Damage due to earthquakes depends on various factors listed below:
Nature of Earthquakes:
It includes various parameters like magnitude, intensity, and duration and ground acceleration due to earthquake. Higher the value of these parameters, higher will be the resultant damage.
Geological and Soil Conditions:
Geology and Soil conditions play a very important role in the amount of damage due to any earthquake. In hilly areas, damages are severe due to various aftereffects of earthquakes such as landslides, blockage of connecting roads, diversion of river flows and damage to dams. The intensity of earthquake is directly related to the type of supporting soil layers. The structures built on the solid rock and firm soil generally perform better. There are cases in which the intense vibrations from the earthquake “liquefied” the soil and buildings tilted on to the ground because the foundation became loose.
Quality of Construction:
Construction quality is very important for safety of buildings. Building designs must be such as to ensure that the building has the adequate strength, and will remain as one unit while subjected to vibrations and significant deformation; otherwise, it will suffer great damage. The great loss-of life and property due to poor construction practices can be seen in major earthquakes.
Various sociological factors such as density of population, time of occurrences, community preparedness are very important for limiting the resultant damage.
The nature of the damage that can occur as a result of any earthquake may well be imagined. Everything based upon the stability of the earth is rudely disturbed. If the tilt or displacement of the ground disrupts the equilibrium, structures fall. Gravity spares nobody.
Therefore, the maximum damage is noticed in the case of tall buildings. If these are not designed to withstand any substantial ground movement, they will fall. Tall buildings and roofs are the first casualties. In the wake of their collapse, most damage to life is done to those who are inside the house. Many will be hit by falling debris or are trapped inside the collapsed building. Persons trapped under the debris, shouting pathetically for help, constitute a truly gruesome sight. Sometimes steel beams have to be cut before the victims can be rescued.
Essential services such as water – mains, drainage systems, and electrical transmission lines are seriously damaged. Broken water – mains cause flooding of the area and leave no water for drinking or for fire fighting. The sparking of high-tension overhead electric cables cause fires, setting ablaze whatever combustible material is in the vicinity. Leaks from cooking gas cylinders or supply lines also cause fires.
Disrupted drainage lines spread noxious fluids and give rise to diseases and epidemics.
Geological faults in the Earth’s crust become activated and accentuate displacement of the ground, producing gaping fissures in which human beings and animals are known to have been engulfed. Telephone and telegraph poles fall down and the services go out of order. Communications are seriously hampered or altogether stopped. Railway lines are twisted out of shape and rail communication to and from the affected area is broken off. In some cases, the only access to the affected area is by helicopter.
Large dams in the vicinity may be affected, and in some cases may even burst and cause severe floods. On the coast, huge waves called tsunamis lash the shore, bring down houses and other structures, and dislocate ‘fishing and navigation.
Creation of new islands is a rare phenomenon but does occur due to some earthquakes, which originate below the seabed. The new islands were composed of loose sand and clay mostly and are eroded due to sea waves and tides.