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Quakes:
causes and prediction
THIS
UNIVERSE Kindly tell me how high
do jets fly.
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Quakes:
causes and prediction
Fracturing of rocks and consequent release of energy by rapid motion, vulcanicity and faulting, initiation of new faults or repeated movement of existing ones are primarily responsible for seismicity. The association of seismic activity with faults was well established by the 1916 California earthquake when the SAF (San Andreas Fault) moved over a linear distance of about 430 km. The Elastic Rebound Theory explaining the origin of earthquakes is solely based on faulting. Percussions or sudden blows from explosions viz. Quarry blasting, bombing, firecracker outbursts, volcanic eruption, vehicular traffic, rockfalls from cliffs and escarpments as well as waterfalls, caverns and mines and rubbing together of two uneven surfaces in landscape, landslides, avalanche and submarine slumping of sediments are other factors associated with earthquakes of mild to moderate intensity.
New scientific studies have testified that "earthquakes lubricate themselves at an early stage and are, therefore, able to spread more rapidly and easily". Dan McKenzic (Cambridge) and James Brune (California) have provided useful information which can help in the prediction of seismic wrath. For instance Koyna earthquake (December 11, 1967) was preceded by a series of tremors for a couple of years before the havoc occurred and going by today’s practice the earthquake could have been predicted and at least 200 lives saved. Prior to the construction of Koyana dam, out of the 78 destructive earthquakes occurring during 200 years, none had visited the vicinity of the Satpura range. Hence, the region was considered to be immune to severe shocks. Collapse of an underground cavern, nuclear test explosion or the isostatic imbalance caused by the impounding of hundred thousand million cubic feet of water etc were held responsible for the Koyana earthquake. Predictions The precise prediction about earthquake calamity is elusive, though it is not impossible, since for human gray matter sky is the limit. Earthquakes occur and recur at some places and new places but not on any regular scale or frequency. The earth scientists know that elastic strain is piling up along the SAF since 1906 but they are unable to forecast the exact day, time and place. In about half of the cases, just before the rocks reach the rupture point to announce the event, small foreshocks announce hours, days or even months before the climax shock, that stress has become critical. The long series of post event tremors indicate adjustments. Sometimes, the break may be as large as the major shock. Unusual animal behaviour, fluctuations of ground water levels in wells and springs and variations in the discharge of springs are the phenomena closely related to the development of fractures. The Chinese are keenly interested in Seismology since 90 per cent of the country rests on the otherwise young and restless crust. "They have successfully employed most of the precursors in predicting major disasters, and have especially mastered the art of closely monitoring and analysing abnormal animal behaviour to forecast earthquakes. The Haicheng earthquake of February 1975 of 7.3 magnitude, ravaged 90 per cent of the structures, but without loss of life due to timely evacuation of the population of nearly a million". There is evidence that full moon and associated high tides, excessive precipitation, sharp barometric gradient changes, and particularly another quake elsewhere act as "triggers" for earthquakes. — The writer is a former Head of the Geography Department, Panjab University
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Tackling cancer Researchers have identified a possible way to treat cancers by uncovering a crucial molecular link between a viral infection and the development of a common and fatal form of liver cancer. In findings reported in the journal "Molecular Cell," the researchers at the University of Texas’ M.D. Anderson Cancer Centre traced the pathway by which the Hepatitis B virus (HBV) leads to development of Hepatocellular Carcinoma (HCC). The researchers found that HBV "turns off" an enzyme known as GSK-3, which acts to suppress tumour formation as well as inhibit the spread of cancer. — PTI Unusual meteorite
Prof Munir Humayun of the National High Magnetic Field Laboratory and the geological sciences department at FSU and Alan Brandon of NASA discovered an isotopic anomaly in the rare element osmium in primitive meteorites. The anomalous osmium was derived from small stars with a higher neutron density than that which formed our solar system. The findings of the researchers, who also included colleagues from the University of Maryland and Bern University in Switzerland, were recently published in the journal Science.
