A magnitude 6.9 earthquake centered near Sikkim, India, along Nepal's eastern border, highlights the significant quake hazard the region faces as enormous patches of Earth's crust collide and dive under one another.
So far the Himalayan quake, which struck at 6:10 p.m. local time Sunday, has reportedly killed 53 and destroyed more than 100,000 homes.
Heavy rain is hampering relief efforts in a part of the world where building codes – if they exist for seismic hazards at all – are often poorly enforced.
In 1934, a magnitude 8.2 quake struck the region. The death toll from that event has been estimated at 30,000 people. The eastern end of the fault segment that ruptured at that time ended where Sunday's quake occurred, Dr. Avouac says.
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For the past 15 years, networks of GPS receivers places in key spots along the Himalayan range have been measuring the build-up of strain – strain that smaller quakes, including Sunday's, have failed to relieve.
"We know that such earthquakes are overdue," Avouac says, referring to the 1934 event. "We have a lot of energy that needs to be released at some point."
That energy comes from the actions of one of the most dynamic plate boundaries on the planet – where two enormous, migrating patches of the planet's surface are vying to occupy the same spot.
The story, as best as scientists can tell, starts about 150 million years ago. A chunk of Antarctica split from the continent to begin its transformation into India and Madagascar. By 90 million years ago, India and Madagascar had split, with India headed north into the Tethys Sea.
By 35 million years ago, India was well into its slow-motion collision with what would become Eurasia.
India's transoceanic cruise was slower than a snail's pace by Formula One standards. But in the world of plate tectonics, India moved a blistering 30 feet per century. (By contrast, California's San Andreas fault, the border between the North American and Pacific plates creeps along at an average pace of around 16 feet per century.)
Then bam! India met Eurasia.
Once the Big Crunch began, India slowed to roughly half of its pre-collision speed.
Often, head-on collisions between plates take place along ocean trenches as denser ocean crust slides beneath more-buoyant continental crust, or one slab of oceanic crust slides under another. This action, known as subduction, triggers the most powerful earthquakes on the planet. And it builds mountains – most notably, volcanoes.
In India's case, however, sub-continent met continent in a crust-buckling collision that continues to build the Himalayan Mountains to this day. The collision involves the upper portion of India's crusts. Meanwhile, India's deeper, denser crust is thought to be sliding beneath the Tibetan Plateau, giving that feature its high elevation.
In effect, India and Eurasia meet along a subduction zone without volcanoes.
Responding proactively to the region's seismic risk is a challenge, notes Brian Tucker, a geophysicist who heads GeoHazards International, a non-governmental organization aimed at helping communities increase their resilience to seismic hazards.
Even top officials in Nepal haven't been fully aware of the repeated risk their country faces, he says.
Dr. Tucker recalls meeting with one cabinet minister who, when discussing the need for better building codes, replied, "I really don't understand why you're here, because we already had our earthquake, in 1934," Tucker recalls.
"Outside his window you could see the Himalayas," Tucker conitinues. "I told him that as long as you see those mountains, you are in earthquake country."
Although designing for earthquake resistance can add between 5 percent and 10 percent to the cost of a building, even people in low-income countries will opt for it, he says.
And schools are a good place to start if the results from 12-year-old Nepalese project are any indication.
GeoHazard International commissioned a survey of villages to see which buildings residents were willing to pay extra to see reinforced. The winner: Schools.
So the organization teamed up with locals to work on the schools. So far, the buildings haven't undergone the ultimate test, Tucker says. The hope is, however, that when a quake does occur, residents will see the benefits of building for earthquake resistance and begin to follow suit with other buildings, including their homes.
But cities are a tougher nut to crack.
Within the past 10 months, a group of Tucker's colleagues when back to Kathmandu, the Nepalese capital, to gauge the city's progress.
"They were really disheartened," he says. "Population is booming and they being continually put in these very vulnerable, treacherous buildings" that continue to rise, he says.
One tack his group is considering: Putting a focus on new hotels, which cater to tourists and diplomats. The approach might seem odd given the economic vulnerability much of the Nepalese population, he acknowledges.
But the incentives are there, he continues: Nepal relies heavily on tourism for income. And these hotels often serve as residences and offices for diplomats and international organizations, as they did in Haiti before a devastating quake there in 2010 reduced those hotels to rubble.
These buildings would hold the potential to serve as examples for quake-resistant construction techniques and, if the need arises, as examples of the benefits those techniques yield when a quake strikes, he suggests.