Central Seismological Observatory, India Meteorological Department, Shillong-793005
The Northeastern region of India has witnessed several devastating earthquakes such as the 1869, 1897, 1950 great earthquakes and some high magnitude earthquakes ranging from 6.0 to 8.7. In the light of scientific earthquake predictions given for the region, urgent measures need to be taken for earthquake disaster risk mitigation, both structural as well as non-structural, in addition to efforts made so far.National disasters policies and programmes are yielding results in generating awarenessand increasing the level of preparedness, which are vital for mitigation of disasters.In this paper some aspects are discussed in specific areas of Capacity Building,Techno-Legal Framework, Techno-Financial Regime., and enforcement of Rules &Regulations to further strengthen the institution of disaster management in carrying out structural and non-structural mitigation measures.
Keywords Earthquake, Northeast India, Meghalaya, Shillong
The Northeastern part of India is one of the most seismically active regions in the world. The North eastern region of India is tectonically very active due to the collision of the Indian plate with the Tibetan landmass in the north and the ongoing subduction process between the Indian plate and the Shan-Tenasserim block in the east. The Shillong plateau and the neighbouring areas being subjected between two mobile belts, are under immense stress which when strained generates a number of earthquakes along the existing faults and thrusts.
This Northeastern region of India has witnessed several devastating earthquakes such as the 1869, 1897, 1950 great earthquakes and some high magnitude earthquakes ranging from 6.0 to 8.7.
The Shillong plateau, a part of the peninsular Indian shield, is bounded between 300 km long east west Dauki fault system to the south, the north-south trending Jamuna and Dhubri faults to the west and northwest-southeast Kopili fault which separates the Shillong plateau from the Mikir hills to the east. Some other major structures such as the northeast-southwest lineament of Tyrsad-Barapani shear zone also traverse the Shillong plateau. A northwest-southeast trending thrust which is about 90–100 km dipping towards the northeast within the plateau is the northwest extension of the Dauki fault named the Dapsi thrust.
Shillong plateau behaves as an independent tectonic entity, with its own style of faulting, seismic productivity and hazard potential.
While renowned scientists and seismologists have been predicting earthquakes of Magnitude 8 or more (with an intensity of IX MSK and above) in the North-Eastern region of India, for quite some time now, urgent measures need to be taken for earthquake disaster risk mitigation, both structural as well as non-structural, in addition to efforts made so far.
The distribution of earthquake events in the northeastern region of India are generally co-related with known Regional Thrusts, The Main Boundary Thrust and The Main Central Thrust. Dr. Harsh K Gupta stated that “Moderate magnitude to great earthquakes in the northeast India region is found to be preceded, generally, by well defined earthquake swarms and quiescence periods.
There is no denying the inevitable. Realistic mitigation measures need to be taken up urgently, for which certain policy decisions are to be made. Presently, there is no scientific technique available anywhere in the world to predict occurrence of earthquakes with reasonable degree of accuracy with regard to space, time and magnitude. It is, therefore suggested that appropriate steps may be taken to ensure that the dwellings and other structures in the region are designed and constructed as per guidelines laid down by the Bureau of Indian Standards(BIS) to minimize the losses caused by earthquakes. The choice of seismic factor to be adopted for designing and engineering the structures depends on the horizontal ground acceleration and various other factors including type of structures, the ground conditions and also importance of structures. For important and critical structure, site specific spectral studies have to be carried out before assessing the seismic design parameters. Suitable seismic design parameters may be adopted as per recommendations of National Committee on Seismic Design Parameters (NCSDP) for designing and engineering Hydroelectric Projects.
Efforts made so far
Great strides have been made in the country towards achieving the goals of Disaster Risk Mitigation. However, the shift in focus towards Risk Management is yet to make its mark.
Some of the achievements are:
• The Disaster Management Act, 2005, has been made effective throughout the country, for institutionalizing disaster management.
• The National Policy came in 2010 with a vision of a safe and disaster resilient India, by developing a holistic, proactive, multi-disaster oriented strategy.
• The National State & District Disaster Management Authorities have been established with wide powers under the D.M. Act, and States have designated Department for Disaster Management.
• Guidelines have been issued by the NDMA covering various kinds of disasters, including one for Management of Earthquakes.
• Building Bye-Laws have been amended so as to ensure earthquake/disaster resistant structures in future.
• National programs for capacity building of Engineers and Architects in earthquake risk management have been completed.
• National Disaster Response Forces (NDRF) have been established in different regions of the country
• National Institute of Disaster Management and Institutes in the States have been established for imparting training in Disaster Risk management (DRM)
• Increasing the level of preparedness of various stakeholders through DRM training programs has been continuing over the past eight or nine years, but is yet to be felt by the community at large
• Disaster Management Plans have been prepared from the State to the District to the Block, down to the village level, but most are response oriented and need updating
• Many schools have prepared School safety Plans, but, again, they are more response oriented
• Master Trainers have been trained in Medical First Responder Course, and training of Master Trainers in Incident Response System(IRS) has been started
• Capacity building of fire and Emergency service and of the Civil Defence & Home Guards is continuing, but both again are for crisis management
The thrusts made so far in Disaster Management are still mostly response oriented as is evident from the creation of the NDRF, adoption of the IRS, conducting mock drills in localities and in schools for any disaster, and even conversion of the Calamity Relief Fund to the Disaster Response Fund.
Mitigation measures such as amending Building Bye-Laws and training of Engineers & Architects or even of Masons in Earthquake Risk Management may lead to safer buildings in future, but special effort needs to be made to address the problem of existing built environment.
