Tsunami Surveillance System (TSS) – A Global Necessity
Murugan Sham Raja.
Prasad Vara Lingam.
Symbiosis Institute of Geoinformatics
- A brief methodology of Developing a reliable Tsunami Surveillance System and the Impact Assessment study for the Tsunami which had occurred on December 26, 2004.
A high-magnitude earthquake, 9.0 on the Richter scale, struck southern Asia at 00:58 UTC, 6:58 AM local time. The epicenter was 320 km west of Medan, just off the west coast of the Indonesian island of Sumatra. The earthquake was followed by series of tsunamis that killed over 175,000 people, mostly in Indonesia, Sri Lanka, and Southern India. The coastal regions of India, Sri Lanka, Thailand, Indonesia, Maldives, Malaysia, and Myanmar were all severely affected.
Despite the reduced travel times, an extant early warning system could have saved tens of thousands of lives. Notwithstanding the relative paucity of major tsunami events in the Indian Ocean, it is critical that the most is made of the current window of opportunity to establish an effective Tsunami Surveillance System for the basin. There is some evidence of the clustering of major quakes in the region and a possibility that another large; tsunamigenic event could arrive within decades rather than centuries. The technology required: a system of ocean-floor pressure sensors linked via satellite to provide tsunami warnings to emergency managers in the countries at risk – is well established in the Pacific region. More critical to the successful operation of a warning system is an effective means of rapid dissemination of the warning with a well supported Disaster Management Group to the population at risk.
With the advent of technological advances in the fields of Remote Sensing, Geographical Information System and Global Positioning System- a reliable Tsunami Warning System coupled with an effective disaster management system can be developed.
This paper explains the methodology of developing Tsunami Surveillance System and the Impact Assessment for the Tsunami which had occurred on December 26, 2004 has been studied. The immediate need for Tsunami Warning System has also been addressed.
Tsunamis are ocean waves produced by earthquakes or underwater landslides. The word has originated from Japanese Language and means “harbor wave,” because of the devastating effects these waves have had on low-lying Japanese coastal communities. Tsunamis are often incorrectly referred to as tidal waves, but a tsunami is actually a series of waves that can travel at speeds averaging 450 (and up to 600) miles per hour in the open ocean. In the open ocean, tsunamis would not be felt hundreds of miles long, with amplitude of only a few feet. This would also make them unnoticeable from the air. As the waves approaches the coast, their speed decreases and their amplitude increases. Unusual wave heights have been known to be over 100 feet high. Tsunamis are most often generated by earthquake-induced movement of the ocean floor. Landslides, volcanic eruptions, and even meteorites can also generate a tsunami. As a tsunami nears the coastline, it may rise to several feet or, in rare cases, tens of feet, and can cause great loss to life and property damage when it comes ashore. Tsunamis can travel upstream in coastal estuaries and rivers, with damaging waves extending farther inland than the immediate coast. A tsunami can occur during any season of the year and at any time, day or night.
A tsunami is different from normal waves on the ocean. Wind-made ocean waves cause the water to move down to about 150 meters at most. In contrast, the passage of a tsunami involves the movement of water all the way to the seafloor. This means that the speed of a tsunami is controlled by water depth - as the wave approaches land it reaches increasingly shallow water and slows down. Compared to the front of the wave, the rear is still in slightly deeper water (so it is going slightly faster) and catches up. The result is that the wave quickly 'bunches up' and becomes much higher. The highest tsunami occur if they encounter a long and gradual shallowing of the water, because this allows enough time for the wave to interact with its surroundings and cause extensive damage to low-lying areas.
As tsunami run up onto land and bounce around, energy is dissipated through often destructive processes. Eventually energy is fully dissipated and the sea is restored to its normal state of equilibrium.
To develop an Efficient Tsunami Surveillance System which predicts the travel time of potential Tsunamis by monitoring the ocean floor and warns the disaster management system operating on land in real time to minimize damage of life and property.
The methodology in developing a Tsunami Surveillance System consists of the following stages:
Figure 1.1 Scheme for developing Tsunami Surveillance System
2.3.1 Identification of Seismic Zones:
The first step in mapping of risk prone areas is identification of seismic zones and study of the plate tectonics in those areas. The study area has to be categorised and mapped according to the seismic zones. There are five seismic zones named as I to V as details given below:-
Coastal areas less than 20 m high above mean sea level have to be identified and merged with the above seismic zone map using GIS Software. For example the low lying areas in the recently occurred Tsunami are shown in figure 1.2.
2.3.3 Generation of Travel Time Maps:
Travel time is the time taken for a Tsunami to hit the shore from the epicenter of the Earthquake. Travel times for different Earthquake intensities are required for the Disaster Management Team to readily plan their rescue operations. For example, Travel time for the recently occurred ‘Tsunami – South East Asia’ has been mapped in figure 1.3.
