KATHMANDU - More than 25 million years ago, India, once a separate island on a quickly sliding piece of the earth's crust, crashed into Asia.
The two land masses are still colliding today, pushed together at a speed of 3.8cm to 5cm a year.
The forces have pushed up the highest mountains in the world in the Himalayas, and set off devastating earthquakes.
Experts have warned of the danger to Kathmandu for decades.
GeoHazards International, a non-profit organisation in California that tries to help poorer, vulnerable regions like Nepal prepare for disasters, noted that major earthquakes have struck that region every 75 years or so.
In 1934 - 81 years ago - more than 10,000 people died in a magnitude-8.1 earthquake in eastern Nepal, about 10km south of Mount Everest. A smaller quake in 1988 killed more than 1,000 people.
Mr Brian Tucker, president and founder of GeoHazards, said that in the 1990s his organisation predicted that if the 1934 quake were to happen again, 40,000 people would die because of migration to the city where tall, flimsily built buildings would collapse.
In an update just this month, GeoHazards wrote: "With an annual population growth rate of 6.5 per cent and one of the highest urban densities in the world, the 1.5 million people living in the Kathmandu valley were clearly facing a serious and growing earthquake risk."
The organisation has helped to set up a local non-profit organisation to continue preparations, including reinforcing schools and hospitals.
Last Saturday's quake occurred to the north-west of Kathmandu at a relatively shallow depth, about 145km. It caused greater shaking at the surface but, at magnitude 7.8, released much less energy than the 1934 quake.
University of Colorado professor of geological sciences Roger Bilham, who has studied the history of earthquakes in that region, said that the shaking lasted one to two minutes, and the fault slipped about 3m along the rupture zone, which stretched 120km along the fault, passing under Kathmandu.
Kathmandu and the surrounding valley sit on an ancient dried-up lake bed, which contributed to the devastation.
"Very, very soft soil, and the soft soil amplifies seismic motion," Mr Tucker said.
Steep slopes in the area are also prone to avalanches like the one that the quake triggered on Mount Everest last Saturday.
Kathmandu is not the only place where a deadly earthquake has been expected.
Mr Tucker said that the Iranian capital of Teheran, Haiti, Peru's capital Lima, as well as Padang in Indonesia, were similarly vulnerable. Building standards and disaster preparations in those places are seen as inadequate.
However, there has not been complacency everywhere.
An earthquake in 1999 killed more than 17,000 people, mostly in the Turkish city of Izmit, to the east of Istanbul.
The expectation is that the epicentre of the next big earthquake will be in or around Istanbul.
"Istanbul is the place that has been most aggressive in enforcing building codes," Mr Tucker said. "I think Istanbul has been doing a good job."
NEW YORK TIMES
