 |
|
| SCIENCE & TECHNOLOGY |
|
|
|
Perils of thawing permafrost Squeezing more oil Prof Yash
Pal PROF YASH PAL
|
|
|
Could skyscrapers induce quakes? Putting forth this theory, Dr Cheng Horng Lin, a geologist from Taiwan, has said that Taipei basin was a stable area before the construction of the tallest building and the number of earthquakes in the area have increased since its completion. Dr Lin’s theory has put a question mark on the future of other skyscrapers under planning or construction in the world.
Earth and Tectonic Plates Before believing in Dr Lin’s theory, the composition of earth and the causes of earthquakes will have to be looked into again. Earth is made of four layers, inner core, outer core, mantle and crust. Inner core is solid metal of about 2450 km diameter. Outer core is liquid and 2150 km thick. Next comes Mantle, 2900 km thick and made of high temperature rock. The topmost layer is Crust having a thickness of 5 to 40 km, the oceanic crust being 5 to 10 km thick and continental crust 35 to 40 km thick. High temperature and pressure difference between the Crust and the Core cause masses of the Mantle to slide over Outer Core. These masses of Mantle are called Tectonic Plates. Earth’s surface has seven tectonic plates which keep moving in different directions thereby causing stress on adjoining faces of the plates. The “faults” lie at the adjoining faces of tectonic plates. Movement of plates causes stress in the faults. Whenever this stress becomes excessive, vibrations travel to the Crust causing earthquakes. The point inside Earth where an earthquake originates is called Focus. Point on Earth’s surface directly above the Focus is called epicentre. The depth of Focus is generally very high, in the range of 100 km. If less than 70 km, it is called shallow, if 70 to 300 km, it is called Intermediate and the one above 300 km is called deep depth of focus. Though most of earthquakes occur at depth less than 100 km, even the shallowest earthquakes are a few km deep below earth’s surface. Taipei101, located in Xin-Yi district of Taipei in Taiwan, is built over 80-metre-deep piles, 380 in number, each having 1500 mm diameter. 30 metre depth of piles penetrates into the bedrock. The load of Taipei101 is spread over an area of 3.7 acres. Whenever a building is constructed, the pressure that its load causes on the ground is calculated and compared with the bearing capacity of the soil below it. The type of foundation is chosen accordingly to keep the pressure less than the bearing capacity. Settlements allowed in the buildings are also very small. Howsoever high or heavy a building may be, pressure caused by it on the founding stratum will be within the bearing capacity at that level. The pressure distribution takes place in a bulb below the foundation, least of it being at the lowest point of the bulb. The pressure caused by Taipei101 even at a depth of 500 metres should be small, leave apart its effect at the depth at which earthquakes originate. In support of his argument, Dr Lin has also quoted the number of earthquakes taking place in Taipei101 area. Taipei101 is, in fact, already located in a highly active seismic zone. Relating the earthquakes occurring in that area to Taipei101 therefore is not justified. Moreover, worldwide, about 1.5 lakh earthquakes are recorded annually while 9.0 lakh of them go unrecorded. Under such circumstances, two or three micro-earthquakes occurring last year in Taipei101 area can’t be attributed to it. The theory put forth by Dr Lin, therefore, doesn’t hold good. Earthquakes originate from within the Earth and in comparison to the size and magnitude of earth, man’s activities are too small and can’t cause earthquakes. Construction of a skyscraper may cause movement of faults only if the stress caused by its load reaches the Focus zone below the earth. Howsoever high skyscrapers we may build, their weight can’t cause stress 10 km below ground surface. Construction of skyscrapers should, therefore, continue without a thought that these may cause earthquakes.
|
|
Perils of thawing permafrost Ancient roots and bones locked in long-frozen soil in Siberia are starting to thaw, and have the potential to unleash billions of tones of carbon and accelerate global warming, scientists have said. This vast carbon reservoir, contained in permafrost soil in northeastern Siberia, contains about 75 times more carbon than the amount released into the atmosphere each year by the burning of fossil fuels, the researchers said in a statement. Siberia isn’t the only place on earth with massive loads of permafrost. Parts of Alaska, Canada and northern Europe have them too. The Siberian area is possibly the world’s largest, covering nearly 400,000 square miles with an average depth of 82 feet and probably holds about 500 billion metric tons of carbon. By any measure, this is a lot, and it is in fact twice what scientists previously believed was there, says ecologist Ted Schuur of the University of Florida. “There’s a huge pool of carbon, even more than people thought before, perhaps double the amount of carbon that we thought,” said Schuur, one of the article’s co-authors. “If you have twice as much carbon there, essentially in the future twice as much could be released into the atmosphere.” Cars, power plants and other fossil fuel burners release at least six billion metric tons of carbon dioxide into the atmosphere annually, contributing to global warming, the scientists said. As the Siberian permafrost thaws, it will release the carbon contained in old grass roots and buried animal bones into the atmosphere, in what could be an unstoppable contributor to global climate change, according to the researchers. Earlier climate models may have failed to account for this possible component of global warming, he said. Schuur said this source of atmospheric carbon could create a vicious global warming cycle. “You have anthropogenic (human-generated) carbon that’s making things a little bit warmer, and that causes the permafrost to warm up and carbon is then released from the permafrost,” he said. “It goes into the atmosphere and makes things warmer yet again, so then more permafrost thaws.” If all Siberian permafrost thawed and released its carbon in the form of heat-trapping carbon dioxide, it could nearly double the 730 billion metric tons of carbon now in the atmosphere, the scientists said.
