Sunday, Sep 19, 2021

'The Worst Tsunami Could Trigger A 15m Wave In Gujarat'

The vice-president of The Tsunami Society, Honolulu, and an expert on tsunamis, storm surges and tidal waves, on the various challenges that the Indian Ocean Tsunami Warning System poses and the need for coastal inundation maps.

'The Worst Tsunami Could Trigger A 15m Wave In Gujarat'
'The Worst Tsunami Could Trigger A 15m Wave In Gujarat'

Will the Tsunami Warning System (TWS) proposed to be installed in Hyderabad be a part of the larger Indian Ocean TWS?

From the media reports I have read, my feeling is Mr. Kapil Sibal (Union Minister for Science and Technology) is talking of an Indian TWS, which will collaborate with the international one for the Indian Ocean. So the September 2007 goal is for the Indian TWS, and I think they are well on target.

The Atlantic Ocean TWS is supposed to be in place by this year-end. And is it not necessary for the Indian TWS to be part of the larger Indian Ocean TWS?

The Atlantic Ocean TWS involves only two countries, the US and Canada. They are already partners in the Pacific Ocean TWS since 1948, and now they need to involve Europe. Besides, tsunamis in the Atlantic Ocean are local, minor occurrences. However, India has to work with 37 other nations in the Indian Ocean rim.

You have said that the Pacific, Atlantic and Indian Oceans are structurally different and the tsunamis they generate also differ vastly.

The Pacific Ocean triggers 6 to 9 tsunamis a year. However, most of these (but not all) are small with little or no impact. We don’t generally issue a warning when the tsunami is extremely small. Both the Indian and Pacific oceans have tectonic converging plates which generate tsunamis. But the numerical models (on which the warning systems are based) for both oceans have to be very different. After the December 26 tsunami, the Americans, Japanese and Russians-who have worked only on the Pacific system-want to transplant the Pacific Ocean TWS on to the Indian Ocean. That’s okay for the instrumentation, but not okay for the numerical models which are the brain of the system.

The Pacific Ocean is the largest ocean. A tsunami here travels large distances and goes to every corner of the Pacific Ocean; it gets reflected and comes back. But by then, the action is all over. Whereas the Indian Ocean is very small, and is cluttered with islands. Even as the tsunami is under way, the reflected waves begin coming back. For instance, in Kollam, Kerala, the direct tsunami waves alone did not cause all the damage. The waves reflected from Lakshadweep islands also contributed. The Indian Ocean is a semi-closed system where the reflected waves are significant. The Pacific is wide open, where we do not worry [in the warning system] about reflected boundaries. A closed system is very difficult to model-mathematically and physically. We need all kinds of boundary data-about estuaries, rivers, backwaters-in the Indian Ocean. That is why the Indian Ocean TWS takes more time. You can buy instruments and put them, but development of computer models will take some time.

What instruments?

The seismometers that record the earthquakes. The IMD and NGRI may upgrade and enlarge the existing network . I am not aware of these details. Same with the existing tide gauge network which records the tides regularly , but also will record the tsunamis when they occur.

Are you officially consulting with the Department of Science and Technology or the Government of India?

No, I have no official status in India. But I am working with various groups here, as an individual scientist.

Other countries have tapped on your knowledge though…

Yes, Canada, Australia and the USA. In India, I was invited for the first three brainstorming sessions; I am working with the IITs in Delhi and Kharagpur. But I don’t have any official status.

You have spoken about the need for detailed coastal inundation maps to be generated by all the coastal states, and how the TWS would be incomplete without these maps. Of India’s nine coastal states, how many are working on these maps?

I am not aware of the status in every state. The only state I am aware of is Gujarat where I met chief minister Narendra Modi on September 23 at a tsunami workshop in Gandhinagar. I felt that Gujarat is serious in developing procedures to protect its population and coastal infrastructure from tsunamis. I also met the Chief Minister and relief commissioner of Pondicherry on October 25 at their invitation and they also are quite serious about tsunami preparedness. I also was invited by the Indira Gandhi Centre for Atomic Research in Kalpakkam on October 23 where I gave a talk on the numerical models that should be developed to prepare vulnerability maps.

What is the scenario in Tamil Nadu?

No official from TN ever contacted me. So I cannot say what is happening.

But do affected states like TN and AP have the infrastructure to generate comprehensive coastal inundation maps which you have argued are most crucial in countering the damage unleashed by a tsunami?

I do not know… But I am sure they must be doing something about it. I have some idea of what the central government is doing through media reports and by talking with colleagues-they have designated INCOIS in Hyderabad as the Tsunami Warning Centre, and NIOT in Chennai is involved with the instrumentation and modelling; the National Institute of Oceanography in Goa is also involved in the modelling. But I have no idea about what the state governments are doing except Gujarat where I am working closely with Dr. Arun Bapat who is an advisor to Gujarat on earthquake and tsunami issues.

Indonesia has talked about an early warning system which includes seabed sensors to be in place by end-2005. The reaction time will be 10 minutes to the date centre, and from there in five seconds it will reach people. Is this independent of the larger Indian Ocean TWS?

Indonesia is the most affected country in the Indian Ocean.and most tsunamis in the Indian Oceean would start there. So there’s political pressure on the Indonesian government to do something. But when we have 37 countries in the Indian Ocean, we cannot do things overnight.

Should India have seabed sensors?

NIOT and others will decide these issues. The central government institutions are on top of the things. Even if you have all the money in the world, these things take time. The updating of the Pacific Ocean TWS for Canada (that is, the brain of the warning system), which I oversaw, took three years [in the 1990s]. The evidence is that India has moved very swiftly on the TWS, probably faster than anybody else. Others are yet to catch up.