Cities have been identified for Seismic Microzonation and in the North-East, work for cities of Guwahati and Gangtok have been completed. However, these studies will again provide some help only for future urban development by identifying hazard prone areas. For existing structures, doubt will still remain about their seismic safety, since response of a building to any seismic wave is site specific. Studies done for Shillong city show that there are wide variations in resonance frequencies even at short distances, which indicate heterogeneity in soil layers. The northeastern region of India has plenty of exposures called “Safety Valves” according to their dynamics for releasing interior energy in a limited time interval which might otherwise form a great earthquake.
Some states have taken up Vulnerability and Risk Assessment for the different Hazards, but can an acceptable of risk be defined, especially I view of the policy of Zero Tolerance? However, such Risk Assessments are essential for any meaningful mitigation strategy to be drawn up, but the methodology must be standardized and codified.
Hazards and Disasters:
The international Secretariat for Disaster Reduction (ISDR) defines a hazard as “a potentially damaging physical event, phenomenon or human activity that may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation.” Hazards could be, natural (geological, hydro-meteorological and biological) or induced by human processes (environmental degradation and technological hazards). Hazards can be single, sequential or combined in their origin and effects. Accordingly, Hazard analysis entails the identification, study and monitoring of a hazard to determine its potential, origin and characteristics.
A fine line separates environmental hazards and environmental resources, as between water out of control (flood hazard) and water under control (reservoir resources).
Classification of Hazards
Though hazards could be classified on many criteria; some of the general classifications described by S. Gopalakrishnan are as follows:
• Sudden onset hazards: geological and climatic hazards such as earthquakes, tsunamis, floods, tropical storms, volcanic eruption and landslides.
• Slow onset hazards: (environmental hazards) drought, famine, environmental degradation, desertification, deforestation and pest infestation.
• Industrial/Technological: system failures/accidents, spillages, explosions, and fires.
• Wars and civil strife: armed aggression, insurgency, terrorism, and other actions leading to displaced persons and refugees.
• Epidemics: water and/or food-born diseases, personto-person diseases (contact and respiratoryspread), vector-born diseases and complications from wounds.
Hazards could also be classified as direct and indirect. For example, earthquake hazard would lead to direct and indirect consequences, tabulated as under(ibid):
• Ground shaking
• Differential ground settlement
• Soil liquefaction
• Immediate landslides or mud slides, ground lurching and avalanches.
• Permanent ground displacement along faults
• Floods from tidal waves, sea surges & tsunamis
• Dam failures
• Pollution from damage to industrial plants
• Delayed landslides Site risks in an earthquake prone area, as explained by S. Gopalakrishnan, would be:
• Slope risks: slope instability, triggered by strong shaking may cause landslides. Rocks or boulders can roll considerable distances.
• Natural Dams: landslides in irregular topographic areas may create natural dams, which may collapse when they are filled. This can lead to potentially catastrophic avalanches after strong seismic shaking.
• Volcanic Activity: earthquakes may be associated with potential volcanic activity and may occasionally be considered as precursory phenomena. Ash falls and/ or pyroclastic flows, volcanic lava or mudflows, and volcanic gases normally follow explosive eruptions.
Besides, hazards can be of both short-term and long-term duration as per the classification proposed by K. Smith.
Risk is precisely defined by the ISDR as “the probability of harmful consequences, or expected losses (deaths, injuries, property, livelihoods, economic activity disrupted or environment damaged) resulting from interactions between natural or human induced hazards and vulnerable conditions”. Conventionally, the notation expresses risk:
Risk = Hazard x Vulnerability. Some disciplines also include the concept of exposure to refer particularly to the physical aspects of vulnerability.
Disaster risk is seen as a function of the hazard, exposure and vulnerability, denoted by the mathematical function:
Disaster Risk= function (hazard, exposure, vulnerability) where “exposure” refers to the element which is affected by natural disasters, people and/or property. Risk perception is understood as the ‘awareness’ of risk, which differs in different cultures/societies.
Seismic Hazard and Risk Mitigation
Microzonation is the process of dividing a geographic domain into small units of likely uniform hazard level and nature. This classification is done based on Geoscientific, Geotechnical, Seismological and engineering seismological parameters. The hazard micro zone map is transformed
into seismic risk microzonation map with inputs on vulnerability of built environment and Anthropological /Socialogical inputs. As earthquake prediction is not possible precisely in time and space, seismic Hazard microzonation provides an important tool for generating parameters for site specific structural designing, land use planning and disaster mitigation. Seismic microzonation studies have been completed for Delhi (1:50,000 scale), Guwahati (1:25,000 scale), Sikkim (1:25,000 scale) and Bangalore city (1:25,000 scale). Microzonation map for NCT of Delhi is further being refined at 1:10,000 scale.
Loss of lives during an earthquake is mostly due to damage or collapse of houses/structures. However, a structure can bear the vibration from an earthquake if it has enough strength and sturdiness. Bureau of Indian Standards (BIS) has published criterion for construction of earthquake resistant structures. The design of a structure should be such that the whole structure behaves as one unit at the time of vibration rather than like an assemblage of parts. Important structures like hospitals, fire stations, etc, should be made earthquake resistant to the highest probable intensity. In the existing environment, it is not economical to demolish and reconstruct most of the poorly built structures; for such poorly built structures, guidelines for their assessment and retrofitting have been prepared by the National Disaster Management Division in the Ministry of Home Affairs, under the Gol-UNDP Disaster Risk Management Programme. Guidelines for assessment and retrofitting of R.C.C are under preparation by the BIS. In addition to this, HUDCO & BMPTC have published also guidelines and brochures for construction and retrofitting of buildings.
Efforts are being made to improve the understanding of earthquake processes and their impact towards better management and mitigation of the effects of earthquakes in future.
Furthermore, losses due to earthquakes can be considerably reduced through proper planning and implementation of pre and post disaster preparedness and management strategies by respective state government agencies by working out the possible earthquake effects for various seismic zones.
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