On the afternoon of March 11th, 2011, Japan lurched eastward as the Pacific crust plates jolted beneath it. The sea floor shifted forward 60m in places. The offshore quake caused a massive tsunami, which inflicted more than 15,000 fatalities and crippled the Fukushima nuclear power plant.
On Monday afternoon next, Dr Yoshiyuki Kaneda from Japan will deliver a lecture in Dublin on lessons learned from this catastrophe, and will also warn of a threat hanging over Tokyo.
There is concern the 2011 event has increased the chances of a massive earthquake on a separate fault close to Tokyo, a mega-city of 35 million. Worryingly, there has been an uptick in tremors around the city, leading Japanese scientists to warn a quake is imminent. The Japanese government puts the probability of a large Tokyo quake (magnitude 8 or 9) at 60-70 per cent within 30 years. The city was ruined twice by earthquakes, in 1855 and 1923.
Unfortunately scientists cannot predict when an earthquake will happen; they are better at estimating its likely size.
Kaneda, of the Japanese Agency for Marine-Earth Science and Technology, says the power of the 2011 quake surprised experts. “We misunderstood. We estimated the seismogenic zone off east Japan was composed of small and medium-sized areas, but the 2011 great east Japan earthquake showed this zone is of a huge scale too.”
The massive rupture extended for about 400km, generating the fourth-largest earthquake ever recorded.
Japan had built defences for the strongest earthquake predicted, a magnitude 8; when the magnitude 9 pushed a huge tsunami landward it vaulted 15ft flood defences. Waves reached more than 30ft in places. Kaneda attributes the massive damage to incorrect predictions, too much confidence being placed in breakwaters and not enough evacuation awareness.
“We learned that sometimes natural disasters occur over our assumptions, and that is why real-time monitoring and simulation research is important,” Kaneda will tell his audience.
An offshore network of 20 sensor stations gave 15 minutes’ extra warning of the tsunami, and Kaneda’s group is now working on a second network consisting of 31 observatories. Accelerometers, pressure gauges, hydrophones and seismometers will all listen for crustal movements offshore. Warnings improve evacuations, thereby saving lives.
Shockwaves from the 2011 quake arrived in Ireland just 13 minutes after the quake. Tom Blake of the Dublin Institute for Advanced Studies (DIAS), who leads the Irish National Seismic Network, recalls sitting at his desk and seeing the ripples recorded at European stations. "Suddenly the line went flat, and that signalled the onset of a very major event. It was a strange moment. You were able to see the vibrations pass beneath our seismic stations."
The vibrations were so strong, the water levels in wells around Ireland fluctuated.
Ireland is not immune to tsunamis. “We have strong evidence of tsunamis in the geological past. But more recently, in 1755 and 1761, we had two large tsunamis hit the south coast of Ireland,” Blake says, the former causing 15ft waves.
“There are geological reasons why there could be [tsunamis],” agrees Dr Brian McConnell of the Geological Survey of Ireland. Coastal development makes us more vulnerable today.
Ireland has five national seismometer stations. Blake says they regularly detect earthquakes off the Spanish and Portuguese coast, a complex area of faults. These are normally deep quakes. "For a tsunami, an earthquake would have to be [at least] magnitude 6 and shallow," Blake explains. Earthquakes around the Azores or Caribbean could send one our way. Some suggest an eruption on Las Palmas in the Canaries could do the same.
“Our models suggest a tsunami wave would not exceed the largest storm surges,” says McConnell, “but it would be a sudden event. People don’t go down to the beach on stormy days, but a tsunami could happen out of the blue. You would have to warn people.”
It would take a tsunami more than three hours to travel from the Gibraltar-Azores fracture to Ireland, but we do not have a tsunami warning system. Getting policy makers interested in such a system is difficult because it has never happened in our lifetime, say Irish experts, but it is being considered by the EU.
The 2011 quake is expected to recur every 300-400 years off Japan. "It may have a 400-year average if you look at 1,000 earthquakes, but the next one could be in 2,000 years or it could be tomorrow," warns seismologist Dr Mark Simons of the California Institute of Technology.
Blake says Europe is looking at tsunami warning systems, and there may be openings for Irish technology companies.
A lecture by world expert on earthquakes and tsunamis Dr Yoshiyuki Kaneda will be held at 2.30pm on Monday, February 3, at DIAS (10 Burlington Road, Dublin 4). Reserve a place at cultural@ir.mofa.go.jp
KEEPING TABS: PUPILS MONITOR EARTHQUAKES
Students at St Mary's College in Rathmines could be the first in Ireland to detect signs of the next mega-earthquake. The school is equipped with a seismometer, which monitors quakes as they happen. It is one of 60 primary and secondary schools to have received the device as part of the Seismology in Schools pilot project, which is run by the Dublin Institute for Advanced Studies. The school seismometers could even detect secret nuclear tests, such as those in North Korea in February 2013.
John Nisbet, a science teacher at St Mary’s, says the pupils find it difficult to realise how much tremors can spread. “With the seismometer in school, they can see earthquakes over the other side of the globe and the direct impact on the device. They sit there and see the needle on the computer screen moving as the earthquake happens.”
Gerry Aylward, a physics teacher at Blackrock College, which also has a seismometer, says “the students are amazed that this weird-looking contraption in the corner can actually pick up signals from across the world. It makes science real for them. It just looks like a pendulum in a perspex case. It sits on the floor connected to a computer.”
Blackrock students have detected tremors off Australia, off Cape Verde and other locations. There is always some activity, signalled by onscreen squiggly lines, which spike rapidly during an earthquake.
“The big earthquake in Japan [in 2011] had a dramatic impact on the trace. You would know there was something serious going on,” says Aylward. More at dias.ie/sis.
