How to predict an earthquake (clue, you can't)

The world's tectonic plates

As aid workers deal with the crisis in Nepal, many are asking whether the devastating earthquake could have been predicted.

In 2007, Kathmandu, Nepal's capital, was named the most earthquake vulnerable city in the world.

The science of studying earthquakes is called seismology. So how does it work?

"It is virtually impossible to provide any meaningful prediction of earthquakes in terms of location, time and size," says Tarje Nissen-Meyer.

He is an associate professor of geophysics at Oxford University and told Newsbeat that seismologists tend to focus on places that have been hit before, and whether they'll be affected again.

So here are the main places experts are currently watching.

India and Nepal

The world is divided up by tectonic plates and countries that sit along these lines - where the earth's crust is constantly shifting - are the most likely to experience a quake.

Nepal is situated along the Himalayas, where there is a lot of seismic activity, and where the whole length of the top of India could be affected.

Roger Musson, from the British Geological Survey, told Newsbeat that India has "tectonics the same as Nepal" and "an earthquake larger than Saturday's could occur further west."

Large cities like Kathmandu are particularly at risk because they are built on thick layers of soft rock which increases the amount of ground shaking caused by an earthquake.

Debris after earthquake in Duzce near Istanbul
Image caption Locals search debris after an earthquake 200 km east of Istanbul in November 1999

Turkey

Turkey is another nation affected by deadly quakes in recent years.

The North Anatolian fault runs from east to west across most of Turkey. An area to the east of Istanbul behaves a bit like a zip, where two plates are sliding against each other horizontally, and parts of the plates are unzipping at different times.

Iran

Tehran, the capital of Iran, is built on an active fault line, the Arabian plate.

"The city itself is sat right on top of part of the fault which appears to have been active in the recent past and may rupture in a future earthquake," says Dr John Elliot, science researcher at the University of Oxford.

In 2003 a magnitude 6.6 quake hit the city of Bam, causing more than 26,000 deaths and injuring as many.

Tehran
Image caption "Tehran is sat in the shadow of mountains that have been built by successive rupture of faults in large earthquakes" John Elliot

China

China is at risk because of the plates colliding between India and Eurasia.

In 2008 the Wenchuan quake caused nearly 90,000 fatalities and left nearly five million people homeless.

"Earthquakes here tend to be rather shallow so result in strong shaking intensity.

"Coupled with this, buildings are not very resistant to earthquake shaking, particularly in the remotest areas which can be hard to access to provide aid in the aftermath of an earthquake," says Stephen Hicks, a seismologist based at the University of Liverpool.

Japan

The aftermath of the Japan earthquake in 2011
Image caption The aftermath of the Japan earthquake in 2011

A great earthquake offshore west of Tokyo has been expected for years but the Japanese are well-prepared.

The 2011 magnitude 9 Tohoku earthquake was deadly because of the tsunami it triggered.

"One area of particular concern is beneath Tokyo, a city of 13 million people. Lurking beneath Tokyo, several tectonic plates meet at shallow depths, so there are a number of sources of seismic hazard in the region," says Hicks.

US and Canada

San Francisco
Image caption Steven Hicks says authorities are taking no chances in America there is a lots of research into seismic activity

Northern California, Oregon, Washington and an area of Canada lie close to a major fault line separating two colliding plates: the Juan de Fuca plate and North America plate.

Large cities along this line are vulnerable, including Los Angeles, San Francisco, Seattle and Vancouver.

"This fault has been eerily quiet for quite some time," says Hicks, but "a great deal of research is being carried out to assess the future hazard in this area to avoid a repeat of the effects caused by the 2011 Japan tsunami."

Anywhere else?

Experts warn we can be surprised by hidden fault lines. For example, Christchurch in New Zealand where an earthquake struck unexpectedly in 2011.

The fault was under the city but no-one knew it was there.

"Earthquakes continue to surprise scientists and we cannot yet state where and when an earthquake is definitely going to occur," concedes Stephen Hicks.

Tarje Nissen-Meyer says: "A lot of our current work focuses on simulating earthquake waves on supercomputers to better understand intense ground shaking caused by local amplification. Such simulations can be useful to improve building reinforcement and safety measures for critical infrastructures."

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