Earthquakes hazards may be divided into three sub-categories:
(a) Biological Hazards:
It causes sudden increase or decrease of population of species in a given habitat either due to increased nutrients or increase of toxic chemical elements.
(b) Physical Hazards:
Which causes forest depletion, Landslides and accelerated soil erosion.
(c) Chemical and Nuclear Hazards:
It includes release of toxic chemical elements in the air, water and soil, sudden outburst of lethal poisonous gases from chemical factories, nuclear explosions and leakages of radioactive elements from nuclear reactor plants.
An earthquake is a major demonstration of the power of the tectonic forces caused by end genetic thermal conditions of the interior of the earth. It is a motion of the ground surface, ranging from a faint tremor to a wild motion capable of shaking buildings causing gaping fissures to open in the ground. The earthquake is a form of energy of wave motion transmitted through the surface layer of the earth in widening circles from a point of sudden energy releases called the ‘focus’.
The place of origin of earthquake is focus, which is always hidden inside the earth, the depth of which varies from place to place. The deepest earthquake may have its focus at a depth of even 700 km below the ground surface but some of the major Himalayan earthquakes have their focus around 20-30 km deep. The place on the ground surface, which is perpendicular to the buried ‘focus’ or ‘hypocenter’ recording the seismic waves for the first time is called ‘epicenter’. These seismic waves are recorded with the help of an instrument called ‘seismograph’ or ‘seismometer’ at the epicenter.
Seismologists cannot directly observe rupture in the earth’s interior, they rely on seismograms, geodetic measurements and numerical modeling to analyze seismic waves and accurately assess the size and other physical characteristics of earthquakes.
The Richter scale is a famous example of such a scale. However, the Richter scale is not well suited to accurately measure earthquakes with magnitudes over approximately 6.8, and was furthermore originally defined by Charles Richter to apply to earthquakes only in Southern California. The Richter scale invented by Charles F. Richter in 1935 measures the magnitude or intensity of energy released by an earthquake.
Another Scale of the measurement of the intensity of an earthquake depends on a variety of factors, e.g., magnitude, distance from epicenter, acceleration duration, amplitude of waves, type of ground water table, nature of geometrical of the region concerned and the nature and type of constructions affected by an earthquake.