An earthquake is a phenomenon that occurs without warning and involves violent shaking of the ground and everything over it. It results from the release of accumulated stress of the moving lithospheric or crustal plates. The earth’s crust is divided into seven major plates, some 50 miles thick, which move slowly and continuously over the earth’s interior and several minor plates.
Earthquakes are tectonic in origin; that is the moving plates are responsible of the occurrence of the violent shaking. The occurrence of an earthquake in a populated area may cause numerous casualties and injuries and extensive property damage.
Earthquake Risk in India
India today has an increasing population and extensive unscientific constructions mushrooming all over, including multistoried luxury apartments, huge factory buildings, gigantic malls, supermarkets and warehouses and masonry buildings. India is thus at high risk. During the last 15 years, the country has experienced 10 major earthquakes that have resulted in over 20,000 deaths. As per the current seismic zone map of the country (IS 1893: 2002), over 59 per cent of India’s land area is under threat of moderate to severe seismic hazard, i.e., prone to shaking of MSK Intensity VII and above (BMTPC, 2006). In fact, the entire Himalayan belt is considered prone to great earthquakes of magnitude exceeding 8.0, and in a relatively short span of about 50 years, four such earthquakes have occurred: 1897 Shillong (M8.7), 1905 Kangra (M8.0), 1934 Bihar-Nepal (M8.3), and 1950 Assam-Tibet (M8.6). Scientific publications have warned of the likelihood of the occurrence of very severe earthquakes in the Himalayan region, which could adversely affect the lives of several million people in India.
The regions of the country away from the Himalayas and other inter-plate boundaries were considered to be relatively safe from damaging earthquakes. However, in the recent past, even these areas have experienced devastating earthquakes, albeit of lower magnitude than the Himalayan earthquakes. The Koyna earthquake in 1967 led to the revision of the seismic zoning map resulting in the deletion of thenon-seismic zone from the map. The areas surrounding Koyna were also re-designated to Seismic Zone IV, indicating high hazard. The occurrence of the Killari earthquake in 1993 resulted in further revision of the seismic zoning map in which the low hazard zone or Seismic Zone I was merged with Seismic Zone II, and some parts of Deccan and Peninsular India were brought under Seismic Zone III consisting of areas designated as moderate hazard zone areas. Recent research suggests that as the understanding of seismic hazard of these regions increases, more areas assigned as low hazard may be re-designated to higher level of seismic hazard, or vice-versa.
The North-Eastern part of the country continues to experience moderate to large earthquakes at frequent intervals including the two great earthquakes mentioned above. Since 1950, the region has experienced several moderate earthquakes. On an average, the region experiences an earthquake with magnitude greater than 6.0 every year. The Andaman and Nicobar Islands are also situated on an inter-plate boundary and frequently experience damaging earthquakes.
The increase in earthquake risk is also caused due to a spurt in developmental activities driven by urbanization, economic development and the globalization of India’s economy. The increase in the use of high-technology equipment and tools in manufacturing and service industries have also made them susceptible to disruption due to relatively moderate ground shaking. As a result, the loss of human life is not the only determinant of earthquake risk any more. Severe economic losses leading to the collapse of the local or regional economy after an earthquake may have long-term adverse consequences for the entire country. This effect would be further magnified if an earthquake affects a mega-city, such as Delhi or Mumbai.
Even though the country has experienced devastating earthquakes at regular intervals, these experiences have not been fully used to initiate activities to mitigate the damaging effects of future earthquake disasters. In 1993, a major earthquake occurred near Killari in Maharashtra resulting in the death of over 7,900 people. Following the earthquake, the Government of Maharashtra undertook several risk management and risk reduction activities. These included development of disaster management plans for each district. However, in 2001, the neighbouring state of Gujarat experienced a major earthquake killing over 13,800 people. Unfortunately, earthquake disaster management initiatives were not undertaken in Gujarat before this earthquake even though the seismic hazard of Gujarat is much higher than that of Maharashtra, with a large area falling under Seismic Zone V or the highest risk zone. Following the 2001 earthquake, Gujarat has undertaken a large number of disaster management activities, but these are not being replicated in other high-risk states.Earthquakes of magnitude 6.0 or larger on the Richter scale usually result in a large number of casualties. Ninety per cent of casualties result directly from the collapse of buildings. Secondary events, such as landslides, floods, fires, and tsunamis, account for the remainder (10 per cent) of the casualties. Most of the seriously wounded casualties are trapped under rubble. Both assessment and treatment are severely constrained by the confined surroundings in which the casualties are found. In all those extricated from under the rubble, crush injuries are most common. Death and injury rates are considerably higher among those trapped as compared to the rest of the casualties. Mortality increases with age, disability and degree of destruction of the structure in which the person was trapped. Mortality also is related to the duration of entrapment. The ratio between the incidences of death to injury varies between the different earthquakes, but an average of one death has been observed for every three persons injured. The leading causes of injury are impact and crush by moving debris. The most common injuries are crush injuries, spinal injuries, head injuries, fractures, lacerations, contusions and abrasions. These account for more than 75 per cent of the total number of injuries encountered by healthcare professionals. Less than 10 per cent cases require major surgery. In survivors, trauma to the extremities is the most common injury, especially the lower extremities. A significant proportion of mortality and morbidity could be prevented by the implementation of early and appropriate medical response at the disaster site. Many deaths can be prevented by early implementation of medical and surgical interventions such as proper airway control, limitation of blood loss, treatment of crush injury, and treatment of shock. Common causes of preventable deaths include crush injury, haemopneumothorax, and slow exsanguinations. Even patients with minor injuries need to be clinically observed. Medical personnel should be aware of the unique problems that earthquake casualties present. The current level of medical preparedness is low in the country. A robust preparedness and training system needs to be developed in the healthcare facilities across the country, particularly those located in seismic zones III, IV and V.
The level of awareness of earthquake risk prevalent in the country and the systemic strategy to face damaging earthquakes are rather low. The earthquake risk can be reduced only if there is better and more widespread understanding of the contributors to the risk, and requires concerted efforts by all the stakeholders.
What to Do during an Earthquake?
Stay as safe as possible during an earthquake. Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimize your movements to a few steps to a nearby safe place and stay indoors until the shaking has stopped and you are sure exiting is safe.
If indoors
• DROP to the ground; take COVER by getting under a sturdy table or other piece of furniture; andHOLD ON until the shaking stops. If there isn’t a table or desk near you, cover your face and head with your arms and crouch in an inside corner of the building.
• Protect yourself by staying under the lintel of an inner door, in the corner of a room, under a table or even under a bed.
• Stay away from glass, windows, outside doors and walls, and anything that could fall, such as lighting fixtures or furniture.
• Stay in bed if you are there when the earthquake strikes. Hold on and protect your head with a pillow, unless you are under a heavy light fixture that could fall. In that case, move to the nearest safe place.
• Use a doorway for shelter only if it is in close proximity to you and if you know it is a strongly supported, loadbearing doorway.
• Stay inside until the shaking stops and it is safe to go outside. Research has shown that most injuries occur when people inside buildings attempt to move to a different location inside the building or try to leave.
• Be aware that the electricity may go out or the sprinkler systems or fire alarms may turn on.