are aimed at students studying for Edexcel (B) Unit 5 - Hazards, though will be suitable also for people studying with different exam boards and at different levels.

They were originally submitted by wackojacko in this thread on TSR Forums.