Earthquakes: What's the difference between Nepal and Oklahoma?

Nepal's massive earthquake has scientists discussing about what other big quakes may be in store in the future.

MPR News' Kerri Miller also looked at the recent phenomena of man-made earthquakes in places like Oklahoma, where fracking appears to be causing nearly daily seismic events.

Your earthquake questions, answered

Why did the Nepal earthquake happen?

"The Himalayan mountains are these huge mountains because India has been crashing into Eurasia," Andrew Michael said. "Since they are both continents, neither one of them wants to go underneath the other and instead they create this collision zone and build these very tall mountains. There's no way to build mountains like that without having earthquakes as part of the process."

Scientists know India is moving a couple inches northward each year and these major earthquakes release tension in the location along the fault where the plates slipped. But Michael said it's more like one strand in a rope snapping: The tension moves to other strands or other parts of the fault. This movement of tension causes other areas of increased stress and the aftershocks they're seeing in Nepal.

How are earthquakes caused during fracking process different from earthquakes in places like Nepal?

The fracking process, which produces oil and gas, also produces a lot of salt water waste, said Todd Halihan. That water needs to be disposed of, so fracking operations are using injection wells to send that water underground. That injection causes the earthquakes Oklahoma is experiencing.

"Most places on the earth are a bit stressed out," he said. "The rocks are being pushed around by tectonic movements and things so there's already stresses there and energy built up. What happens is that fluid when it's being injected can act as a lubricant."

Halihan compared it to an air hockey table.

"If you've got an air hockey puck and you've got the air off, it's very hard to move it, but you turn that air on and release that pressure, it's quite easy to move that puck around," he said. "Particular faults around Oklahoma where they're at the right angles relative to the forces pushing onto that state, when you get that water into the right spot it's relieving that tension on that fault and allowing it to slip a bit."

Why do we have to send that water back into the earth?

Halihan said keeping that salty water on the surface is the easiest way to contaminate fresh water. The water waste from fracking is also much saltier than typical sea water on earth. The salt content in sea water is 35,000ppm compared to 150,000ppm in fracking waste. Trying to desalinate that water would produce very little fresh water and cause more challenges to dispose of the brine.

Why don't we know more about where earthquakes can happen or have the ability to predict them?

"The hard part is just seeing inside the earth," Michael said. "We don't actually know where all these important faults are because, especially in areas like Oklahoma, they're buried underneath sediments that we can't see through and it's very difficult to do that imaging. The best way to find these faults is actually when they produce earthquakes."

Michael said better seismic monitoring, which requires more resources, could help scientists detect smaller earthquakes that could provide insight into the fault lines.

Could we use water injection to relieve energy and control earthquakes?

Maybe, but it's risky, Halihan said. The process requires releasing major tension by controlling the sliding of plates in highly stressed areas, but then a multiplying number of smaller earthquakes can end up being just as disastrous depending on where they hit. Scientists also risk losing control of the plate slides and it could cause a bigger earthquake somewhere else they weren't expecting.