India earthquake: What makes the region so volatile?
A magnitude 6.9 Himalayan quake on the border between India and Nepal, highlights the extreme hazard the region faces as enormous patches of Earth's crust crash into each other.
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.Skip to next paragraph
In Pictures Nepal earthquake
Subscribe Today to the Monitor
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 PICTURES: Nepal earthquake
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.
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.