Earthquake can be defined as a natural phenomenon in which masses of earth’s crust slip and slide against one another, mostly along a fault line, which creates huge amount of energy which then translates in the form of waves near and below the earth’s surface known as seismic waves. This, in turn, leads to faulting, tremors, liquefaction, landslides, after-shocks or tsunamis. The timing, number and intensity of earthquakes becomes the aggravating factors. The casualty depends on the location of the earthquake leading to collapse of buildings and other structures and more often than not construction practices becomes the deciding factor in the resulting death toll.
Geologists have managed to classify the seismic waves as P and S waves wherein P waves resemble the sound waves, able to travel through both solids and liquids compressing and expanding material as they pass. S waves, are like water waves able only to pass through solids.
As an earthquake triggers, P waves are the first to be initiated followed by S waves which then lead to the surface waves classified as Love and Rayleigh waves wherein both have the potential to move the earth horizontally and Rayleigh being predisposed to create vertical movements, too. Most of the collateral damage which we associate with earthquakes are resultant of these surface waves. Had these waves only moved the ground vertically, the damage might have been under control since most construction can withstand vertical displacement along lines of gravity. But the horizontal waves exert extreme force on standing structures known as G-forces, able to unleash crippling damage. The foundation of a building has a massive role to play with those standing on bedrocks having more ability to withstand pressure than those sitting atop soft or filled in soil leading to liquefaction causing the water below surface to mix with soil causing foundations to turn into mush.
The significantly associated and obvious danger in case of earthquake is the tremors on the ground surface which depending on the intensity that’s measure on a Richter scale has the potential to undermine and cause grave destruction of buildings and damage to properties. Waves run along the surface of the ground making structures lean and topple over and the once the tremors cease the land might settle at a different level causing building to become destabilized. What ensues as a result especially in mountainous regions are landslides, avalanches or mudslides exacerbated by heavy rains and fractured rocky terrains.
The maximum catastrophe caused by earthquakes is experience around fault lines which if hit causes huge damage to constructions which are pulled asunder.
Subsidence or lateral spreading is also a result of earthquakes causing sediments to settle after the vibration stops and mixing with the groundwater which seeps out of fissures leading to flooding of nearby areas.
Manmade barriers to check torrential flow of water are broken, dams weakened leading erstwhile restrained water to follow gravity’s order and submerging lives and properties in its trail of destruction.
Fire eruptions are common in the wake of earthquakes due to topping of burning appliances, tearing of gas lines and disruption of power lines.
Earthquakes along ocean lines lead to tsunami waves which can reach up to 500 kilometers leading to a huge loss of life and property and disaster of unimaginable proportions. Even its milder form, seiches, occurring around lakes can prove deadly for neighbouring locations.
The intensity of earthquake is measured on a Richter scale,quantitative measure of an earthquake's magnitude (size), devised in 1935 by American seismologists Charles F. Richter and Beno Gutenberg and anything above 7.0 on a Richter scale is considered to be fatal. Though scientists and engineers the world over are trying to make more stable constructions able to withstand the wrath of nature, yet it has the power to strike suddenly without any forewarning and leave behind death and desolation. By a better understanding of the risks, we can however take certain steps to minimize or check the casualty rate, and financial implication of this natural disaster.