Earthquake is the shaking of the ground due to the vibration caused by internal energy release. It occurs for very short time. The sudden release of energy causes the seismic waves that make the ground shake. When two block or two plates are rubbing against each other, they stick a little then create the seismic waves and that can be felt as ground shaking. At the earth’s surface, earth quakes manifest themselves by shaking and displacing or rupturing the ground. When the epicenter of a large earth quake is located offshore, the seabed may be displaced sufficiently to causes a tsunami. Earth quakes can also trigger landslide and occasionally volcanic activities.
Earthquake is a violent tremor in the earth crust, sending out a series of shock and aftershock waves (L waves) in all direction from its focus. Earthquakes constitute one of the most terrible natural hazards which often turn into disaster causing extensive devastation and loss of human lives and their properties.
Causes Of Earthquake
Earthquake of Nepal and India along the Himalayan belt were caused mainly due to collision of Indian plate and Eurasian plate. Deep focus and high magnitudes of earthquakes are caused along the convergent plate boundaries because of collision of two convergent plates, namely Eurasian and Indian convergent plates. The subduction of Indian plate below Eurasian plate caused Nepal earthquake at the belt of Himalaya. April 25 and May 12, 2015 earthquakes had occurred on the northern boundary of the Indian plate which is under thrusting the Eurasian plate. The main cause of Nepal earthquakes is attributed to the northward movement of Indian plate. The Indian plate is moving toward north- northeast ward direction at an average rate of about 4.5-5 cm per annum, which causes a stress. On 25th April 2015, the stress built up as the Indian and Eurasian plates slide under one other causing earthquake. The epicentre of these two earthquakes has lay on the boundary of these two plates. The earth quake was caused at the depth of 10 kilometres. The 188 aftershocks measuring around 3.0-6.9 magnitudes in Richter scale were at the depths of 10-50 kilometres. After the major earthquake, the earth’s plates lost their equilibrium.
Consequences Of Earthquakes
The hazardous effect of Nepal earthquakes depends not only on their magnitude of Richter scale or intensity alone, but also on so many factors, such as geology of the earth crust (lithology, elasticity, soil condition, permissible stress, rock structure, etc.), design of buildings, quality of construction, population pressure, etc. Several villages, towns, human constructions and their properties, lives were completely damaged. The urban area of Kathmandu, the capital of Nepal, was completely destroyed by April earthquake which hit Nepal. Several buildings collapsed like a pack of cards as if they were mud huts.
The April 2015 Nepal earthquake (also known the Gorkha earthquake) killed nearly 9,000 people and injured nearly 22,000. It occurred at 11:56 Nepal Standard Time on 25 April, with a magnitude 7.8Mw or 8.1Ms. Its epicenter was east of Gorkha District at Barpak, Gorkha and its hypocenter was at a depth of approximately 8.2 km (5.1mi). It was the worst natural disaster to strike Nepal. The earthquake triggered an avalanche on Mount Everest, killing 21, making 25 April 2015 the deadliest day on the mountain in history. The earthquake triggered another huge avalanche in the Langtang valley, where 250 people were reported missing.
Centuries old buildings were destroyed at UNESCO World Heritage Sites in Kathmantu Valley, including some of the Kathmandu Durbar Square, the Patan Durbar Square , the Bhaktapur Durbar Square, the Changu Narayan temple, the Baudhanath stupa and Swayambhunath stupa. Geophysicists and other experts had warned for decades that Nepal was vulnerable to a deadly earthquake, particularly because of its geology, urbanization, and architecture.
Some Safety Measures of Earthquake:-
Earth quick is generally unpredictable in the countries like Nepal where technology is not well developed, therefore it can’t be said where and when does the disaster occur and cause fetal damage to the human being, property and even the nature. However there are some safety measures to minimize the loss and damage of human life and physical developments.
Some safety measures can be listed as below:-
1. Protect yourselves from the Earthquake when you hear some Earthquake warnings and pre symptoms because huge earthquakes has pre shocks before it’s actual arrival.
2. Generally Earthquake causes falling of heavy materials kept on upper parts of your rooms therefore to be safe from those falling objects you need to stay under the large table until a quake is gone.
3. Stay away from book-cases and other furnitures that can fall on you.
4. If you are inside the kitchen then turn off the switches of gas and electricity so that there may not occur fire catch and let the door opened so that you can escape if any danger inside the room.
5. If you are in bed then hold on and stay there, protect the head with a pillow to protect yourselves from falling glass and other debris.
6. House is the most safety and important place at any time therefore the safety measures should be taken while constructing your house. The Earthquake proof house is necessary to build and the house should have equipped with fire extinguisher, first aid kit, emergency food storages, lighting facilities and exit ways at needed.
An earthquake cannot be prevented or accurately predicted, but there are some forewarning sign of a coming tremor, and there are various system being developed and in use to reduce the damage from this disaster. However, no perfect techniques have been developed to predict the tremor till date. Making exact prediction about the occurrence of a tremor in an area and time is still a tricky proposition. The seismologists are more and more concentrating on the aspect of earthquake forecasting. When we would be able to predict of earthquakes accurately on the basis of animal behavior or other unusual phenomena, it would save many lives and property damages.
[Writer:- Shanta Chaudhary (Masters in Environmental Science in Tribhuvan University), she is the first Tharu girl to participate in ‘World Water Forum 2006’ in Mexico, America)]