Why the major earthquakes in Nepal are unlikely to stop any time soon

There have been many more subsequent earthquakes following the magnitude-7.8 one that killed more than 8,000 people on April 25, and the region could continue to see more.
There have been many more subsequent earthquakes following the magnitude-7.8 one that killed more than 8,000 people on April 25, and the region could continue to see more. AP Photo/Niranjan Shrestha, File

TORONTO – With two earthquakes killing more than 8,000 people in Nepal and injuring thousands of others, many are wondering when the shaking will stop. The answer? Not any time soon.

READ MORE: 2nd deadly earthquake spreads fear, misery in Nepal; killing at least 37

The magnitude-7.8 earthquake that hit the country on April 25 lifted an area around the city of Kathmandu — about 120 km by 50 km —  by about one metre.

Some data suggest that the Himalayan range, including Mount Everest, may have dropped as a result. However, the changes are likely temporary, as the fault and area around it settle.

WATCH: Earthquake interrupts Nepalese parliament, politicians run for safety

But the energy that has been stored from that movement of tectonic plates is a worry for seismologists and geophysicists around the world: most believe that the energy stored hasn’t yet been released. And that is bad news for people living in the region.

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A history of movement

Earth used to be one supercontinent, called Pangaea. It began to break up and eventually drifted, forming the continents we know today. But those plates are still moving, triggering earthquakes around the world.

In the Nepal region, there is the interaction of two plates: the India Plate and the Eurasia Plate. The India Plate is moving rapidly — about 20 mm a year by some estimates. While that may not sound like much, it’s faster than the movement of the plates responsible for the San Andreas Fault in California, which is moving at a just 2 mm a year (it’s important to remember that these are averages over a long period of time).

Earth’s tectonic plates. USGS

That India-Eurasia plate zone is considered quite an active region. In 1934, Nepal experienced a magnitude-8 earthquake that killed more than 10,000 people. The earthquakes that rock India and Pakistan are also due to movement in the plates.

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Potential for disaster

Preliminary data suggests that the magnitude-7.8 earthquake that rocked the region on April 25 created a slip of 4.5 metres along a 150 km fault. But all that stored energy from the plates’ movement means that the earthquakes are going to continue. And they could be significant.

READ MORE: IN PHOTOS – Powerful images from the Nepal earthquake

“As [the India Plate] is moving 4.5 metres, it’s not the entire fault surface that’s moving…the surface hasn’t moved yet,” said Laurent Godin, a structural geologist and professor at Queen’s University. “There hasn’t been a fault rupture there yet. Meaning the fault hasn’t released all its stress.”

Typically, following a major earthquake, the aftershocks will decrease in frequency and magnitude over time. However, a large one can cause a previously stable area along the fault to become unstable, which is likely what triggered Tuesday’s magnitude-7.3 earthquake.

And Godin said that the earthquake is moving the slip eastward. The swarms of earthquakes following the April 25 event have mainly occurred to the east of the original event.

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This map illustrates the swarm of earthquakes that have continued to move eastward following the magnitude-7.8 earthquake that shook the region on April 25, 2015. USGS

However, that doesn’t mean the earthquakes will only move eastward. It could also move westward.

“The worst case scenario, is that it could go south and breach the surface south of Kathmandu. And if it does that, keep in mind that the fault surface goes right under Kathmandu.”

And things could get a lot worse: monsoon season is around the corner. Scientists are uncertain as to what that added water will do to an already unstable fault. And what that could even do to the people who remain homeless.

If an earthquake of that magnitude hit the region, it could be catastrophic. Between an already fragile infrastructure system and thousands of emergency workers on the scene, it could create a disaster the region hasn’t seen in many years.

WATCH: Earthquakes continue to rock Nepal

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Don Blakeman, a geophysicist with the U.S. Geological Survey in the United States said that the recurring earthquakes we’re seeing — in particular the swarms of smaller ones — isn’t unusual.

“It’s typical, actually,” he said. And he agreed: more is likely to come.

And though it may seem like we’re seeing more earthquakes of late, this too is typical: Earth can go through periods of what seem like heightened activity followed by periods of relative quiet.

As with most things in nature there is no knowing for certain what will happen. There could be many magnitude-6 or lower earthquakes across the region. Or there could be a major one.

“There’s certainly room there for another 7. Will it go eight? We know the fault system is capable of going to an 8.4 because it has in the past.”

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