Dear Sir,
I am enclosing below my article again - this time in text form only.
The article is in the form of an interview.
I would very much appreciate if the article is posted in Goanet
A.A. Fernandes
_________________________________________________________
Gauribidanur seismic array: Is it relevant to tsunami
prediction?
by
A. A. Fernandes
On Sunday 26 December 2004 an earthquake measuring
8.9 on the Richter scale occurred in the Bay of Bengal with
its epicentre just off the coast of Sumatra. A tsunami
caused by this earthquake inundated coastal areas in the
Bay of Bengal taking a death toll of 150,000 people in
India, Sri Lanka, Maldives, Indonesia, Thailand and
Malaysia. An entire Indian air force base was washed away
on Car Nicobar island.
To know more on this subject than has been published in
Indian as well as foreign print and audio visual media,
Simplicius of the Omega Times spoke to Dr. A. A.
Fernandes, scientist at the National Institute of
Oceanography situated at Dona Paula.
Simplicius: What is a tsunami? What causes it?
Fernandes: Tsunamis are long waves in the ocean caused
by natural events occurring in the ocean such as eartquakes,
land slides, volcanic eruptions and impact of meteorites.
Tsunamis can also be caused anthropogenically by
nuclear detonations below the sea floor. In the deep
ocean a tsunami may have a harmless height of one meter,
but as a tsunami approaches the coast; due to the shallow
depth, it can turn into a massive wall of water as much as
100 feet. The first few waves hitting the coast are the
deadliest. The higher the magnitude of the earthquake on
the Richter scale, the larger is the tsunami wave height. As
the Richter scale is logarithmic an increase in one unit of
this scale represents a tenfold amplification of earthquake
intensity.
Simplicius: What is your field of specialization? In what
way is it related to earthquakes and tsunamis?
Fernandes: I am having 30 years experience in NIO
working on ocean waves (period T = 1 to 30 seconds), infra
gravity waves (T = 30 seconds to 5 minutes), astronomical
tide, storm surges, currents and statistical prediction of
paleoclimate. In the last two years I have also been
studying the propagation of Rossby waves and Kelvin
waves. I have expertise in time series analysis, multivariate
analysis and computer progamming in Fortran language.
I got the most job satisfaction working on the determination
of wave direction and wavelength of ocean waves from
array measurements using both computer simulated as well
as measured data. The measured data came from an
operational array at Duck, North Carolina, USA. The Duck
array had an aperture of 280 metres. I have published 5
papers as well as a technical report on my array work
between 1986 to 2002. The same subject also fetched me a
PhD degree in Marine Science from Goa University in
2000 at the hands of Dr. Murli Manohar Joshi. The title of
my PhD thesis is "Study of the directional spectrum of
ocean waves using array, buoy and radar measurements".
My distant familiarity with earthquake directionality and its
location also came through my study of arrays.
Simplicius: You have mentioned different types of waves
that you have worked with in your long career, but you
have not mentioned about tsunamis. How come? Has any
scientist at NIO worked on tsunamis?
Fernandes: At NIO we have upto now been thinking that
tsunamis are a menace affecting Japan and Hawaii only,
therefore requiring no attention from us. The subject of
tsunami crept up only when we were discussing different
types of waves, their frequency and wavelength ranges,
dispersion relation, speed of propagation, restoring force,
causative mechanisms, etc.
Simplicius: What instruments are used for locating the
epicentre and magnitude of an eathquake?
Fernandes: Arrays of seismometers are used for locating
the epicentre and magnitude of earthquakes. The best
known arrays are the medium aperture arrays (aperture =
25 kilometres) installed by the UK in Esklalimuir,
Scotland; Yellow Knife, Canada; Gauribidanur, India;
Warramunga, Australia; and Brazilia, Brazil and the large
aperture arrays installed by the USA in Montana, Norway
and and Alaska. The aperture of the Montana array was 200
kilometres while that of Norway and Alaska was 100
kilometres.
The above arrays of seismometers were deployed in the
early 1960s for monitoring nuclear detonations. It appears
that after our defeat in the Indo-Chinese war in 1962,
Pandit Jawaharlal Nehru gave permission to the USA to
install the Gauribidanur array on the border of Andhra
Pradesh and Karnataka for monitoring China's nuclear
tests. There is a strong likelihood that the location and
magnitude of the Sumatra earthquake reported by Reuters
(Navhind times dated 27 December 2004) was determined
using the Gauribidanur array. It also appears that Indian
seismologists are innocent of the data being collected at
Gauribidanur. Even more foreboding is the fear that the
seismometers available with our seismologists just cannot
measure earthquakes larger than 6.9 on the Richter scale.
Simplicius: Are you suggesting that we do not need any
additional satellites or instrumentation to sound the alert for
a tsunami in the future? Is the Gauribidanur array sufficient
for this purpose?
Fernandes: I am not a seismologist. It is for seismologists
to determine whether the Gauribidanur array is necessary
and sufficient to take care of the tsunami menace. I am just
trying to nudge the discussion on the tsunami towards the
proper direction.
___________________________________________________________
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