NEWS
Seismic microzonation of Jabalpur Urban Centre: An
experiment*
Attempts to develop strategies for earthquake damage mitigation are primarily
borne out of societal compulsions; but these
are also fuelled by the scientific community’s enhanced ability to design and develop programmes to address region-specific
issues. The recently concluded project on
‘Seismic Hazard and Risk–Microzonation
of Jabalpur’ is a commendable example of
how scientific knowledge gets transferred
to the community and prepares it to face up
a calamity that might be waiting to happen.
The multi-disciplinary project on seismic
microzonation of Jabalpur, was initiated by
the Department of Science and Technology
(DST), Government of India and coordinated by some of the leading organizations – Geological Survey of India (GSI),
National Geophysical Research Institute
(NGRI), India Meteorological Department
(IMD), Central Building Research Institute
(CBRI) and the Government Engineering
College, Jabalpur. Various activities in
this project, which started about three years
ago, were steered by a committee set up
by DST under the Chairmanship of H. K.
Gupta, former Director, NGRI, Hyderabad
and currently Secretary, Ocean Development, Government of India.
The two-day workshop on ‘Seismic
Microzonation of Jabalpur’ was attended
by various participants of the project as
well as some invited experts. The exhaustive
report and maps prepared as part of the project were discussed at the workshop. The
end-products of seismic microzonation are
expected to specify the hazard level, in
terms of ground motion at specific locations and these are to be used by those
involved in construction practices, policy
makers and the public, at large. Clearly,
these data products need careful scrutiny,
especially considering their social and
economic implications. That must have
been the prime motivation for the architects
of this project to present the first-cut maps
and reports before a select forum of geologists, seismologists and engineers. Experts
who reviewed the reports and maps gave
their evaluation and made suggestions on
*A report on the workshop on ‘Seismic Microzonation of Jabalpur’ held at NGRI, Hyderabad
during 27–28 September 2004 and sponsored
by DST, New Delhi.
how these could be made more useful for
the practising engineers.
Perhaps, the choice of Jabalpur as the
first city in the country to be microzoned for
the purpose of earthquake-hazard evaluation was made easier by the availability
of a variety of data, including information
related to the moderate earthquake of
1997. Papers presented at the workshop
discussed in detail the methodologies
followed in achieving each of the tasks involved in microzonation and transferring
the information to data products, mostly
in the form of maps. P. S. Misra (GSI),
coordinator of the project, outlined the
methodology followed in various stages
of this project. The procedure, involving
careful integration of a variety of data to
produce maps of different precision levels,
is quite rigorous and these were discussed
at the workshop by the concerned investigators. Geomorphological, geophysical,
lithological, geotechnical and a host of other
data go into making these maps; much of
the basic data that were not available were
collected through field investigations. Vulnerability of structures, classified into
various types, is incorporated to attempt
preparation of a preliminary risk map.
Transferring knowledge from laboratories
to real-life situations always meets with
practical difficulties. Dealing with events
such as the occurrence of earthquakes that
are inherently unpredictable and involving complex near-surface interactions with
built environment obviously calls for a
significant level of preparedness. Some
of the fundamental questions to be addressed in a practical hazard scenario assessment are: which are the potential faults
that are likely to generate future earthquakes and what would be the expected size?
Given that information (assumed in this
study as a scenario earthquake of M 6.5),
the next obvious question is, what type of
ground shaking is expected at a specific
site? How would an RCC or a masonry
structure situated on a rock surface or soil
strata respond to the expected ground
shaking? There are many practical difficulties in constraining these parameters, and
these issues were discussed at length at the
workshop.
Understanding the regional geology and
tectonics of the region is basic to micro-
CURRENT SCIENCE, VOL. 87, NO. 10, 25 NOVEMBER 2004
zonation and the workshop featured detailed
discussions on these issues. What types of
soils are most susceptible to liquefy in the
event of an earthquake shaking, is another
crucial questions. Assessment of liquefaction potential based on field and laboratory studies leading to liquefaction
susceptibility map is another important
step. Work carried out in the project has
led to the generation of a liquefaction susceptibility map, with detailed descriptions on
lithological and geotechnical attributes of
cover sediments. This was an important aspect that was discussed at the workshop.
