Tuesday, 15 March 2011

Japan: A Multi-Hazard Disaster

Our screens and newspapers have been filled with shocking images of the disaster in Japan over the past few days. In the age of 24 hour news, the world watched the disaster unfold as north-east Japan was struck by a major earthquake - 8000 times bigger than the one that struck Christchurch, New Zealand - followed by a tsunami causing widespread damage and destruction. The earthquake also triggered fires, landslides and now a possible nuclear disaster. In the coming weeks and months the full extent of the damage and loss of life will become clear.

The disaster in Japan demonstrates the complex nature of natural hazards, and the importance of forming a multi-hazard approach to preparing for and mitigating against natural hazards. The earthquake in Japan caused significant damage as buildings shook, roads cracked and structures collapsed. However it also triggered a number of other hazards. It had its epicenter under the sea, triggering the devastating tsunami that caused further damage and destruction. It caused slopes to become unstable, and landslides to occur. It caused gas leaks and subsequent explosions and fires. It has also potentially caused radioactive leaks, bringing a state of nuclear emergency.

Any of these hazards occurring on their own could cause significant damage - all of them occurring at one time is significantly worse than the sum of the damage that could have occurred if they'd been stand-alone disasters. For example, the damage to infrastructure from the earthquake would have increased people's vulnerability to the tsunami... making it more difficult to escape as roads were blocked etc. 

Landslide Blocked Roads:

The hazards will also have increased human vulnerability to other possible disasters, such as disease and aftershocks. Since Friday aftershocks have struck the region, and they are likely to continue for many more weeks to come. The biggest aftershock is normally around a magnitude less than the main earthquake, meaning a large earthquake of approximately M7.5 could hit the area in the near future. It is possible and likely that this will cause further damage. Some of the damage this will do as an aftershock (after a major earthquake) will be greater than the damage it would have done if had just occurred as the main event itself. Slopes that were brought to a level dangerously close to instability by the M8.9 earthquake could fail. Damage done to infrastructure such as dams that has not yet been repaired could be exacerbated and failure occur. A risk assessment done for a M7.5 earthquake following the damage and destruction of a M8.9 earthquake and tsunami will be different to a risk assessment from a M7.5 earthquake. 

Japan M8.9 Earthquake & Aftershocks: www2.demis.nl/quakes/

The complexity of the situation in Japan, and the interconnectedness of the natural hazards must be reflected in how we approach disaster risk reduction and risk assessments for urban areas. Treating hazards as discrete events is far from the reality, and can lead to increased vulnerability. This said, most of the existing work into multi-hazard risk assessments (with rare exceptions) still view hazards as discrete events and fail to take into account (i) a hazard triggering another hazard, (ii) synergistic hazards bringing a greater risk than the sum of the individual hazards, (iii) one hazard increasing the probability of other hazards occurring. There is a growing need for further work and research to be done in this important area in order to develop and improve disaster risk reduction programmes.