Real Risk

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APANESE ARCHIPELAGO

is one of the most vulnerable

countries in the world to tsunamis. A number of monu-

ments and archives have recorded earthquake-caused

tsunamis in different areas in the country since the 7th century.

The most recent massive tsunami occurred in 1993 due to the

earthquake in Southwest Hokkaido, northern Japan, which hit

the small island of Okushiri killing more than 200 people.

Tsunami countermeasures, however, did not fully commence

until the Meiji Sanriku Earthquake Tsunami in 1896, which

caused as many as 22,000 deaths. The traditional countermea-

sure of that time was to carry out total relocation of settlements

from the affected area. This gradually changed to constructed

hardware measures such as embankments and seawalls. It is,

however, not practical to build a structure that blocks the explo-

sive and destructive power of a tsunami, as its height can be

20-30 metres, as observed in the cases of former tsunamis.

Furthermore, any structure would be subject to deterioration

and damage by earthquakes or floods, and would necessitate

huge and continuous financial input for operation and mainte-

nance.

Accordingly, approaches that heavily emphasize lifesaving

rather than countering tsunamis have become popular in recent

years to supplement the limitations of physical countermea-

sures. One such approach was the development of a tsunami

warning system. Due to technical innovations in weather obser-

vation and analysis, the Japan Meteorological Agency now

announces a tsunami forecast within three minutes of an earth-

quake occurring, delivering the information to municipalities

and residents by radio transmission and mass media.

If the forecast urges or instructs evacuation, information about

which areas are particularly at risk, which areas are safe, and

which routes should be taken must be given in advance to the

residents. For this purpose, the preparation of demonstrative

tsunami hazard maps began in the late 1980s. Today, there are

tsunami hazard maps for more than 700 coastal areas, or 40

per cent of the total coastal area vulnerable to tsunamis.

Hazard map preparation, however, does not ensure prompt

and safe evacuation on its own. Kokusai Kogyo, which has been

engaged in a number of hazard mapmaking services with its

outstanding specialist measurement techniques, is attempting

to bridge the gap between hazard maps and evacuation. There

follow two examples of this work.

Computer graphic technology to make hazards visible

As paper-based, simple two-dimensional maps, conventional

hazard maps are not persuasive enough to encourage residents

to prepare for future tsunamis. The question is how to let

people know the real tsunami hazards and how to foster their

‘self-help’ ability, which is required for proper evacuation. To

answer this question, Kokusai Kogyo worked on dynamically

visualizing the propagating tsunami and expanding the inun-

dated area, as part of its hazard mapmaking work for Iwate

Prefecture, which experienced the Meiji Sanriku Earthquake

Tsunami.

Using its high-resolution special measurement techniques,

an airborne laser profiler

and the elaborate analysis of tsunami

phenomena, Kokusai Kogyo simulated the 1896 Meiji Sanriku

Earthquake Tsunami every second for 40 minutes, assuming

that all the existing anti-tsunami infrastructure worked as

designed. Three-dimensional images were displayed via satel-

lite using computer graphic technology. Images were developed

for 13 coastal areas.

The Taro area, in the Iwate Prefecture, is particularly famous

for its tsunami history. After the Meiji Sanriku Earthquake

Tsunami, it was again affected by a tsunami in 1933. This area

alone lost nearly 1,000 residents, and community relocation

was planned. The community leader at that time, however,

resisted by stressing the importance of making the community

resistant to tsunamis, and multiple approaches including the

construction of seawalls and the improvement of evacuation

roads were brought forward.

Due to the time lapse and the fact that Taro was not seriously

affected by the tsunami caused by the Chile earthquake in 1960

as a result of such efforts, the people who had past experience

of tsunami damage became older and the handing down of expe-

rience became difficult. The decreasing number of participants

in the tsunami evacuation drills that had been carried out every

year since 1934 illustrated this, and a decline in people’s aware-

ness was anticipated.

The computer graphic image clearly visualizes the immense

power of the tsunami as it climbed over the seawalls developed

over four decades. The image is often utilized in community

workshop and school classes, and it is expected that individual

preparedness for tsunamis and resolutions to prevent the recur-

rence of the tragedy will be stimulated by this dynamic image.

Hazard map application for tsunami resistant

communities

The preparation and dissemination of tsunami hazard maps

should be merely a starting point. In one case, the map served

as the foundation for community development toward ‘evacu-

ation for all.’

In the tsunami hazard map preparation work for Wakayama

Prefecture, south of Osaka City, which is as active as Iwate

The tsunami hazard map – its role in tsunami

preparedness for individuals and communities

Satoru Tsukamoto, Senior Engineer, Disaster Management Group, Kokusai Kogyo Co., Ltd.