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The causes of the catastrophic earthquakes in Nepal are rooted in the same geological phenomenon that draws nearly a million tourists to the remote region every year: the crash of continental plates that produced the highest mountains in the world.
Hundreds of millions of years ago, what is now the Indian subcontinent broke off from an ancient supercontinent called Gondwanaland and began its inexorable drift northward, smashing into the Eurasian tectonic plate tens of millions of years ago and giving rise to the Himalayan mountain range.
That collision continues today, with the Indian plate sliding beneath the Eurasian plate at a rate of about 2 inches (40 to 50 millimeters) per year. "This is a very complex region where plates push against each other, and gravitational forces on the mountains push down," Lucy Flesch, a seismologist at Purdue University who has studied the region for almost two decades, said in an email.
The extreme strain occasionally causes ruptures in the region's crust — and the magnitude-7.8 earthquake that ripped through Nepal's Kathmandu Valley on April 25 was the unfortunate result. A 7.3-magnitude temblor followed on Tuesday.
It's unfortunate, but also unsurprising: An even more powerful 8.2 quake hit in 1934, killing more than 10,000 people in Nepal and India. The earthquakes that were experienced in India's Kangra Valley in 1905 and Pakistan's Kashmir region in 2005 left behind higher death tolls — 20,000 and more than 85,000, respectively. And the geological record reveals evidence of potentially stronger quakes going back to the year 1100.
"The region that experienced the earthquake Saturday is one of the most seismically hazardous regions on Earth," University of Michigan geophysicist Marin Clark said in an email. "So from a scientific perspective, this earthquake was quite expected."
Susan Hough, a seismologist at the U.S. Geological Survey who traveled to Nepal several times for research before last month's temblor, said the Nepalese are well aware of the risks.
"You get a cultural fatalism," she told NBC News. "You get a lot of people who feel that the situation is so far out of their control that they can't do anything about it, so they leave it up to God."
The shortcomings of Nepal's earthquake preparedness have been well-documented for decades, and most recently during a conference that took place in Kathmandu this month. The warnings have been borne out in grim reports: Older buildings were flattened by the seismic shock, due to shoddy or outdated construction techniques.
Hough saw some rays of hope in videos from camera-equipped drones surveying the city. "Look at the background, and all the buildings that are still standing," she said. "That surprises me. So maybe there's going to be a success story emerging from Kathmandu itself. I think the scary story is the story we're not yet hearing from the outlying villages."
Roger Bilham, a geologist at the University of Colorado at Boulder, echoed Hough's comments about the damage.
"I am not at all surprised at what has been damaged, but am pleasantly surprised that some of the buildings have survived," he told NBC News. "We had estimated that 40,000 people would be killed by a magnitude-8 earthquake ... so the death toll here, while it's depressing, could have been worse."
Nepal's preparedness efforts have faced special challenges — due to the landlocked country's remoteness as well as its poverty and population growth. "Nepal is about a third the size of California, geographically, with 30 percent more people," Hough said. After agriculture, Himalayan tourism is Nepal's biggest industry — but that industry's future is now in question, due to the earthquake as well as last year's widely publicized Everest avalanche.
With all of Nepal's social and economic challenges, there's not much money left for seismic studies and preparedness measures — which have "tended to be run on a shoestring," Hough said.
That situation isn't unique to Nepal.
Bigger problems with preparedness
"The world community is just not good about disasters that we know are going to happen," Hough said. "The resources materialize after you have a disaster. ... It's the preparedness that you just can't get funded."
She acknowledged that seismometers don't save lives, but said that better seismic monitoring networks could be the cornerstone of better hazard assessments. Having a better sense of seismic activity could help scientists, aid agencies and government officials gain support for more stringent building codes, upgraded emergency response and communication systems, and higher public awareness.
Hough and her colleagues have been working to improve seismic networks, not only in Nepal and the Himalayas, but throughout southern Asia. After all, Kathmandu isn't the only city that's at risk because of those crashing continental plates.
"In Myanmar, Yangon could potentially have a big earthquake," Hough said. "People worry about Bangladesh and northern India. New Delhi is close enough to the Himalayan range that an earthquake could be much worse there. There's Pakistan, Iran, Turkey ... There's no shortage of earthquake zones."
NBC News correspondent Hallie Jackson contributed to this report from Los Angeles.