One of the most important parameters
required in ‘ground characterization’ is
the shear wave velocity of shallow surface
soils. Studies conducted at NGRI have
resulted in generating a shear wave velocity image of Jabalpur. Depth to bedrock
is another key parameter in assessing the
nature of amplification. Images of amplification, likely to be generated by the scenario earthquake, were also discussed at the
workshop. An understanding of the dominant frequencies and peak amplifications is
critical in seismic hazard evaluation and
ground characterization. The response spectrum generated from strong motion record provides this information, crucial for
design of structures. In a region like Jabalpur, for which strong motion data are not
available, one has to depend on appropriate
empirical methods to generate the realistic spectra. Methods to generate more representative spectra were discussed in the
workshop.
Vulnerability of engineered and nonengineered structures to earthquake shaking was another issue discussed at the workshop. This information is essential for
transferring hazard to risk map (the former
showing the expected ground hazard and
the latter depicting the estimated damage
to the built environment) and this part of the
study was conducted by CBRI. The emphasis is on how a specific type of building
(rural, brick, RCC, etc.) is likely to respond
to earthquake shaking, particularly the
dwellings in the urban areas of Jabalpur.
The panel discussion that took place
after the presentations zeroed in on specific
and critical issues, starting with how to
incorporate the suggestions and make the
final products usable for the practising
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NEWS
engineers. Developing the appropriate
methodology is important also for providing better guidelines for similar efforts in
future, for other urban cities in the country.
Admittedly, the efforts for microzonation
of Jabalpur are only a beginning and the
voluminous data generated will help refine the present state of understanding of
the seismic risk in this urban centre. The
methodologies followed in this project,
to be refined with time, will undoubtedly
ease future efforts in this direction.
Kusala Rajendran, Centre for Earth Science Studies, Thiruvananthapuram 695 031,
India.
e-mail: kusala@seires.net
the generation associating its mails with
runners has long passed, runners and boats
still convey mails over 84,000 miles out
of a total of 157,000 miles. The Department disposes of 1,475,000,000 unregistered articles in a year and the number of
complaints received is said to be 1 for every
100,000 articles. This would lead one to believe that the people are averse to complain and that the machinery for receiving
and accounting for complaints needs overhauling.
Owing to the growing needs of the Defence Department in 1942, an extensive
scheme estimated to cost 17 crores of rupees, of erecting telegraph and telephone
channels was put in hand and is scheduled to be completed in 1944–45. The Department was called upon to manufacture
communication equipment in very large
quantities for the Armed Forces. Vast expansion of existing workshops was undertaken
and a new workshop was established in
Central India at a cost of over 30 lakhs of
rupees. Even this was found insufficient
and 91 other workshops large and small
were employed in the manufacture of stores.
The cost of these was Rs 61,95,720 in
1938–39 and it rose to Rs 48,346,000 in
1943–44.
The acquisition by the Department, of telephone systems owned by private companies at Calcutta, Bombay, Madras, Karachi
and Ahmedabad is an event of considerable importance from the point of view
of long-term planning and development.
One can only hope that the red-tape associated with the Government machinery
will not be allowed to impair the efficiency of service.
The Department is run on commercial
basis and it is stated that the increased
rates and surcharges are not a part of Department’s financial policy but are aimed
at raising revenue for the war effort. It is
heartening to note that it is first and foremost a public utility service whose principle objectives are cheapness and efficiency.
One would in this connection suggest the
grant of a bonus to the workers out of the
profits, or the introduction of co-operative
principles in any other form so that the
workers may feel that they stand to benefit both by economy and efficiency.
FROM THE ARCHIVES
Vol. XIII]
OCTOBER 1944
[NO. 10
The Department of Indian Posts
and Telegraphs
An unofficial publication describes the story
of communications as set against a background of vast distances, varying climatic
and geographical features, of hundreds of
languages and dialects, of illiterate persons who have incomplete addresses written out for them, of 400 million people,
more than 85 per cent of whom live in
700,000 villages, of how one-fifth of the
human race spread over an area as large
as Europe, excluding Russia, keep in touch
with one another. It is learnt that though
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CURRENT SCIENCE, VOL. 87, NO. 10, 25 NOVEMBER 2004