The awesome power unleashed upon the east coast of Japan last month is a stark reminder of the challenge engineers face trying to tame ‘mother nature’. Even the most sophisticated warning systems and robust construction could not save the lives of the tens of thousands that perished in the earthquake and resulting tsunami on 11 and 12 March.
Earthquakes are a way of life in Japan. Major earthquakes occur every couple of weeks and minor tremors can be detected daily. But as Professor Osamu Kiyomiya of Waseda University, Tokyo writes on page 12, the 9.0 magnitude earthquake went beyond seismologists’ forecasts and past anything engineers had prepared for.
The statistics rolling out of universities and research laboratories observing this quake all over the world have made clear the power that mega earthquakes unleash and the challenge engineers have to overcome. The 11 March quake is the fourth largest recorded since 1900 and was caused when the Pacific tectonic plate dived under the North American plate, shifting eastern Japan towards North America by about 4m. The quake also shifted the earth’s axis by some 150mm, shortened the day by 1.6 microseconds, and sank Japan downward by about 1m. As Japan’s eastern coastline sunk, the tsunami’s waves rolled in. The 10m waves breached sea walls up and down the coastline.
The damage to underground infrastructure is not yet known. But it will be there. Earthquakes occur many kilometres below the surface but it is in the last tens of metres that they are at their most destructive. As the shock waves pass from the hard rock into weaker ground they are amplified. Cut and cover tunnels and utility infrastructure near the surface will be the worst affected. In his comment article Prof Kiyomiya details the damage caused to underground infrastructure from previous earthquakes of a lower magnitude. This list is an indicator or what might be waiting for engineers when they begin to assess the damage.
Despite the obvious devastation and the lack of preparedness for an earthquake of this agnitude, Japan is still a success story. The early warning systems gave people a few extra seconds to react before the deadly shock waves shook the county. Many of the buildings behaved exactly as they should, swaying from side to side. It is standard in Japan to construct buildings for horizontal loading as well as vertical loading. The tsunami warning system gave coastal towns and cities nearly 20 minutes to evacuate. There is no telling how great the death toll may have been if those measures had not been in place.
The recovery will be slow. As the wreckage clears, the task of rebuilding will begin. Japan is a wealthy country and will rebuild its towns and cities to better withstand earthquakes and tsunamis. They are less reliant on foreign assistance than some of the other countries lying in seismically active regions. The charity RedR usually sends response teams to regions hit by natural disasters to help with the immediate rescue, short-term shelters and then the eventual rebuild. RedR has not had to do so for Japan. But the next disaster may not hit a developed country like Japan, and RedR may be called upon, and so T&TI has become a supporter of RedR and has pledged 10 per cent of future revenue from every individual subscription to the charity.
Jon Young