Since the Indian Ocean is more complex than the Pacific, will it take more than three years?

No. As we learn from the past we grow faster. We also have much faster computers now. The generation-propagation models, which I recommend the central government institutions adopt, should take no more than a year from now. And if every state starts today on inundation models, they could all be completed in 18 months.

What does an inundation model tell us?

It tells you the heights of the tsunami waves at each selected coastal location. The public wants to know mainly two things: how high would the waves be, and how far inland would the water come.

In the December 2004 tsunami what was the maximum wave height in India and the maximum reach inland?

I was not directly involved in any tsunami coastal surveys in India. But from what I read in the reports, it did not go beyond 1.2 km inland anywhere. Even in an undocumented case, the maximum it could have gone is 1.5 km. And the maximum wave height was 8 metres.

What could be the worst tsunami waves the Indian coast could witness?

I have examined, irrespective of the size of the earthquake, what amplitude a given coast can support. It varies from place to place. When we look at some of the scenarios for India, the highest amplitude can occur in Gujarat. Even in the worst scenario, the maximum height of waves will be 15 metres in the Gulf of Kutch. It cannot ever go up to 100 m since no coast-given the coastal geometry, ocean bathymetry, land level etc-can support such levels of water, however strong the quake.

To give an analogy, a bucket, however fast the water gushes from the tap, can collect only a specified volume. Similarly, no matter how big the quake, a given area of the coastline can only support a certain maximum volume. The Gulf of Cambay will see a wave of 13 m at best. In Karnataka, Maharashtra and Kerala it can rise to 7m or so. In southern Tamil Nadu, Nagapattinam and Cuddalore, the maximum a wave will rise is to 9 to 9.5 m. In Orissa, the Paradip coast can support a high amplitude (owing to a degenerate semi-diurnal tidal amphidromic point there) of up to 10 m. In Bengal, up to 8 m. In the Andaman, it could go up to 11 m. These are rough calculations I have made; the numerical models will give us a better picture.

How do we factor future tsunamis with data from inundation and numerical models?

You cannot run the models after an earthquake and tsunami happen. All the modelling has to be done beforehand. You model every conceivable possibility from minus to plus infinity. Every parameter-the intensity of a quake, its various epicentral locations, the state of the tide when a quake happens-has to be computed. It will be one model, but you run countless scenarios on it. You synthesise these results and put them into the warning system. So when the real tsunami happens, all you need to do is punch a few numbers-the size of the quake, the seismic moment, epicentre-and the computer will pull out the closest match. Then you use this to warn hundreds of places on the Indian Ocean coast on what the amplitude and inundation would be. I have estimated that a minimum of 87 inundation models will cover the east and west coasts of India as well as the Andaman & Nicobar Islands. A breakdown of this , for example, is 12 models for Tamil Nadu.

How much of the damage to life and property will be reduced with an effective TWS?

Over 95 percent of human lives can be saved, but loss of property-the physical damage-will be there. You cannot stop the tsunami from happening. You can only improve the natural environmental barriers which may help somewhat to reduce the damage.

Can you tell us about the travel-time atlas that has been devised in India?

Many people think the bigger the quake, the faster the tsunami travels. Not true. It only depends on the depth of the ocean. The amplitude of the tsunami depends on the size of the quake, but not its speed. Because we know the ocean depths, we can compute the travel times once and for all. We don’t need to wait for the earthquake to happen. And this is what we have done with IIT Kharagpur as the lead agency. IIT Delhi was involved and so was I. Avijit Gangopadhyay from the University of Massachusetts was also part of the team. We have completed the travel-times for all the 37 countries in the Indian Ocean for 250 locations. On the Indian coast, 49 locations have been chosen.

Travel time from which point of the tsunami’s occurrence?

The travel time atlas works backwards. You choose a point on any coast and work backwards. A tsunami may occur anywhere. Since the contours [of the atlas] are in hours, no matter where the tsunami occurs, you can determine the travel time for a specific point. This atlas should be printed and ready by end of November.


Outlook Newsletters


Read More from Outlook

In CLP Meet, Punjab Congress MLAs Authorise Sonia Gandhi To Name The New CM; Decision Likely Tonight

In CLP Meet, Punjab Congress MLAs Authorise Sonia Gandhi To Name The New CM; Decision Likely Tonight

AICC general secretary and in-charge of Punjab Harish Rawat and two party observers from Delhi-- Harish Chaudhary and Ajay Maken –also participated in the CLP meeting in Chandigarh today.

Inside Kerala’s Pazhur Village – Where Nipah Broke Out And Was Contained

Inside Kerala’s Pazhur Village – Where Nipah Broke Out And Was Contained

A discipline earned while tackling Covid-19 may have saved Kerala from a wide outbreak of Nipah. Despite thin resources, the state health machinery kicked in to put checks in place.

Return Of Campus Life As Colleges Reopen After Long Pandemic Shutdown

Return Of Campus Life As Colleges Reopen After Long Pandemic Shutdown

After befriending gadgets for attending online classes students finally are back to real books and real conversations. Read more education stories in our latest issue.

‘Sidhu Colluded With Pakistan, High Command Humiliated Me’: Amarinder Singh After Resigning As Punjab CM

‘Sidhu Colluded With Pakistan, High Command Humiliated Me’: Amarinder Singh After Resigning As Punjab CM

Former Punjab CM Captain Amarinder Singh said that he will not leave active politics after his resignation, but will decide his new platform after discussing with his supporters.