Sudden shaking or trembling of the earth surface is an earthquake. Most earthquake are a minor tremor. Larger earthquakes usually begin with slight tremors but suddenly they turn into violent shocks and after that the intensity of shocks diminishes.
Tremors or shocks are felt for a few seconds only. Earthquake is a hazard that strikes suddenly. Earthquake can occur at any time of the year, day or night. Its impact is very sudden. There are no warning signs of earthquakes. Extensive and sincere research has been conducted but success has eluded humans in the forecast or prediction of earthquake.
Bureau of Indian Standard has prepared a map of India, showing earthquake seismic zones of different intensity. Its revised edition has been published in 2002. India has been divided into four zones. The intensity of each zone, result and losses caused by earthquake are described below:
Zone II - The earthquake is felt by all, some people run outdoor. Heavy furniture may possibly move a little small pieces of plaster fall. Cracks in chimneys.
Zone III - Everyone runs out of doors, slight damage is there even in better designed and strongly built building. More breakage in ordinary bridges houses. Considerable damage to poorly designed and sub-standard buildings bridges, etc.
Zone IV - Slight damage in specially designed and well built building bridges. Heavy damage to poorly designed and badly built structures. Chimneys, poles, memorials, walls fall down.
Zone V - Severe damage to even well built bridges, buildings, foundations are displaced. Cracks and fissures develop in the ground. Practically all structures fall or small are greatly damaged or destroyed.
Delhi and Mumbai are situated in high risk zone IV. The whole of North East India, Kachchh, Gujrat, Uttarakhand, Himachal Pradesh and Jammu & Kashmir are in the very high risk zone V. Now peninsular plateau is not safe from earthquakes. Earthquake of Latur (1993, intensity on rich for scale 6.4) and Koyna (1967 intensity 6.5) in Maharashtra testify it.
(i) Damage of property: when earthquake occurs, all buildings from cottage to palaces and stronger skyscrapers are greatly damaged or totally destroyed. Underground pipelines and railway lines are damaged or broken. Dams on river collapse, resultant floods cause havoc. The earthquake in 1967 in Koyna damaged the Dam.
(ii) Human loss: Duration of tremors of earthquake is normally of only few seconds, but thousands of people may die in this short period. Five severely devastating earthquakes have occurred in India between 1988 and January 26, 2001. Nearly 31000 people lost their lives prematurely.
Bihar earthquake of 1934 and Kangra earthquake of 1905, 10,000 and 20,000 people died respectively. Numerous people lost their shelter and many became orphans. The earthquake that occurred in Gujarat on 26 January, 2001 was devastating and disastrous. More than 25,000 people died due to the impact of this earthquake. The destruction of property was tremendous and could not be estimated properly and exactly.
(iii) Changes in river courses: Sometimes river channels are blocked or their courses are changed due to the impact of earthquake.
(iv) Tsunamis: are caused by earthquake. This is a Japanese word, meaning extremely high sea wave. It wreaks havoc on settlement of coastal areas. It sinks large ships. Tsunami that occurred on 26 December 2004 near coast of Sumatra (Indonesia) property worth billions of rupee. More than two lakh people lost their lives in Southeast Asia, India and Sri Lanka.
(v) Fountains of mud: Due to the intense impact of earthquake hot water and mud appear on the surface and take a form of fountains. In Bihar earthquake of 1934 some cracks and fissures had developed. The fields of farmer were covered by knee-deep mud and the crops were destroyed.
(vi) Cracks and fissures: Sometimes cracks and fissures develop in roads railway tracks, and fields, making them useless. Well known san Andreas fault formed during the earthquake of San Fransisco (California).
(vii) Landslides and avalanches are triggered