Nepal lies in the central part of the Himalayan belt. Because of its location characterized by a rugged topography, very high relief, variable climate conditions, complex geological structures with active tectonic processes and continued seismic activities, Nepal is prone to natural disasters. Obviously, the country requires a strong coping strategy and DRM to minimize the negative effects of natural disasters. But various human interventions have hastened the occurrences of natural disasters. Due to this, the vulnerable groups, mainly the poor and the marginalized people from the rural and urban areas, are facing economic hardships and bearing all kinds of burden. Insufficient knowledge on DM, emerging climate risks, low literacy rates, inadequate physical infrastructure, poor forecasting facilities and unplanned settlements have worsened the situation. Frequent problems related with the livelihoods have hit the vulnerable people the most. Agriculture is the hardest hit sec....Show More
Nepal lies in the central part of the Himalayan belt. Because of its location characterized by a rugged topography, very high relief, variable climate conditions, complex geological structures with active tectonic processes and continued seismic activities, Nepal is prone to natural disasters. Obviously, the country requires a strong coping strategy and DRM to minimize the negative effects of natural disasters. But various human interventions have hastened the occurrences of natural disasters. Due to this, the vulnerable groups, mainly the poor and the marginalized people from the rural and urban areas, are facing economic hardships and bearing all kinds of burden. Insufficient knowledge on DM, emerging climate risks, low literacy rates, inadequate physical infrastructure, poor forecasting facilities and unplanned settlements have worsened the situation. Frequent problems related with the livelihoods have hit the vulnerable people the most. Agriculture is the hardest hit sector.
Nepal is one of the 20 most disaster-prone countries in the world. The data on human mortality for the period 1971-2007 show more than 27,000 deaths, 50,000 injuries, 3,000 missing and approximately 5 million affected people. More people are killed by disasters in Nepal than in any other country in South Asia.One of such disasters is an earthquake.
Earthquake is a physical phenomenon caused by the release of seismic waves from the interior of the earth on its surface. The earthquake produces the seismic waves, which are detected by a sensitive instrument called seismograph, by means of seismometer.
Earthquake is caused by faulting and folding in the crust due to tectonic activities.The mechanism of earthquake is well defined by the Elastic Rebound Theory.The earth is a dynamic body,the plates on the earth are moving continuously,due to which the rocks, at the plate boundaries, are continuously undergoing deformation. During the process of deformation of a plate, a great amount of stress is gradually exerted on the rock. When the stress exceeds the elastic limit, a fracture is developed.But the friction along the fracture resist the movement for a certain time, when the stress exceeds the frictional resistance also, the block moves along a fault plane i.e, an accumulated energy is suddenly released and it travels through the earth shaking the earth's crust for a period of time.This concept of earthquake is called 'Elastic Rebound Theory'.
The earthquake may also occur due to collapse of subterrain cavities and underground mines. The ground may shake due to large scale blasting and the use of heavy machines as well as passing trains and tanks.Big landslides and avalanches are also responsible for ground tremor. Other reason may be the volcanic eruption and collapse of volcanic terrain.
Some of the effects of earthquake can be listed below:
Destruction of Various civil engineering structures like dams, bridges, tunnels etc.
Creation of irregularities and cracks on earth's surface.
Causes of landslides along hill slopes
Changes in courses of river due to faulting across them.
Formation/deformation of lakes, springs, and waterfalls.
Submarine earthquakes may cause Tsunamis.
Subsidence of land mass.
Cracking of gas and water pipes.
Soil liquefaction.
Heavy loss of life and property.
Seismic areas are places which experience earthquakes frequently. The civil engineers must think of making his construction immune to earthquakes. The difficulties in achieving these objectives are:
the exact place of earthquake (this is important because the epicenter region will be worst affected and hence needs maximum protection).
the magnitude of an earthquake (this is important because the cost of construction increases with increases in safety required).
the duration of earthquake (this is important because the extent of the damage will be more if duration is more).
the direction of movement of the ground at the time of earthquake.
The above mentioned factors are crucial because unless they are known, assessment of probable damage due to earthquake to civil engineering structures is not possible.
Some of the civil engineering considerations in seismic areas are:
In seismic areas, the civil engineering Structures like buildings, bridges, dams,etc should be made resistant to earthquake damage.
structures should be designed in such a way that there will be no damage in a minor quake, and avoidance of serious damage or collapse in a major shake.
Seismic risk should be limited to socio-economically accepted levels.
Design, construction and maintenance is done taking in consideration of the possible seismic loads. The structures do not necessarily have to be extremely strong or expensive but have to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.
The epicenter region, probable magnitude and duration of earthquake, direction of movement of the ground at the time of the earthquake are not possible to predict. This brings difficulty in achieving the objective. Proper assessment is necessary to incorporate the required safety factor in producing earthquake-resistant designs .
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