Japan earthquake - what the experts are saying

11 March 2011

Some of NERC's researchers offer expert opinions about the earthquake.

Dr Roger Musson, BGS Head of Seismic Hazard says:

"This is the sixth largest earthquake that's ever been recorded since seismographic records began in 1900. It's certainly the largest earthquake to have affected Japan in the last century and considerably larger than anything else in living memory in Japan.

"The largest previously was the 1923 Canto earthquake, the one that caused so much damage in Tokyo, that was only 7·9. That's 30 times less powerful than this one."

Professor Dave Tappin, Marine geologist, expert in tsunamis, says:

"You need an earthquake of larger than 7 to produce a dangerous tsunami, this one was 8·9. This tsunami will travel around the world. The Indian Ocean earthquake of 2004 which was 9·3 sent a tsunami around the world 3 times."

In an interview with the BBC, Dr John Elliott, an earthquake expert at Oxford University who is funded by NERC, said that Japan has so far coped well with such a huge quake. "They have had many earthquakes in their history and they have learned from this and they build appropriately for it," he said. "The tsunami is much harder to deal with. They have hundreds of kilometres of coastline and low-lying areas and it is hard to mitigate against the direct effect of such large event."

In a separate BBC interview, Simon Boxall from the National Oceanography Centre in Southampton explained how a quake triggers a tsunami:

"An earthquake with the epicentre on the seabed rather than inland is a bit like throwing a huge boulder into the water." Dr Boxall said that as a result the waves moving away from the epicentre "move incredibly fast, in fact in the deep water they move at 800kmh. But as they get to shallower water, the front of the waves slows down, the back of the waves keep going at full speed. So what starts off as a ripple that may only be 20 or 30cm high ends up with a wave that piles up to an excessive 10 metres. That is what happened here. And of course this part of north-east Japan is very low-lying, so it's become swamped incredibly quickly."

Dr Richard England from the University of Leicester works on SEIS-UK, part of NERC's Geophysical Equipment Facility. He says:

"In Japan the immediate danger will now be from continuing aftershocks. There was a M 7·1 event this morning which would normally be considered a strong earthquake. These 'smaller' events will still have the potential to generate small tsunami and further shake buildings and infrastructure already damaged, further delaying rescue and relief efforts."

Are these events becoming more common? Dr England says they are not. "The timing of earthquakes is not predictable, although seismologists are getting better at being able to determine which areas are most at risk. The December 2004 event raised awareness of the possibility of major earthquakes and the devastating effects they can have on communities. As a result they are much better reported so everyone takes more notice when they occur."

Further information

NERC Press Office
Natural Environment Research Council
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Press release: 09/11

Japan earthquake - what the experts are saying

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