Tsunami Alerts Lifted after Quake
Reviewed by Hitoshi URABE
Tsunami Alerts Lifted after Quake
"Tsunami" is a Japanese word fairly recently added to the Globalese vocabulary alongside such traditional terms as "sukiyaki" and "sushi," - with full respect to another newcomer "mottainai" promoted by Wangari Maathai, the 2004 Nobel Peace Prize winner and the very first African woman to become a Nobel laureate.
While the term "tsunami" had been well known to those involved in the fields of earth sciences, it became a common word after December 2004, when a tsunami devastated coastlines across south Asia, leaving 230,000 people dead or missing. Technically, a tsunami is not a "wave" in a strict sense; it is a huge mass of water rushing across oceans. It is barely detectable in the high seas. Even the largest tsunamis would show barely a few centimeters rise of water levels in open and deep waters. It is when the water mass approaches land, where the depth of water decreases and coastlines begin to confine the waters the tsunami begins to reveal its deviltry, and that in literally chaotic - as defined in mathematics - manners even the fastest supercomputers cannot simulate.
Japan is prone to attacks of tsunamis - it is a part of life. It used to be that tsunami's were unpredictable in practical terms as much as the earthquakes themselves were. Although the relation of tsunamis to earthquakes had been pointed out since ancient times, because of the scale, which often involves the whole earth, and rareness, in terms of frequency as well as geographical eccentricity, the study of tsunami has advanced significantly only in the recent decades. In addition, it was another huge stride from understanding a tsunami to satisfying the real objective of laying a system to protect lives and properties.
The first phase is to recognize the earthquake. It is necessary to locate the source three dimensionally - where and how deep, and assess the magnitude at the source. Then the possibility of a tsunami and, if likely, its intensity must be assessed. This depends on the depth of water and other factors, such as temperature structure of the water and geography of the seabed. And applying the assessment to real coastlines, not only as how it appears on the map but also, and more importantly, the three dimensional shapes and curves underwater, would provide a vague picture of what might occur. Finally, a decision must be made whether to issue some sort of warning to the public, and if so, of what level - from the extreme of evacuation order to less intense types of warning, alert, and watch, all carefully defined for the authorities and the people to act upon.
Some media reports of last night's incident ran headlines using such expression as "panic." Yes, people were taken by surprise, they hurried to take shelter, and anxieties abound, but apparently there was no "panic." It was a cold and dark night to spend at evacuation centers, but not to a health-threatening extent. It was in fact a well-organized evacuation, timely and calmly done, just as the planners had envisaged.
There were other media reports with such headlines as, "Big quake, big alert, small tsunami." Yes, the quake was big, but it was under the sea scattered about by islets with very small number of inhabitants, causing apparently no discernable damage. Yes, the alert was big, running on all TV channels and radios nationwide, with local police, firefighter, and other officials running about to warn people in areas possible of incurring damages. And yes, the tsunami was smaller than anticipated. While the warning said the water level "could reach" as high as 2 meters, it turned out to be only 40 centimeters. But if the headline had any implication of cynicism, it is worth noting that the headline as quoted above would be definitely better than seeing reports saying "small alert, big tsunami."
The authorities running the tsunami warning system are apparently not satisfied with the last night's performance. Not so much for predicting larger tsunami than what actually came, but the timing in which the warning was issued - 15 minutes after the quake. They say if the quakes occur closer to Japan, and in waters within Japan's jurisdiction where various monitoring systems are placed, the time required from the quake to the sounding of the alarm could be trimmed down to 2 minutes.