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Earthquake
Vulnerability
Not only
because of difficulty in predicting time, location
and manner of strike, but also due to its
destructive nature causing huge loss of lives and
property within a few seconds, the earthquake has
been categorised as the single most destructive
natural hazard. Moreover, it has crippling
adjunctive effects such as landslides, flooding,
erosion and fire disasters. A single earthquake can
cause damage to a nation that is equivalent to over
5% of its Gross National Product [GNP], kill
thousands and make millions home and property less.
The combination of advanced science and technology,
more coordination among various agencies [public and
private as well as national and international] and
increase in research and publications on earthquakes
has dramatically reduced the damages in developed
countries whereas this trend is in the opposite
direction in the case of developing nations. People
living in these regions are becoming more vulnerable
and socio-economic losses from earthquake disasters
are on the rise.
Earthquake hazard in Kathmandu is due to four major
geophysical processes. First, Kathmandu [and Nepal]
lies in an active earthquake belt between the
Tibetan and Indian plates. According to Bilham
[1995, 1999] based on a recent study on plate
movement in the Himalayas of Nepal, India is moving
north-east at the rate of 58 mm/year and southern
Tibet is shifting towards the south west at the rate
of 36 mm/year resulting in shortening of Nepal by
2cm per year [Figure 1a] thereby developing stresses
in the ‘Main Central’ active fault, ‘Mahabharat’
thrust and ‘Main Boundary’ active fault. Second,
Kathmandu [and the whole Valley] comprises of many
active fault lines particularly in the western and
southern parts [Figure 1b]. Third, the floor bed of
the Kathmandu Valley is still soft, made up of the
drained lake in pre-historic times. It is believed
that Kathmandu’s geological development took place
around one million years ago in three phases [Figure
1c] - (i) 200 m thick sediment on the rock bed
during the five hundred thousand year (ii) about
200m to 300m thick special type of clay deposit
during the following five hundred thousand year and
(iii) about 20m thick mixture of clay and sand
deposit during the next fifty thousand year. This
type of soil has low bearing capacity, is prone to
flooding and land slides, and exhibits high
amplification against seismic waves.
Lastly, Kathmandu has been affected by numerous
earthquake events in the past. The present knowledge
on seismology states that there is a great chance of
recurring earthquake event in the area that has been
hit by past earthquakes after a certain interval
depending on the magnitude of earthquake [Table 1].
According to the seismic record of the last two
centuries, an earthquake of magnitude eight on the
Richter Scale hit Nepal two times at an interval of
nearly a hundred years. A recent study on the
movement of tectonic plates and analysis of the
history of Himalayan earthquakes has concluded that
a great earthquake is due, which would be in the
‘Central Gap’ of Himalaya of Nepal, affecting
Kathmandu.
Earthquake disaster is the result of the interaction
between a Hazard (Physical Event) and a Vulnerable
Society (Social Event). Therefore, Earthquake Risk
is the product of Hazard, Vulnerability and
Exposure. While nature provides equal opportunity
for all, it is the process of urban development
under a given legal and institutional framework that
is responsible for unequal distribution of resources
and socio-economic disparity. Hence the same
intensity of seismic risk can have different impacts
on society and settlement, depending on the urban
patterns, socio-economic status of the community and
level of preparedness. A natural hazard cannot be
changed but modification on the societal part, i.e.,
Vulnerability and Exposure, through designing
earthquake-resistant structures, enhancing capacity
of individuals and cities through preparedness, and
raising community awareness, can dramatically reduce
the damages from earthquake disasters. However, the
decision makers involved in urban growth management
in particular and the common people of the society
in general are yet to acknowledge this. The failure
to regulate haphazard urban growth and building
transformation has numerous consequences on
intensifying earthquake vulnerability in Kathmandu
in different ways.
First, the process of urban transformation –
replacement of 3-4 storey traditional residential
buildings by 6-7 storey concrete buildings for
commercial use without upgrading the existing
infrastructure capacity in the historic core areas
and the urban sprawls of ‘low rise low density’
individual house constructions in the peripheral
agricultural land without provision of even basic
amenities - let alone emergency facilities - has
been carried out on ad-hoc basic with piecemeal
process in the absence of a comprehensive master
plan and without development controls. The need of
integration of earthquake mitigation components and
techniques into urban layout plan and building
construction is hardly realised in the planned
developments – land pooling, site and services,
housing construction – implemented by both the
public and private sectors.
Second, many unregulated industrial establishments
as well as commercial complexes are mushrooming in
the dense residential areas irrespective of the
existing infrastructure capacity thereby generating
a new set of urban problems of traffic jams,
infrastructure degradation and, above all, exposing
higher percentage of people under the seismic risk.
Huge built form, high density and traffic congestion
will cause emergency rescue and relief operation
difficult in such areas in case of a big earthquake.
Third, the present trend of vertical division of
traditional building stocks and their haphazard
renovation and reconstruction – creation of new
openings haphazardly on the load bearing front
walls, provision of toilets and staircases in the
divided part by destroying the part of the existing
structure, and addition of habitable rooms by either
converting the ground floor to a room, removing
significant parts of the load bearing walls or
adding new floors often of different materials,
floor height and construction techniques on top of
existing buildings – goes on unabated [Photo 1a, b].
This whole process of rebuilding - formation of soft
storeys, discontinuity in load transferring system,
lateral stiffness and strengths resulting in
torsional effect, creation of ‘Pounding Effect’ due
to differences in floor and building heights,
material and construction technique in adjacent
buildings – has not only further weakened these old
buildings against seismic forces but has also
converted the narrow pedestrian lanes, street
squares and courtyards into parking lots, garbage
dumping sites, and, above all, into ‘death traps’
[Photo 1c, d].
Fourth, new settlements in the peripheral areas are
also not safe against an earthquake as they often
comprise of many building structures built by
inappropriate and informal methods - road layouts of
inadequate width and insufficient space for
vehicle-turning, thus making the entry of fire
fighters and ambulances impossible in an emergency
situation, and lack of open spaces and other social
amenities, needed for rescue and relief operations
[Photo 2a]. The new trend of building construction -
generally five and half storey height with soft
storey on the ground, three-foot projections from
the second floor onwards, and often characterised by
‘weak columns and strong beams’ and ‘short column’–
on the one hand, and the decorating of façades with
‘false’ architectural elements - double columns, bay
windows, sloped roof, etc. - is adding new
vulnerable urban structures in the city [Photo
2b,c]. Such structures are dangerous not only for
those who occupy the buildings but also for
pedestrians in the vicinity. Lack of quality control
on construction work [Photo 2d] and building
materials, wrong detailing of bars in slabs and
columns and absence of supervision on the site by
trained technicians have further weakened these new
buildings.
Fifth, numerous educational institutions as well as
private nursing homes, are running their activities
in ordinary residential buildings, built by informal
process. These critical facilities and ‘mass
gathering’ buildings used as ‘evacuation shelters’
as well as ‘mass treatment centres’ during an
emergency must have high safety factor based
designs. However, in the case of Kathmandu, they are
the first to be hit by an earthquake. Sixth, many
urban poor of slums and squatter settlements
residing along river banks and children and women
engaged in local factories, restaurants and in
private houses as servants are highly vulnerable not
only because they are living and working in
hazardous sites but also due to their illiteracy and
lack of funds to assist in their recovery. Children
below fifteen [one third of Valley’s population] and
elderly above sixty-five are also vulnerable due to
impaired mobility and inability to withstand trauma
during an earthquake.
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