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Seismic Hazard and Vulnerability in the Built Environment of Chennai City, India

G.P Ganapathy

Centre for Disaster Mitigation and Management, VIT University, Vellore 632014, India

seismogans @yahoo.com

A. S Rajawat

Space Application Centre, ISRO, Ahmedabad 380015, India

asrajawat@sac.isro.gov.in

S.K Sekar

Centre for Disaster Mitigation and Management, VIT University, Vellore 632014, India

sksekar@vit.ac.in

Abstract

Seismic vulnerability in urban areas is the biggest and most rapidly growing problem in developing

countries. India has highly populous cities and majority of the construction in Indian cities are not

earthquake resistant. Chennai city is one of the well urbanized and densely populated areas of India,

where the majority of buildings are reinforced concrete cement structures containing three to four

stories. Also the city is listed under GOI-UNDP Earthquake Vulnerability Reduction Programme as

one among the 38 urban centres which have more than half million population in India. The Bureau

of Indian Standard categorized the city under Seismic zone III (prone to moderate seismic hazard -

can expect earthquake magnitude upto 6.9 in this zone). Geologically major part of the city is

covered by Recent alluvium to a maximum thickness of 28m and these alluvial deposits can amplify

in multi-fold during earthquakes. The damage caused by the past earthquakes in the country

reiterates the scale of vulnerability of built environment. Such being the case, safety of the city is

extremely important to safeguard the built environment and infrastructures from the earthquakes.

The present paper aims to study and understand the vulnerability of the Chennai city‘s built

environment and infrastructure due to earthquakes. The seismic hazard of the city is assessed by

integrating geological and geotechnical parameters in GIS platform. A pilot seismic vulnerability

study is carried out in the densely populated built areas of the city. A first level rapid visual

screening study of buildings is carried out for part of the area. The vulnerability on infrastructure

viz., road, railway line, bridges, underground pipelines are mapped using GIS techniques. The

seismic vulnerability of part of the city is quantified by integrating the seismic hazard over the built

environment and infrastructure details. The out come of study will be helpful in all cases where the

vulnerability is assessed to be high, detailed investigations may be required for seismic evaluation of

buildings & infrastructures for retrofitting and further building usage purposes.

Keywords: Geotechnical, Seismic Hazard, Vulnerability, Built Environment, Chennai City.

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1. Introduction

Sustainable urban development is one of the most pressing challenges facing the human community

in the 21st century. The world‘s urban areas are now home to nearly half of humankind (UNCHS,

2001). From the last 50 years, urban areas, particularly in developing countries have experienced

unprecedented growth. Urban areas today account for 35% of the total population of 3515 million. By

2025 the majority of the regions of world population will live in urban areas. In India the degree of

urbanization is at 27.8% in 2001 and it is anticipated that 50% of population would end in urban

areas by 2021 (Ved Mittal, 2009). Post disaster studies, especially after the Bhuj earthquake, have

given the engineering community both architects and structural engineers number of important

lessons to be adequately addressed so as to mitigate the effect of such hazards in future (Shailesh

Kumar Agrawal and Prasad, J.K, 2009). Chennai city has experienced three earthquakes of

magnitudes greater than or equal to 5.0 in 1807, 1816 and 1823 (Ganapathy 2005). Also part of

Chennai falls in seismically moderate to high hazard prone areas (Ganapathy 2011). Urban areas

likes Chennai city therefore require special consideration during the evaluation of seismic hazard and

vulnerability. As a result, even relatively moderate earthquake events can be the source of huge

socio-economic disasters. Assessing the seismic hazard and vulnerability is an important tool to

reduce the earthquake risk. In this regard a study on quantification of seismic hazard vulnerability of

the built environment, critical facilities, and lifeline utilities of Chennai city.

