Nepal earthquake: Shallow quakes pack more punch

The U.S. Geological Survey put the magnitude of Saturday's quake in Nepalat 7.8. It said the quake hit at 11:56 a.m. local time atLamjung, about 80 kilometres northwest ofKathmandu. Its depth was only 15kilometres, the largest shallow quake since the 8.2 temblor off the coast of Chile on April 1, 2014.

Quakes that are closer to the surface carry more destructive power, and witnesses said the trembling and swaying of the earth went on for several minutes.

• Nepal 7.8earthquake hits populated Kathmandu Valley
• Earthquake triggers Everest avalanche, killing climbers

A magnitude 7 quake is capable of widespread and heavy damage while an 8 magnitude quake can cause tremendous damage. This means Saturday's quake with the same magnitude as the one that hit San Francisco in 1906 was about 16 times more powerful than the 7.0 quake that devastated Haiti in 2010.

"The shallowness of the source made the ground-shaking at the surface worse than it would have been for a deeper earthquake," said David A.Rothery, professor of planetarygeosciencesat the Open University in Milton Keynes, north of London.

All the houses around me have tumbled down.- WitnessJennyAdhikari

A major factor in the damage was that the buildings were not built to be quake-proof. An earthquake this size in Tokyo or Los Angeles, which have building codes for quake resistance, would not be nearly as devastating.

The power of the tremors brought down several buildings in the center of the capital, the ancient OldKathmandu, including centuries-old temples and towers.

Among them was the nine-storeyDharaharaTower, one ofKathmandu'slandmarks built by Nepal's royal rulers as a watchtower in the1800sand a UNESCO-recognized historical monument. It was reduced to rubble and there were reports of people trapped underneath.

Hundreds of people buy tickets on weekends to go up to the viewing platform on the eighth story, but it was not clear how many were up there when the tower collapsed. Video footage showed people digging through the rubble of the tower, looking for survivors.

Buildings poorly constructed

TheKathmanduValley is densely populated with nearly 2.5 million people, and the quality of buildings is often poor.

InKathmandu, dozens of people gathered in the parking lot ofNorvicInternational Hospital, where thin mattresses were spread on the ground for patients rushed outside, some wearing hospital pajamas. A woman with a bandage on her head sat in a set of chairs pulled from the hospital waiting room.

Doctors and nurses hooked up some patients to intravenous drips in the parking lot, or were giving people oxygen.

A Swedish woman, JennyAdhikari, who lives in Nepal, told the Swedish newspaperAftonbladetthat she was riding a bus in the town ofMelamchiwhen the earth began to move.

"A huge stone crashed only about 20 metres from the bus," she was quoted as saying. "All the houses around me have tumbled down. I think there are lot of people who have died," she told the newspaper by telephone.Melamchiis about 45 kilometres northeast ofKathmandu.

• 4 things to know about earthquakes
• Richter 'magnitude' scale explained

Nepal suffered its worst recorded earthquake in 1934, which measured 8.0 and all but destroyed the cities ofKathmandu,BhaktapurandPatan.

The sustained quake also was felt in India's capital of New Delhi and several other Indian cities.

India's Prime Minister Narendra Modi called a meeting of top government officials to review the damage and disaster preparedness in parts of India that felt strong tremors. The Indian states of Uttar Pradesh, Bihar and Sikkim, which share a border with Nepal, have reported building damage. There have also been reports of damage in the northeastern state of Assam.

Pakistan Prime Minister Nawaz Sharif offered "all possible help" that Nepal may need.