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THIS UNIVERSE Please explain why the intensity of ultraviolet rays on the earth is more during solar or lunar eclipse. This is a myth, without any physical reason. Somehow this physical sounding statement has been mixed with a whole lot of superstitions about eclipses. Some of the superstitions do not allow people to be out in the open; pregnant women are specially barred, there are restrictions on food, and there is a mass of ritual. All these are remnants of very ancient time when an eclipse was an unexpected, un-understood and therefore terrifying phenomenon. I have not heard so much about abundance of ultraviolet rays during a lunar eclipse, but such a statement in regard to a solar eclipse is quite common. Just remember what happens during a total solar eclipse. The shadow of the moon completely covers the sun preventing all rays, including the ultraviolet, from reaching the earth. Where is the possibility that greater flux of ultraviolet would hit the earth? But there is a reason for this misconception. When a complete solar eclipse occurs there is a great attraction/temptation for observers to stare in that direction and look at that magnificent happening. Since it is dark the irises of their eyes are fully open. And then the moon moves off a little and the bright limb of the sun appears, sending a strong dose of visible and ultraviolet energy on to the retinas of our eyes. Our great curiosity combined with negligence of not using appropriate filters can damage our eyes. That might be the source of the false statement that during a solar eclipse the ultraviolet light falling on the earth increases. Do watch the eclipse, but do not stare in that direction for long without adequate solar filters. Better still, watch it using a projected image. Kindly tell me how high do jets fly. As you go higher in the atmosphere the density of air decreases. This has two consequences affecting the flight of an airplane. Air resistance decreases, which implies that the rate of fuel consumption as also the stress on the structure of the airplane is less. This is good. But this helps only till the point where the upward thrust provided by the airflow on the specially shaped body and wings of the plane is enough to support its weight. That would also depend on the speed of the plane. Here another factor comes in. When the plane speed becomes equal to the speed of sound, shock waves are generated which put an enormous stress on the structure of the plane. Properly designed airframe can withstand that and if you have adequate power in your engines you can climb into the stratosphere (above 60,000 feet altitude) and travel at twice the speed of sound. However it has been found that for commercial passenger planes this is not very economical. There is another undesirable effect. A plane flying at speeds higher than the speed of sound drags a shock wave behind it making the life of people living in its path very uncomfortable — sonic booms are not very pleasant for the civilian population. Therefore, considering various tradeoffs discussed above the commercial jets cruise at an altitude of about 40,000 feet if they are going far or slightly less if the flight is not very long. The speed is kept somewhat lower than the speed of sound — around 900 kilometres per hour, while the speed of sound is around 1200 kilometres per hour. |
Earthquake
occurrences at Kashmir, Koyana, Jabalpur, Latur etc during recent
years vociferously proclaim that no part of earth is immune to seismic
activity.The Pacific Ring of Fire, the Alpine-Mediterranean — Trans
asiatic belt, Mid oceanic ridges in the Atlantic, Pacific and the
Indian Oceans and the Rift zones of Eastern Africa as well as East
Central Siberia are the most vulnerable parts. Two-thirds of our own
country lies in the seismic region of moderate to severe intensity.
The Peninsular India has been unknown for severe earthquakes but the
Koyana, Jabalpur and Latur earthquakes have complicated the problem,
though not beyond comprehension.
However,
the factors which we are still ignoring are the nuclear test
explosions, environmental degradation and man’s continuous
interference with the nature in the form of huge water reservoirs,
still rising skyscrapers, millions of flyovers, multistoreyed bridges,
countless tunnels, underground structures extension of metro railways,
blantantly changing land use patterns etc. These are the definite
reasons which we can no longer afford to ignore.
An
unusual meteorite that fell on a frozen lake in Canada five years ago
has led a Florida State University geochemist to a breakthrough in
understanding the origin of the chemical elements that make up our
solar system.