Short essay on the harmful Effects of earthquakes

Instrumental to moderate earthquakes in the Mercalli scale do not have much effect. Typical effects of destructive earthquakes can be of the following types:

(i) Panic:

Vibratory waves accompanying the earthquake cause panic among the animals and humans. More damage is caused by panic.

(ii) Physical damage:

This includes collapse of buildings, cracks in ground, roads, bridges, walls, water tanks, rivers and dams.

(iii) Public health:

This includes danger of diseases on account of pollution of water bodies, breakdown of sewage and sanitary pipes, heart failures and other conditions leading to epidemics.

(iv) Civic services and conveyances:

Civic services like water pipes, sewers, electric connections, roads etc are disrupted. Transmission towers and transformers also collapse.

(v) Disruption of economic activities:

On account of widespread damage and destruction, economic activities of the people like farming, business, tread and services are severely affected. It affects the people to large extent.

(vi) Fire:

Collapse and breakdown of small and big containers containing inflammable substances like gas, petrol, kerosene, chemicals pose the dangers of major fire. Fire is also caused due to short circuit of electric line.

2.9.5. Earthquake belts or Seismic belts: Earthquakes occur in some well defined zones on the earth. These zones are termed as earthquake belts or seismic belts. Most of the earthquakes occur along the circumference of the Pacific Ocean. This is known as Circum-Pacific Belt! Another belt starts from the East Indies, passes through the Himalayas, Asia Minor and goes to the Mediterranean region and the Alps.

This is known as Himalayan – Mediterranean belt. Nearly 68% of the quakes occur in the first belt and 21% in the second belt. Remaining 11% occur in other areas. Rift valley region of East Central Africa is a minor belt. Besides these, earthquakes occur sporadically.

Some Major Earthquakes: Some major recorded worlds over earthquakes are mentioned below:

2.9.7. Forecast of earthquakes: Earthquakes occur suddenly without warning. Their forecast can minimize the destruction. However, till today no completely satisfactory way has emerged to predict the occurrence of earthquake. Some of the observations, which can be correlated with earthquake occurrences, are as follows:

(i) In many instances the earthquakes occur in periodic cycles. However, periodicities in time and space for major earthquakes have not been widely detected or accepted.

(ii) Another approach to the statistical occurrence of earthquakes involves the postulation of trigger forces that initiate the rupture. Such forces have been attributed, for example, to severe weather conditions, volcanic activity, and tidal forces. Usually correlations are made between the physical phenomena assumed to provide the trigger and the repetition of earthquakes.

(iii) For prediction of the time of earthquake occurrence, a proposal is that precursory changes in a region will cause the velocity of seismic waves through the region to change. Thus, if appropriate travel-time residuals are plotted as a function of time, fluctuations will provide a forewarning.

(iv) For many years prediction research has been influenced by the basic argument that strain accumulates in the rock masses in the vicinity of a fault and results in crustal deformation.

Deformations have been measured in the horizontal direction along active faults (by trilateration and triangulation) and in the vertical direction by precise leveling and tilt-meters. Some investigators believe that changes in groundwater level occur prior to earthquakes. It should be noted that water levels in wells respond to a complex array of factors such as rainfall; thus, if changes in water level are to be studied in relation to earthquakes, such factors need to be removed.

(v) Strain buildup in the focal region may have significant effects on other observable properties, including electrical conductivity and gas concentration. Because the electrical conductivity of rocks depends largely on interconnected water channels within the rocks, resistivity may increase before the cracks become saturated. As pore fluid is expelled from the closing cracks, the local water table would rise and concentrations of gases such as radioactive radon would increase.

(vi) Less well-grounded precursory phenomena, particularly earthqu lights and animal behaviour, sometimes draw more public attenli many reports of unusual lights in the sky and abnormal ani behaviour preceding earthquakes are known to seismologists. B these phenomena are usually explained in terms of a release of g prior to earthquakes and electric and acoustic stimuli of vari types. At present there is no definitive experimental evidence support claims that animals sometimes sense the coming of earthquake.