A massive block of the Earth’s crust, roughly 75 miles long and 37 miles wide, lurched 10 feet to the south Saturday over the course of 30 seconds. Riding atop this block of the planet was the capital of Nepal – Kathmandu – and millions of Nepalese.

That’s the description of Saturday’s earthquake from University of Colorado geologist Roger Bilham, a world-renowned expert on Himalayan earthquakes. The 7.8-magnitude earthquake that flattened historic buildings in Kathmandu and has taken more than a thousand lives is the latest release of built-up strain from the collision of two of the Earth’s tectonic plates.

The India plate is inexorably sliding, in a halting, ground-shaking fashion, northward, beneath the much larger Eurasia plate. The process has created the lofty Tibetan plateau and pushed up mountains that reach nearly 30,000 feet above sea level. The Himalaya front can produce earthquakes that are much more powerful than the one on Saturday – such as the 8.2-magnitude earthquake that hit Nepal in 1934.

But this one was relatively shallow, which intensifies the surface shaking, and its epicenter was closer to Kathmandu than the 1934 temblor.

“The earthquake ruptured under the city, very close to the city, so this is as bad as our worst-case scenario, probably,” Bilham said.

Experts predicted the death toll will mount steadily into the many tens of thousands.

“I expect that there’s devastation scattered all around Nepal that we’re not even glimpsing at this point,” said Susan Hough, a geologist with the U.S. Geological Survey who has made multiple trips to Nepal.

The news hit Hough and colleagues hard. This earthquake had been long anticipated.

For years, experts on seismic hazard have kept a list of cities most vulnerable to a catastrophic earthquake. Kathmandu has always been high on the list.

Geology, urbanization, architecture and building codes have conspired to increase the vulnerability of the Nepalese, experts say, and the only major unknown has been the timing of the disaster.

“We knew it was going to happen. We saw it in ’34,” Hough said. “The earthquakes we expect to happen do happen.”

Scientists, engineers and government officials have worked in recent years on retrofitting schools and hospitals to make them sturdier in a temblor. But at the same time, civil unrest has pushed more people into urban areas, where they inhabit newly constructed, unreinforced-masonry buildings that in many cases are not designed to withstand a quake.