__________________, TSUNAMIS ARE SHALLOW-WATER WAVES AND THE RATIO...
24)__________________, tsunamis are shallow-water waves and the ratio between water depth
and the wavelength is very small. The deeper the water, the faster and shorter the wave is. For
example, when the ocean is 20,000 feet deep, a tsunami travels at 550 miles per hour. At this
speed, the wave can compete with a jet airplane, travelling across the ocean in less than a day.
Tsunamis in deep water can have a wavelength greater than 300 miles (500 kilometres) and
a period of about an hour (the period of a wave is the time between two successive waves).
Another important factor in considering tsunamis is the rate at which they lose energy. Because a
wave loses energy at a rate inversely related to its wavelength, tsunamis can travel at high speeds
for a long period of time and lose very little energy in the process.
Offshore and coastal features can determine the size and 25) _____________ of tsunami
waves. Reefs, bays, entrances to rivers, undersea features and the slope of the beach all help to
modify the tsunami as it attacks the coastline. When the tsunami reaches the coast and moves
inland, the water level can rise many metres. In extreme cases, the water level has risen to more
than 15m (50 feet) for tsunamis of distant origin and over 30m (100 feet) for tsunami waves (26)
______________ near the earthquake's epicentre.
Preparing for a tsunami
It is beyond the control of human beings to prevent natural disasters. However, it is certainly
possible to reduce the repercussions, such as loss of life and property, through proper planning.
Government agencies should formulate land-use regulations for a given coastal area with the
tsunami risk potential in mind, particularly if such an area is known to have sustained damage in
the past. Making people aware of the hazards is the key factor in tsunami (27)
_______________. It is important that people have a technical under-standing of the
phenomenon, at least at the basic level; a behavioural response stemming from that
understanding; and confidence in the authorities responsible for issuing a hazard warning.
Repeated false alarms may reduce the alertness and response by the community. Fortunately,
forecasting of tsunamis in recent years has been quite good and the credibility of the Tsunami
Warning System has improved considerably. Forecasting, however, is not an exact science as the
phenomenon itself is complex and data on which the forecast is based may often be inadequate
for certain areas.
Despite modern equipment and communication means, the destruction caused by the 26/12
tsunami was 28) _______________ compared to those in the past. The reason partly lies in the
poor international cooperation and partly in the failure of local governments in handling such
situations. Most of the countries affected by the tsunami had been struck by the fury of the sea
several times in the past. Despite the damage caused earlier, most governments have over-
developed the seashores, destroyed the natural 29) _________________ like mangroves, corals
and other coastal ecosystems and, worse still, allowed large populations to live in the danger
zone.
International Tsunami Warning System (TWS)
The massive destruction caused by the May 1960 Chilean tsunami 30) _______________ a large
number of countries to join the TWS. Another catastrophic tsunami generated by the Alaskan
earthquake of 1964 emphasized the need for an International TWS. Functioning of this system
begins with the detection by any participating seismic observatory of an earthquake of sufficient
size to trigger the alarms, set at the threshold of 6.5 on the Richter scale. The Pacific Tsunami
Warning Center collects the seismic data, locates the earthquake and computes its magnitude.
When reports from tide stations show that a tsunami has been generated which poses a threat to
the population in any part of the Pacific, a warning is transmitted to the dissemination agencies
for relaying to the public. The agencies then implement predetermined plans to evacuate people
from endangered areas. In addition to the International TWS, a number of Regional Warning
Systems have been established to warn the population in areas where tsunami frequency is high.