This article was published in the Aberystwyth University News Letter Issue 5, 2011. For full illustrated article please click here and see p10 in the PDF.
The magnitude 9.0 Tohoku earthquake on March 11, 2011 is one of the most documented disasters in history with video footage, photographs, and TV documentaries providing rapid insights into the devastation following the quake. Like millions around the globe, I viewed this footage with horror and a sense of disbelief; the destruction and trauma witnessed are difficult to rationalise. Yet, the early warning system in place saved the lives of at least 50,000 to 100,000 people demonstrating that the devastation could have been far worse; as it currently stands the Japanese National Police Agency has confirmed 14,755 deaths.
The 2004 Sumatra-Andaman tsunami in the Indian Ocean was particularly devastating killing over 230,000 people across fourteen countries, partly because there was no early warning system in place and tsunami awareness was generally very low. Despite this absence a number of people who felt the earthquake in Indonesia and the Andaman Islands moved to high ground, in response to local or traditional knowledge passed down through many generations of those rooted in the area. For these people simple knowledge of tsunamis and understanding their warning signs of an earthquake and a receding ocean proved an effective early warning system by self-evacuating to high ground demonstrating the value of simple education and knowledge.
There appears to be a recurring trend following recent earthquakes greater than magnitude 8.8 that generate tsunamis that inundate coastal communities located near to the epicentre with less than 30 minutes warning. The residents of the Sanriku coast and Sendai in Japan only had 10-30 minutes of warning time before the leading main wave of the tsunami hit, and the earthquake lasted in the region of six minutes, leaving little time to recover and evacuate to higher ground. In 2004, the Indian Ocean tsunami struck Sumatra within 20 minutes of the earthquake killing 168,000 people, when many people were still confused and disorientated by the earthquake. The 8.8 earthquake off the coast of Chile in 2010 generated a tsunami that arrived within 30 minutes in the Valparaiso-Concepcion-Temuco coastline and is responsible for a proportion of the 521 people killed during the event. These instances pose a challenging problem; that even with a sophisticated warning system using the latest technology that can detect an earthquake in seconds and provide a tsunami warning within a couple of minutes, there is often not enough time for potentially affected communities to fully evacuate the tsunami inundation zone.
Two months on from the devastating Tohoku earthquake it has been demonstrated that in most locations the tsunami early warning system was largely effective; mortality rates in the populations in inundation zones in the worst affected areas of Miyagi and Iwate prefectures was less than 10% compared to over 30% for corresponding areas of Arche in 2004. Areas outside the worst impacted areas e.g. northern Iwate, Aomori and Hokkaido the inundation zones were largely evacuated and casualties were very low, with only a few per town, in contrast to the 10% mortality rates as far away as Thailand and Sri Lanka in 2004, demonstrating the preparedness and effectiveness of the tsunami early warning system. It is clear that we cannot fully rely on early warnings to give enough time for everyone to evacuate (including the young, senior, ill, or disabled), however the Japanese tsunami has proved that the most sensible method of coping with rapid onset tsunamis is to focus on being prepared.
It is becoming increasingly possible to forecast where large scale earthquakes may occur and potentially generate a destructive tsunami. By taking preparedness actions such as good land-use planning can be highly effective, for example high schools in towns along the Sanriku coast built on higher ground had high survival rates. In areas of flat terrain where there was not time to evacuate to safety, especially when a tsunami wave is travelling at high speed, tall strong tower buildings (vertical evacuation sites) need to be built that people can get to in time, albeit a costly solution. Whilst some buildings (e.g. port facilities) and their workforces need to be located by the shore, it may be recommended that populations be located on higher grounds, where possible, including the vulnerable populations of a community.
The solution therefore is to work on a case by case basis, understanding the local geography, social and cultural contexts, and economic capabilities to prepare for and respond to rapid onset tsunamis for each and every town, city, or region. This requires significant political will, as to standardise preparedness and warning procedures is the easiest and most cost-effective approach. For rapid onset tsunamis there is no time for hesitation, everything needs to be considered because that ten minutes warning needs to be as effective as possible, otherwise, well you have seen some of the footage.