2. Description of the Study Area

Chennai formerly known as Madras is the capital city of the Indian state Tamil Nadu covering an area

of 174sq.km. The district is bounded by north latitudes 120 59‘ 10‖ to 13

0 08‘ 50‖ and east longitudes

800 12‘ 10‖ to 80

0 18‘ 30‖ (Figure 1). It has the second largest beach in the world stretching more

than 12km length. The population of the city was 4.343 million in 2001 and projected to 5.343

million in 2011 Census of India (Census, 2001). Chennai being the fifth most populous city in India,

it is also the world's 36th largest metropolitan area. The Archaean crystalline rocks, Gondwana &

Tertiary sediments and Recent alluvium are the three group of geological formations found in

Chennai. Most of the geological formations are concealed since they are overlain by the alluvial

materials excepting for a few exposures of crystalline rocks of Charnockites in south-western part of

Chennai (CGWB Report, 1993). Ground shaking is more severe on sites underlain by thick deposits

of saturated sediments rather than those located on bedrock. As a result unless precautions are taken,

the greatest loss from ground shaking where the structures are built on thick relatively soft, saturated

sediments (UNDRO - 1, 1978). Chennai city is in such condition, about 80% of the city located in

the recent alluvial material and buildings constructed in these areas would be highly vulnerable to

earthquakes.

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Figure 1. Location map of Chennai city

3. Approach

To understand the Seismic Hazard and Vulnerability of Chennai City a pilot study is carried out on a

regional scale of 1:12,500. The seismic hazard of the city is assessed by Analytical Hierarchy

Process (AHP) technique developed by Saaty in 1980. The thematic layers viz., Peak Ground

Acceleration (PGA), soil, geology, groundwater fluctuation and depth to bedrock are prepared in a

GIS platform. A pair wise comparison matrix was prepared for these five thematic layers. Following

the AHP, the thematic maps are assigned weights on a scale of 1–5 depending on their contribution to

seismic hazard. The higher weight is assigned to the theme that contributes more to the hazard. The

obtained values are then incorporated in Arc-GIS Spatial Analyst tool for the integration of all the

thematic maps to obtain the seismic hazard microzonation map of Chennai city. The UNION and

overlay operation carried out to integrate these five thematic layers.

To understand the vulnerability of the built environment and infrastructure, a spatial/non-spatial

database on the built environment, critical facilities, transportation and lifeline utilities was created

for the Chennai city. These elements at earthquake risk were studied for different level of

vulnerability in the seismic hazard zone. The steps involved in the vulnerability assessment are

identification of high risk areas by integrating the seismic hazard map over the vulnerability map and

the focus the vulnerability assessment on areas and or structures located in the high risk areas. The

quantification of seismic vulnerability of Chennai city is assessed by integrating seismic hazard map

over the built environment and critical facilities, transportation and lifeline utilities, in a GIS

platform.

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4. Seismic Hazard and Vulnerability of Chennai City

4.1 Seismic Hazard of Chennai City

The city has been classified under Zone III (moderate seismic hazard) as per seismic hazard map of

India published by Bureau of Indian Standard (BIS, 2002). A first level seismic microzonation map

of Chennai city has been produced with a GIS platform using the themes, viz, Peak Ground

Acceleration (PGA), Shear wave velocity at 3m, Geology, Ground water fluctuation and bed rock

depth. Chennai has been broadly classified into three zones, as high, moderate and low in terms of

seismic hazard in an event of future earthquakes (Figure 2).

Figure 2. Seismic hazard of Chennai city

The part of Chennai falls in seismically moderate to high hazard prone areas. The resultant map

depicts that the high hazard areas are distributed in patches around Adyar River and few patches

distributed below Cooum River in the south western part of the city. The areas in the southern part of

Chennai represent lacustrine deposits are underlined by marine black clay as evident in Taramani

areas. The maximum depth to basement is 14m. The central part of the city has mainly fluvial origin

of flood plain deposits as evidence from the flowing Adyar and Cooum rivers. The upstream portion

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of Adyar and Cooum rivers had a moderate slope and in the down stream, the rivers are very gentle to

flat in coastal areas. These areas in the northern part of the city represent black clay and alluvium of

marine origin with maximum depth to basement of 30m and patches of these areas show high hazard.