— Reuters
|
|
Squeezing more oil Creating artificial seismic waves, similar to those that occur during an earthquake, could help squeeze more oil from natural reservoirs. In addition to sending tremors that knock down buildings, earthquakes greatly increase the permeability of rocks to transmit fluids including oil. “Shaking increases permeability, Emily Brodsky, an assistant professor of Earth Sciences at the University of California, Santa Cruz, said in an interview. “Permeability governs how fluid flows through rock, whether it’s water or oil, so this has practical implications for oil extraction,” she added. Brodsky and her colleagues, who reported their research in the journal Nature, also found that the amount of permeability is directly related to the amplitude of the shaking. “Potentially if you could increase permeability you could greatly increase the available oil you could tap out of a reserve, she explained. One way of doing that, in principle, is by mimicking the effects of an earthquake but scientists do not understand the physics well enough, or how to tune the vibrations, to increase the flow of oil. One possibility would be to use vibroseis trucks that shake the ground to take a type of X-ray of the Earth to find out the structure of rocks and where the oil is located. “If we understood the physics of the permeability enhancement well enough, the vibrations could be tuned to increase with the flow of oil,” Brodsky added. The scientists made their discovery after studying 20 years of data of water seeping in and out of wells during seven earthquakes in an area of California. They noticed that every time an earthquake occurred the permeability jumped and the surrounding rocks became up to three times more permeable. A few months after the tremor the permeability returned to normal levels.
— Reuters Titan has methane lakes Scientists say they have found the first widespread evidence of giant hydrocarbon lakes on the surface of Saturn’s planet-size moon Titan. The cluster of hydrocarbon lakes was spotted near Titan’s frigid north pole during a weekend flyby by the international Cassini spacecraft, which flew within 950 km of the moon. Researchers counted about a dozen lakes ranging from 10 kilometres to 100 kilometres wide. Some lakes, which appeared as dark patches in radar images, were connected by channels while others had tributaries flowing into them. Several were dried up, but the ones that contained liquid were most likely a mix of methane and ethane.Titan is one of two moons in the solar system known to possess a significant atmosphere similar to primordial Earth. — AP
|
|
PROF YASH PAL
What is the reason for magnetic energy and gravitational force? This question cannot be answered simply or easily. It needs a fair amount of elaboration. Firstly, let me clarify that magnetism and gravity belong to different classes of forces. I say this in spite of the fact that ultimately one might find a way of describing all forces through a single unified theory — we are not there yet. The four classes of forces that seem to describe and govern most of the universe and its phenomena are 1) Gravitation, 2) Electro-magnetism, 3) the Weak force and 4) the Strong force. Gravitation is the most familiar because things fall down when released from a height. This is also the force between any two masses merely because they have mass. It is found that gravitation also affects light or radiation. Gravity describes the planetary motions and dominates when large masses are involved. Theory of gravitation associated with the name of Newton has been modified and refined by the General Theory of Relativity, though in the ordinary world the Newtonian gravitation is a fairly good approximation and suffices. You have asked for the reason for the gravitational force. It is possible that the existence of mass might be fundamentally connected with this. In the study of astronomy and cosmology there are hints that some more fundamental particles might account for gravitation being what it is. So the simple answer to your question is that I do not quite know. You must, of course, realise that it is like asking why should there be a universe like ours — why the sun and the earth, the stars and galaxies, why life and people? These are hard questions to answer, you would agree. You could almost say that one of the possible universes was the one we have, but there might be others with which we have no connection and where we would certainly be non-existent. Coming now to what you call magnetic energy. Incidentally where there is force, energy is also implied because when force acts energy is changed. This comes from the very definition of these two terms. Magnetism and electricity were unified some time ago. They are very elegantly described by a single theory. Wherever there are electric currents they also have magnetic fields. Movement of a conductor through a magnetic field produces electric current. All this is fairly well understood and extensively utilised in our homes and industry in general. In this case also one might state that the why of electromagnetism is understood from basic principles and symmetries. The universe seems to have a character in which, according to the current understanding, electromagnetism, the weak force responsible for phenomena like a radioactivity and the strong force that is responsible for structure and phenomena at the nuclear level have to be what they are, more or less. We still have some ways to travel to include gravitation in the world of this interdependence and inevitability. I am somewhat apologetic about giving the kind of answer I have given, but the fault lies with your irrepressible idle curiosity! I would suggest that we should try to confine our questions to things that we have ourselves discovered through our own observation and experimentation. |
A new controversy raging in the world is that two of the recent earthquakes could have been triggered by Taipei 101, the tallest building of the world. 508 metres high, Taipei 101 weighs 700,000 tonnes and it is believed that it has put so much stress on the ground below it that some earthquake fault could have been reopened.