Figure 1.2 Map of Low lying Areas – South East Asia
Figure 1.3 Travel Time Map of Tsunami – South East Asia
2.3.4 Identify points on ocean floor wherein Sensors can be planted:
Suitable positions on the ocean floor have to be identified for positioning the sensors that detect the change in ocean currents. These points must be uniformly distributed over the ocean floor for which the Tsunami Surveillance System is developed.
2.3.5 Location of Command Centers:
Command Centers are locations on risk prone areas wherein the information of a natural disaster viz Tsunami with their respective Travel Time is disseminated. The command centers immediately report to the Disaster Management Team involved in Rescue and Relief Operations.
2.4 Risk Analysis for Damage Control
2.4.1 Study of Tsunami – South East Asia:
Information relating to the submarine earthquake in between Aceh, Indonesia and Sri Lanka of the 26th of December, 2004 has been compiled here. This compilation archives much of the readily available scientific information.
A comprehensive study of the event before and after occurrence, in this case Tsunami has to be carried out to asses the impact of damage in terms of Life, property and Geography in the affected areas. Remotely Sensed Spatial Data obtained from Satellites with greater coverage area aids in Impact assessment as well as incessant monitoring of the Risk prone areas. Satellite imagery of Tsunami occurred on 26th December is given in figure 1.4.
2.4.3 Extent of life and property loss:
The Extent of Life and Property loss has to be assessed for an occurred event and the distribution of population along the risk prone areas have to be mapped for Damage control measures.
2.4.4 Estimate impact on economy:
The impact of an occurred event on the economy of the nations affected has to be estimated so that the development plans for the affected areas due to a natural disaster can be worked out. Reconstruction of the economy depends upon study done on the impact assessment of the economy.
2.5 Simulation and Impact Assessment
2.5.1 Creation of DEM model wherein event had occurred:
Digital Elevation Model – DEM is a representation of elevation values helps us in identifying the areas which will be inundated due to occurrence of a Tsunami. The Disaster Management Team can identify higher elevation points and can evacuate the people in case of emergency.
2.5.2 Simulate the impact for all risk prone areas:
In running a "simulation", conditions for a hypothetical triggering event are input to a computer model, and then the model is allowed to run or compute the changes in sea level that would be triggered over time. The outputs of these calculations are often output as pictures or "visualizations" so we can see what might happen.
3.1 Detection of Tsunami
Tsunami monitoring is done using detection equipment set on buoys and the seafloor. One method of detection involves checking the varying pressure of water as waves pass overhead. When sensors detect pressure variations that are abnormal, i.e. not in the normal range for passing wind waves, tides or storms, tsunami warning plans go into effect. Current instruments are able to detect abnormal pressures equivalent to the height of 1 cm of water. Even killer tsunamis are difficult to detect as they move across the open ocean. Sensitive instruments are required because passing tsunami affect sea level by about a meter over wavelengths that are tens to hundreds of kilometers long. Sensors may make the pressure measurements, but the data must also be processed to sort things out. Sensors deployed on the bottom of the ocean transmit data in practically real-time to inquiring minds on land. Underwater sensors are linked to buoys at the sea surface that transmit to satellites. From there, information travels as fast as a phone call to wherever people decide it is needed. Once they have data from observations at sea and combine it with other relevant information, people along the command centers of tsunami surveillance systems.
3.1.1 Data collection from sensors:
The reading from sensors deployed on the bottom of the ocean floor is transmitted to land through satellites in real time. Sensors provide us with pressure measurements that have to be processed to obtain useful data.
3.1.2 Data analysis using the reading:
The transmitted data has to be processed and analyzed for any changes. Any deviation from normal reading has to be immediately analyzed for occurrence of Natural disasters.
3.1.3 Information dissemination (warning) to command centers:
Warning has to be given to the risk prone areas and the information has to be disseminated to Disaster Management Team for immediate rescue operations.
4. Disaster Management System
Though it is not possible to avert natural disasters, the suffering and misery due to loss of life and adverse socio-economic impact can be minimized by human innovations. Nowadays Disaster Management System plays a pivotal role in minimizing life and property loss by strategic planning for rescue operations. Some of the properties for a reliable Disaster Management System are discussed below.
Tsunami – South East Asia which occurred on December 26th, 2004 destroyed many lives and property, a warning in time could have saved many lives. The methodology for a reliable Tsunami Surveillance System has been discussed and the need for the same is addressed.
I am grateful to the faculty and management for their guidance and facilities provided in bringing out the paper. I owe a great deal to my fellow batch mates for their constant support.
Inspired by “Cover Story Exclusive by His Excellency Dr A.P.J. Abdul Kalam”, The Week dated 9th Jan, 2005.