The western and northwestern part of Chennai falls under moderate hazard. These areas represent the

shale and clay of the Gondwana age and are also correlated with lake fill deposits. The remaining

areas are prone to low seismic hazard. It can be concluded that half of the Chennai city is prone to

moderate to high hazard.

4.2 Vulnerability of Chennai City

Establishing the degree of vulnerability of buildings and lifeline utilities, one can obtain an estimate

of risk. Vulnerability analysis is, therefore, an intrinsic aspect of disaster mitigation and one of the

linkages in the assessment process (UNDRO-2, 1991). The Chennai city‘s vulnerability is assessed

in three categories viz., built environment, critical facilities (essential and high potential loss), and

transportation & lifeline utilities.

4.2.1 Built Environment

Once the seismic hazard has been quantified, the next step is to create a spatial representation of the

study areas structural, demographic, and economic inventory. Large scale base maps were prepared

using satellite images in GIS platform. The creation of building database for the present study will be

based on visual interpretation of satellite imageries/aerial photos and field inventories. A spatial data

base on landuse, road, railway, bridges, water ways and built environment were created in a GIS

platform using the collected maps from various authenticated agencies viz. Census of India, Chennai

Metropolitan Development Authority (CMDA), and Corporation of Chennai.

In the Second Master Plan published by Chennai Metropolitan Development Authority (CMDA

2008), the landuse of Chennai in the year 2006, the residential areas covered by 54.25 %,

institutional areas 18.48%, commercial areas 7.09%, industrial areas 5.17%, open space 2.09%,

agriculture and non-urban areas 0.57 & 0.47, and the areas including vacant, forest, hills, low-lying

areas and water bodies etc, are 11.89%.

Chennai (Madras) in 1600 was formed of scattered settlements separated by long distances. The

population, which was 19,000 in 1646, expanded to 40,000 in 1669. The surroundings of the Fort

area covering nearly 69 kms and containing within it 16 hamlets were constituted as the City of

Madras in 1798. Later on the city extended over an area of about 70 sq.kms and had a population of

5.40 lakhs in 1901. The population of the City increased to 8.6 lakhs by 1941. The city occupied an

area of about 80 sq.km and its boundaries have been extended in 1923. The thirty years between

1941 and 1971 saw tremendous growth in population and economic activity in and around the City.

The population first passed the million marks around 1943 and then doubled itself in a short span of

about twenty years to cross, the two million mark. In 1950 the boundary of the City was extended to

cover 129sq.km. The west of Nungambakkam was covered by the Nungambakkam Tank and this

long tank extended in the form of a crescent for nearly 6 kms covered the west of Nungambakkam,

and was disappeared after 1950‘s covered by settlements. The present Chennai is 174 sq.km areas

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with a population of 43.43 lakhs and projected to 53.53 Lakhs in the year 2011 as per Census of

India. The population density of the city is 25000/sq.km approximately. The details of urbanisation

from the year 1633 to 2006 are presented in the Figure 3.

Figure 3. Map showing the spatial growth of urbanisation in Chennai from 1633 to 2006.

Census 2001, reveals the different wall material of the constructed buildings are Brick 65.03%,

Concrete 21.78 stone walls 5.16% and rest of the buildings walls constructed by Wood, Mud,

Unburnt brick etc. In the city 75% of the houses are with roof made up of brick, stone, concrete and

other materials of pucca nature. About 15% are with semi-pucca roofing materials such as tiles, slate,

G.I. metal sheets and asbestos cement sheets, and about 10% are with ‗Katcha‘ materials such as

thatched, bamboo etc. Totally 75, 498 slums in the city. Among these 30,922 slums distributed along

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the river margin, 5,288 in feeder canals, 22,769 in road margin, and 16,519 distributed in seashore

areas. Three major watercourses in the Chennai City viz, Cooum River, Buckingham canal, Adyar

River which are encroached by 30922 slums viz., 8,432, 15,733, and 6,757 respectively.

