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Subsurface map of Delhi
Y. Pandey and R.
Scientists, Central Building Research Institute
247 667, India
Tele: 91-01332-82372/82214, Fax:
the seat of power has been the focus of attention for administrators and
planners. Its fast growing population, natural and manmade disaster proneness,
changing security perceptions and pressure for maximum utilization of space call
for exploring newer avenues for development. Sky scrappers as well as the
sophisticated underground living and working space are the features of
Subsurface maps of Delhi, emerged as an outcome of a
research project undertaken by Central Building Research Institute, are the
essential prerequisite of further urban growth of the mega city. Whether it be
new development of any uninhabited area, delineation of earthquake prone
localities, building up a failsafe corridors creating strategically sensitive
space, subsurface maps are one of the best required tools.
paper, authors discuss about the methodology used for preparation of subsurface
maps as well as their results.
Delhi being the
capital, has always been the seat of power right from ancient times, except for
some decades during the British period. Its strategic geographic location, as
well as the typical geological geomorphological setting makes it so important.
Its importance is to attract people, industrial and strategic establishments in
great proportion, simultaneously converting the mega city into a time bomb being
vulnerable to natural and manmade hazards. It has to expand with faster pace to
cater the growing need, but preparedness to efficiently manage the said
disasters should be seen as imminent urgency by the administrators and planners.
Delhi region falls in zone IV of seismic zoning map of India, which is
located on the margin of Himalayan foredeep. The zone has fairly high Seismicity
with general occurrence of earthquakes of 5-6, a few of magnitude 6-7 and
occasional incidence of 7.5-8.0 magnitude shocks (RITES Report, 1996). The first
recorded major earthquake in this region occurred on 15th July 1720 of intensity
IX (Chandra, 1992; Srivastava & Somayajulu, 1996; Tandon, 1975).
Subsequently other historical events occurred in 1803, 1819, 1905, 1934, 1937,
1945, 1949, 1958, 1960, 1966, 1975, 1980, 1994 during which intensities between
VII and IX are believed to have been experienced as indicated by damage pattern.
During recent times the area has been shocked by a number of earthquakes, out of
these earthquake of 27th August 1960 with magnitude 6.0 and having epicentral
tract between Delhi and Gurgaon was most significant. Recent Himalayan
earthquake namely Uttarkashi and Chamoli were experienced in Delhi, and ultimate
probability of major earthquakes in the region should make the authorities awake
to the problem.
The earthquake history of Delhi region indicates fairly
high Seismicity for the city of Delhi. The most active area of the region is
considered to be the trijunction of the Delhi-Hardwar ridge, Lahore-Delhi ridge
and axis of Delhi folding. Most of shocks are interpreted to be shallow focus
and have concentrated around Sonepat, Rohtak and Gurgaon region in and around
Delhi may be considered as seismically very active and the tectonic elements of
the area are considered capable of generating an earthquake of magnitude 7 on
Richter Scale (Chadha & Mathur, 1995).
Some areas of Delhi, due to
their unique subsurface settings, are relatively more prone to damage in case of
such eventualities. In such cases, apart from the density of population and type
and quality of construction of buildings, thickness of sedimentary deposits play
very critical role. This paper gives an account of CBRI's effort to map Delhi on
the basis of thickness of soil cover, which may be very useful to the common
people, Government and private builders, administrators, planners, rescue
operation managers and many more sections of the society.