While rescue teams sift through the rubble, experts said many factors explained the difference between the approximately 700 dead so far in Chile while the grim tally in Haiti has topped 220,000.

An earthquake's magnitude reflects the amount of seismic energy released at its epicentre, usually the meeting point of tectonic plates pushing up against or pulling away from each other.

The Haiti quake, which struck on January 12, measured 7.0 in magnitude, while the one in Chile, at 8.8, was nearly two orders of magnitude greater.

Each notch on the scale represents a 10-fold increase in amplitude, or the degree of shaking of the ground, and a more than 30-fold jump in the amount of energy released.

"But there is no direct link between magnitude and its deadliness or level of destruction of human habitat," said Robin Lacassin, a seismologist at the Institut Physique de Globe in Paris.

Some 15 to 20 quakes every year top magnitude 7.0, but most of them go unnoticed except by scientists because they occur in the ocean or unpopulated areas.

Both recent quakes occured near large cities, so other factors account for the difference.

"The earthquake near Port au Prince was very shallow, only about 15 kilometers (nine miles) below the surface," compared to about 35 kilometers (22.5 miles) below the ocean floor for Chile, Lacassin said.

But proximity alone did not account for the massive destruction of huge loss of life in January, he and other experts pointed out.

"The quality of construction and building codes in Haiti were obviously not as strong as those in Chile," said David Galloway, a seismologist at the British Geological Survey.

The region along the western coast of South America has been hit several times before by major quakes, including the largest on record -- a monster in 1960 measuring 9.5 on the Richter Scale -- very near by.

"Chile knows earthquakes. Their codes are more stringent," Galloway said in a phone interview.

It does not help that Haiti is beset by deep poverty and a history of disfunctional governance.

The critical role of construction quality is highlighted by comparing the Haiti quake with a similar one in Kobe, Japan in 1995.

"The Kobe earthquake was 6.9 on the Richter Scale, was almost as superficial -- less than 20 kilometers under the surface -- and very near the epicentre," said Lacassin. It was also the same kind of so-called slip-strike fault in which two plates rub past each other.

The death toll in Kobe was just over 5,000, considered shockingly high at the time because the city had been built to withstand intense ground shaking, but still only a fraction of the Haiti toll.

There is also an element of luck, depending on what time of day the pressure that has built up within Earth's surface layer, over decades or centuries, finally gives way.

"In Chile, a lot of car parks collapsed, but there was nobody in them because it was the middle of the night," noted Galloway.

Had the shaking started as people arrived at work or headed home, the tolls would be far higher, he said.

earlier related report
'God help us:' rescue worker at collapsed Chile building
Concepcion, Chile (AFP) March 1, 2010 - "We'll have to work with the precision of watchmakers. May God help us," fire chief Juan Carlos Subercaseaux said Monday as his team worked to free Chileans trapped in quake rubble.

Workers using specially-designed cameras and search dogs had located at least three survivors by afternoon, all trapped in the ruins of the massive 15-story Borde Rio building, which crumpled onto its back after Saturday's quake.

More than two days after the 8.8-magnitude quake, sounds of life were coming from apartment 602, where three, possibly four, people were believed to be alive, Diego Caruezo, head of fire department operations at the scene, told AFP.

A fifth survivor had been located close by in the building, which became a focal point for rescue efforts in the country's ravaged second city.

"We think that there are four people in one apartment and another in an apartment next door," Caruezo said.

Some 175 firemen worked to pierce the side of the building to get to some of the 35 people believed to be inside, though no one could say how many of the residents were still alive.

"Rescue team. Is there anyone there? If you can't speak, knock two times," a rescue worker said.

After a moment of absolute silence, a distant sound could be heard echoing through the ruins.

Firefighters marked up the length of the building, which now lay flush with the ground, painting numbers to indicate where each floor started -- 6, 7, 9.

"We can't explain why it fell over, rather than collapsing top to bottom like the Twin Towers," said Caruezo.

Subercaseaux told AFP the rescue operation was extremely delicate because drilling through walls to reach survivors could cause the entire structure to collapse and crush them.

Workers armed with machines capable of piercing the walls worked to create something like a tunnel between two floors to try to reach those trapped inside apartment 602.

Elsewhere, large triangles big enough for a person to escape through had been cut into the concrete.

Nearby, search dogs Berkan, Kuro and Queenie -- all veterans of the Haiti earthquake rescue effort in January -- stood ready to assist.

Crews had pulled eight bodies from the building and said a ninth had been located inside.

An emotional resident, Alex Tapia, told TV de Chile television station he had been inside when the building collapsed.

"I fell with the building and thank God I am here," he said. "It's like being born again."

Caretaker Ewin Jimenez said the building fell in a matter of seconds.

"First the pillars moved from side to side, then it collapsed and everything was destroyed," said Jimenez, who only survived because he jumped out of a window.

There were scenes of devastation throughout the city, with rows of collapsed buildings and cars crushed by chunks of concrete. There was no electricity and only patchy telephone communications.

President-elect Sebastian Pinera, in the region touring the worst-affected areas, described seeing sick people sleeping in the streets and hearing cries coming from collapsed buildings that rescue crews had not yet reached.

"The situation is worse than expected," he said.

Troops were deployed alongside police to keep the peace after looters began to comb through the ruins of supermarkets looking for basic foodstuffs and other items.

Deputy Interior Minister Patricio Rosende said the government had purchased all the food in the city's major supermarkets and planned to distribute it free of charge.

Food would also be brought in on a barge and two Chilean Air Force planes, he said.

But looting continued even after the imposition of a curfew, the first since the end of Augusto Pinochet's dictatorship in 1990, and Rosende said at least 160 people had been arrested for violating the measure.

Despite the arrests, he said most residents had observed the curfew.

"The public cooperated. It understood the need for a curfew. One has to understand the anguish that many people feel because on top of the constant aftershocks, there is the darkness, the uncertainty."

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