4.2.2 Critical Facilities

The classification given in HAZUS-MH, 2010 is used for the present study on critical facility

analysis, Transportation and Utility lifeline structures. The critical facilities are classified in to two

categories viz, essential facilities (hospitals, medical clinics, schools/educational institutions, fire

stations, police stations and emergency operations facilities) and high potential loss facilities (dams,

levees, military installations, nuclear power plants and hazardous material sites). The details of

critical facilities are presented in the Figure 4.

Figure 4. Spatial distribution of critical facilities in Chennai

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Chennai is well known for educational institutions totally 1585 institutions (schools, colleges,

technical educations, medical education, veterinary college, Law College) and most of these

institutions were spread spatially in the southern side of the city. Out of 1585 institutions, 485 are in

Government and Government aided and other 1100 are private category (Census 2001). Chennai has

totally 323 hospitals which includes 28 Government Hospitals and 42 private hospitals and had a

capacity of 12,522 beds and 8411 beds respectively. Apart from this totally 25 fire stations, 96 police

stations, and 10 information & publicity bureaus are available in the Chennai city (Yellow Pages,

2011).

4.2.3 Transportation and Lifeline Utilities

The lifeline inventory is divided between transportation and utility lifeline systems in the Hazus

Methodology. The transportation systems include highways, railways, bus, ports, ferry and airports

and utility systems that include potable water, wastewater, natural gas, crude & refined oil, electric

power and communications. The transportation details and Lifeline utilities are given in Figure 5

Figure 5. Spatial distribution of transport network and lifeline utilities in Chennai

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The Chennai city‘s road network is mainly dominated by radial pattern and it converging towards

George Town and is the main Central Business District (CBD) of the Chennai Metropolitan

Authority (CMA). The city‘s road network is categorised as national highways (3 Nos) and a number

of radial roads which connects CMA. The railway network of Chennai carry‘s by 3 corridors in

northeast southwest direction as well as in east to west direction and almost covers the total city. The

Phase 1 & Phase 2 of MRTS traversing a length of more than 15 km covering the residential and IT

corridor on the south eastern side of the city in addition to those 3 corridors.

Chennai city‘s sewerage system was designed in 1910 for an estimated 1961 population of 6.6 lakhs

at the rate of 114 lpcd, as a separate system. The system then allowed for admission of storm water

from house courtyards and roofs through gullies. The city was divided as north, west and south

(independent) drainage areas. In the present Chennai City Corporation area of 174sq.km the

sewerage system now covers 99% of the city area. There are 5,15,560 sewer connections as on date to

serve the population of Chennai City through a network of 2,663 kms of sewer and 180 sewage

pumping stations. The city has one Airport and sea port. The total quantity of exports handled by

sea port remains larger when compared to imports. Chennai has a major harbour, which consist of

209 acres. Apart from these 9 electricity offices, 17 fuel stations, 97 gas appliances/agencies, 47

telecommunication services and 106 water suppliers are in the Chennai city (Yellow Pages, 2011).

5. Discussions

The Chennai city has been classified into three broad zones, viz, High, Moderate and Low Seismic

Hazard. The High seismic Hazard concentrated in a few places in the western central part of the city.

The moderate hazard areas are oriented in NW-SE direction in the Western part. The southern and

eastern part will have low seismic hazard. Out of 174 sq.km area 107.68 sq.km area covered by

residential and commercial buildings. Most of the residential and commercial areas fall under

moderate to high seismic hazard areas. The urbanization in the city starts from north and spreads in a

radial pattern. The areas around Saidapet, Kodambakkam and Anna Nagar are densely populated as

well as these areas built over the recent alluvial materials, which have the capacity of the soil

amplification 2 to 3 times more than the normal soils. These areas are falls in high seismic hazard

zone and mostly residential. T.Nagar is one of the centres of attraction in Chennai for shopping and

mixed residential areas, where most of building have spatial irregularity. These are highly vulnerable

during earthquakes. This area also falls under moderate to high seismic areas. Nearly 77% of the

buildings are accessible through tar roads, and only 14% are approachable through mud roads. 18%

of the buildings comprise flats and 41% are independent buildings. Since the city is old one, totally

