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Evaluation of earthquake damage in Delhi

A slide presentation for Disaster Management
Delhi is one of the maga-cities of the world with population of 10 million and has been projected to become the second largest city in India by the year 2025. Both politically and economically, Delhi is one of the most important cities in our country and its ability to with stand disasters is of critical importance to the entire country. Delhi faces severe earthquake hazard due to its vicinity to the tectionically active Himalayan region. In addition, several small faults exist very close to the city and their activity may lead to strong ground motions in Delhi. It is essential that a comprehensive earthquake disaster management plan is prepared and implemented in Delhi. Experience of other major cities that have implemented effective disaster management plan shows that the plan should include the following elements : (1) hazard (2) vulnerability, (3) exposure of people, and (4) economic impact Inclusion of all these elements enable cost-benefit evaluation of different short-term and long-term options for risk reduction and disaster management.

In the past, all these elements were not considered in the disaster management plans of developing countries due to paucity of data.

Case study of Mumbai
Recent experience in Mumbai shows that the existing information from the city authorities and census data can be combined with vulnerability estimates and morbidity statistics to estimate the extent of damage and human loss due to earthquakes of a particular intensity. The results of such studies are in terms of numbers of houses damaged/collapsed and the number of people killed and injured.

This information can be used to develop disaster management plan to tackle post-earthquake scenario and to plan steps to decrease the consequences through suitable structural and non-structural measures. The loss estimates for Mumbai are presented as an example to demonstrate their use in disaster management.-

Urban India
India has experienced explosive urbanization over the last few decades.

  • 23 cities have over 1 million population (1991)
  • 276 cities have over 0.1 million population (1991)

Urban growth is largely unplanned

  • Unauthorised densely populated colonies
  • Lack basic amenities
  • Relatively low standard of living

Urban society may lack resilience to with stand disruptive force.

Delhi profile

  • City population exceeds 14 million.
  • Around 60% population lives in informal housing and slums.
  • Building codes/standards have been poorly implemented
  • Many building and other structure are very old and weak.

  

Administrative set-up

  • Delhi is the capital of India as well as a State in itself.
  • Both national and state governments are based in Delhi
  • Different agencies are controlled by State or National governments/administrators.
  • Lt.Governor and Chief Minister are the highest authorities.

Disasters management strategies must consider interaction between different agencies.

Risk management

  • Disaster management plan should consider the following factors;
  • Hazard
  • Vulnerability
  • Exposure
  • External context (Economic impact)
  • Earthquake risk of Delhi is the intersection of all these factors.

Disaster management should consider cost benefit of different options for risk reduction.

Seismic hazard

  • Seismological studies
  • Geological studies
  • Historical data

Objective – probability of earthquake exceeding a particular intensity in a given number of years.

Current status – maximum level of earthquake acceleration that is likely during the life of the structure (IS: 1893-1994)

Site effects

  • Effect of soil condition and topology is typically reflected through seismic microzonation maps.
  • Areas of city with likelihood of local amplification of seismic waves are identified.
  • Soft soils and hilly terrains both lead to amplification of seismic waves.

Structures in these areas need to be designed for higher seismic forces.

Structural vulnerability

  • Estimation of likely level of damage to buildings due to postulated earthquake.
  • Estimation of likely economic loss due to postulated earthquakes.
  • Estimation of casualty levels.

Information from vulnerability evaluation is very useful for planning relief and recovery measures after an earthquake.

Seismic vulnerability

  • Depends on type of structures (structure category) and their age.
  • Depends on land use in city (space between adjacent buildings, height of buildings etc.)
  • Depends on month and time (buildings may be weaker during the rainly season, and residential building more fully occupied during nights).
  • Depends on population density (impact of damage of a building to number of people)

Example of Mumbai
2.76 million buildings (1991)
Engineered constructions

  • 9.08% reinforced concrete buildings
  • 31.35% brick masonry buildings with RCC roof Non -engineered constructions
  • 31.49% informal masonry buildings.
  • 28.08% other non-engineered buildings using light weight materials.

Vulnerability

  • Influence of old constructions on vulnerability needs to be considered.
  • Recent studies show significant deficiency in design and/or construction practice even fir engineered constructions.

Vulnerability index for different construction types is established based on observed behaviour of similar constructions in past earthquakes.

Seismic vulnerability Index

  MSK MSK VI MSK VII MSK VIII
Reinforced concrete
building
0.00 0.05 0.25 0.50
Engineered masonry
Building
0.05 0.25 0.50 0.75
Non-engineered
masonry building
0.05 0.25 0.50 0.75
Non-engineered
constructions using
other materials
0.10 0.50 0.75 0.95

Casualty model
Consistent morbidity model based on conditional probability can be used to determine casualty levels.

Ksb = D5b x [ M1b x M2b x M3b x M4b]

B is building type
Ks is estimated number of people killed in b
D5 is total number of damaged buildings
M1 is number of occupants per building
M2 is probability of occupation of building
M3 is probability of occupants getting injured

Building damage

  MSK V MSK IV MSK VII MSK VIII
Reinforced concrete
building
0 12,600 62,000 125,700
Engineered masonry
building
43,400 217,000 434,000 651,100
Non-engineered
masonry building
38,900 194,400 388,800 583,200
Non-engineered
constructions using
other materials
87,200 435,900 653,900 828,200
Casualty
Time MSK VI MSK VII MSK VIII
Midnight 31,400 118,400 277,600
6 A.M 25,000 94,600 22,100
12 Noon 18,800 71,000 166,500
Death estimate
Time MSKVI MSK VII MSK VIII
Midnight 11,200 42,600 100,100
6 A.M 9,000 34,000 80,000
12 Noon 6,700 25,500 60,100

Structural mitigation measures

Engineered constructions

  • Better compliance with design codes
  • Careful detailing.
  • Good quality control
  • Leads to reduction in vulnerability

Non-engineered constructions.

  • Difficult to implement any mitigation measures
  • No reduction in vulnerability

Reduced vulnerability Index

  MSK V MSK VI MSK VII MSK VIII
Reinforced Concrete
building
0.00 0.03 0.15 0.30
Engineered masonry
building
0.00 0.05 0.25 0.50
Non-engineered
masonry building
0.00 0.05 0.25 0.50
Non-engineered
constructions using
other materials
0.10 0.50 0.75 0.95

Injury estimate for 2011
Mitigation

Time Yes No Yes No Yes No
  MSK VI   MSK VII   MSK VII  
Midnight 36,500 40,800 139,700 153,900 333,600 361,000
6 A.M 29,200 32,600 111,800 123,100 266,900 288,700
12 Noon 21,900 24,500 83,800 92,300 200,2000 216,500

Death estimate for 2001
Mitigation

Time Yes No Yes No Yes No
  MSK VI   MSK VII   MSK VIII  
Midnight 13,200 14,700 50,700 55,500 121,00 130,400
6 A.M 10,600 11,700 40,600 44,300 96,900 104,300
12 Noon 7,900 8,800 30,400 33,300 72,700 78,200

Conclusions

  • Seiismic vulnerability can be decreased by proper choice of construction technioque. Good engineered constructions are essential.

Structural mitigation measures tend to reduce earthquake risks only in the long-term. They must be used in conjunction with other measures.

  • Vulnerability analysis results can provide invaluable assistance in relief and recovery following an earthquake disaster.
  • Engineering community needs to play a pro-active role to reduce vulnerability of urban areas.