147 heritage buildings are spreader mostly in the north Chennai, where we have moderate seismic

hazard. The north Chennai is densely populated compare to other areas and most of buildings in

these areas were constructed in 17th Century. 53% of the buildings are within 20 years of age. 14%

are between 20 to 40 years of age. The bureau of Indian Standard revised Chennai city from Zone II

to Zone III. Since 77% of the buildings were constructed before the year 2002 and this building can‘t

meet seismic design code for Zone III for the city. Even though these areas are moderate seismic

hazard, due to dense population and old buildings nature, the vulnerability is very high compared to

other areas. The probability of damage to these structures can be depending on their impact on the

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earthquake strength of the building by simple Rapid Visual Screening Techniques (Ravi Sinha and

Alok Goyal, 2001).

The critical facilities like hospitals and educational institutions are situated in densely populated

areas falls under moderate seismic hazard and these areas are more vulnerable in terms of population

density. However the city doesn‘t have much high potential loss facilities like dams, levees, military

installations, nuclear power plants and hazardous material sites within the city limit. The length of

roads in the city viz, cements concrete, bituminous and Water bound macadam are 83kms, 3,656kms,

and 11kms respectively. Since the sewage system designed before the 2002, it should be checked

thoroughly for leakage coz, earthquake is related to ground shaking phenomenon and the sewerage

system of Chennai covers 99% of city‘s total area, it would be highly vulnerable during earthquakes.

About 195 parks with extent varying from 150sq.m to 35,000sq.m and totalling to more than

6,00,000sq.m. Playgrounds maintained by Chennai Municipal Corporation is concerned, is more than

200 nos., with a total extent exceeding 5,00,000sq.m. These areas should avoid for future

development and can be used for emergency shelters.

6. Conclusions

Seismic risk macro-zoning is useful principally for regional policy-making and planning purposes.

Seismic risk micro-zoning is likely to emerge as an important land-use planning tool for local

planning and development in areas of high seismic risk (UNDRO-3, 1978). Since the present seismic

hazard map for Chennai is GIS based one it can be used as first level regional studies. Further the

map can be refined with more geophysical and geotechnical informations for future detailed site

specific studies. Vulnerability analysis in disaster prone areas is not only fundamental to formulation

of building codes, as widely accepted, but is even more important for the general process of physical

planning, and land use planning in particular, especially with regard to locational decisions for new

development. The vulnerability of the buildings, critical facilities, lifeline strictures should be

studied thoroughly for further planning purposes. The present vulnerability study is based in spatial

distribution and relative risk based. However the likely damage to structures should be categorised in

different grades depending on their impact on the seismic strength of the building. This kind of

studies will be useful to identify the need for retrofitting. Also thorough study and regular health

check up should be recommended for the vulnerable buildings in the high seismic hazard areas of the

city.

Land use zoning ordinances for disaster prevention may control types of development (residential,

open space, commercial, industrial or other), density of development and type of construction

(UNDRO, 1978). Such as the case the land-use zoning for disaster prevention in earthquake-prone

areas of Chennai requires the designation of zonal significance. The characteristics of each zone, the

basis for land—use controls, zoning ordinances, building codes, and building or location permits

should be clearly demarcate in the city developmental.

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Acknowledgements

The present study is the part of ISRO Ongoing project-ISRO/RES/4/548/09-10. The authors thankful

to SAC, ISRO for funding under RESPOND programme. The authors are grateful to the Officials of

Census of India, Madras Metropolitan Authority (MMDA), Corporation of Chennai, Metro Water,

Central Ground Water Board and Geological Survey of India, Chennai for providing the data and

necessary information without which this work would not have been possible. The first and third

author acknowledges all the facilities provided by Mr. G. Viswanathan, Chancellor, VIT University,

Vellore, India.

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