 |
|
| SCIENCE & TECHNOLOGY |
|
|
|
Earthquakes, tsunamis and plate tectonics
Small but deadly
|
|
|
|
Earthquakes, tsunamis and plate tectonics Geologists define an earthquake as the shaking or trembling caused by the sudden release of energy, usually as a result of faulting, which involves displacement of rocks along fractures. Earthquakes indicate that the earth is an internally active planet. Most earthquakes take place at well-defined zones at transform, divergent and convergent plate boundaries. There is an interesting relationship between earthquakes and plate boundaries (fig. 1) About 80 per cent earthquakes occur within the circum-Pacific belt, 8 per cent within the Mediterranean-Asiatic belt and the remaining 5 per cent within plate interiors or along oceanic spreading ridges. Most of the earthquakes result from convergence plate boundaries. The circum-Pacific belt is well known for both its volcanic activity and its earthquakes. About 60 per cent of all volcanic eruptions and 80 per cent of all energy released by earthquakes take place in this belt, that is why it is known as the “Ring of Fire”, alluding to a large number of volcanoes. The amount of damage and people’s reaction to an earthquake are used to determine an earthquake’s intensity according to the modified Marcelli intensity scale. The Richter magnitude scale and the Marcelli intensity scale are used to express the amount of energy released during the earthquake. Great hazards are associated with earthquakes such as ground shaking, tsunamis, fire and ground motion. Tsunamis, a Japanese term meaning “harbour wave”, are in fact seismic waves. They are destructive sea waves generated when a large amount of energy is rapidly released in the body of water. Many result from submarine earthquakes, volcanoes at sea or submarine landslides. Tsunamis have a long wavelength and travel across the open sea at high speed. As tsunamis approach the shore, their wavelengths decrease, and their wave height increase. Therefore, tsunamis can be formidable agents of destruction along shore lines. Once a tsunami is generated it can travel across the entire ocean and cause destruction far away from its source. In open sea, tsunami travel at several hundred kilometres per hour and commonly go unnoticed as they pass beneath the ships, because they are usually less than one metre high, and the distance between wave crest is typically hundred of kilometres. When they enter shallow water, the wave slows down and water piles up to height anywhere from a metre to 15 to 30 metres. They exert an enormous force against the shore and can inflict serious damage and great loss to life. Tsunamis differ from wind-produced ocean waves in that energy is transmitted to the waterfront from a sea floor disturbance, so that the entire ocean depth of water participates in the wave motion. Tsunami Early Warning System: On April 1, 1946 a tsunami originated in the Aleutian trench off the island of Unimak hit Hawaii. Moving at an average speed of 760 km per hour, the tsunamis reached the Hawaiian islands, 3200 km away in less than five hours. Because the wavelength was 150 km, the wave crest arrived about 15 minutes apart. As the waves approached the island, their height increased to at least 17 metres and thus produced an extremely destructive surf which swept inland and demolished houses, trees and almost everything in its path. Following this tragedy, US Coast and Geodetic Survey established a Tsunami Early Warning System in Honolulu. The system consists of seismographs and instruments that can detect earthquake-generated waves. Whenever a strong earthquake occurs anywhere in Pacific basin, its location is determined and instruments checked to see if tsunami has been generated. If it has, a warning is sent out to evacuate people from low-lying areas that may be affected. Nevertheless, tsunamis remain a threat to people in coastal areas, especially around the pacific ocean. One of the nature’s warning signs of approaching tsunami is that some are preceded by a sudden withdrawal of the sea from a coastal region. In fact, the sea might withdraw so far that it cannot be seen and the sea floor is laid bare over a huge area. A tsunami in about 1390 BC, coupled with the volcanic eruption that caused it, may have contributed to the demise of the Minoan civilisation on Crete. The writer is Professor, Geology Department, Panjab University. |
|
Small but deadly It is not easy to dismiss such fears over the possible health effects of nanotechnology — the science of the very small, at the scale of a billionth of a metre. There may be no evidence of risk, but that does not mean that the risk is zero. In fact, only now are scientists beginning to shed some light on exactly how the specially engineered nanoparticles, which are the basic ingredients of nanotechnology, might affect our health if they managed to end up in the wider environment. Much of this research is based on the round assembly of 60 carbon atoms known as the buckyball, or fullerene. This nanoparticle is considered important because it is a building block for all sorts of new materials and medicines. Buckyballs have remarkable characteristics. If you shoot one of these virus-sized particles at a steel plate at 15,000mph, it bounces back unharmed. Squash one, and it becomes twice as hard as diamond. They’re hollow, so you can put other molecules, such as drugs, inside them. But studies suggest that the properties that may make fullerenes useful may also make them toxic. The first evidence came earlier this year when Eva Oberdorster, an American toxicologist at the Southern Methodist University in Dallas, published a study showing how, after two days of swimming in water containing buckyballs, largemouth bass fish suffered damage to the fat membranes in their brains. Their livers had responded as though there was a toxin present. Now, scientists at Rice University, Houston, have pinpointed what could be the mechanism causing this damage. Rice’s breakthrough study, published in the journal Nano Letters, is the first to look at the toxic effects on individual human cells exposed to fullerenes, and the first to indicate the cause. “People have shown there’s a hazard, but this is the first work about how that hazard comes to be. It’s important for the community to understand how, because then you can change it,” says Kristen Kulinowski, the director of Rice’s Centre for Biological and Environmental Nanotechnology. They measured how many cells died within 48 hours, and repeated the tests until they found the exposure level for each solution that killed half the cells. The plain buckyballs destroyed half the cells in a concentration of about 20 parts per billion, but a concentration of 10 million times more was needed to make the modified fullerenes as toxic. By arrangement with The Independent
|
|
Understanding the Universe What do you think would be the consequences of so much emphasis on software development in India, and an absolute neglect of fundamental research? Software development is a laudable pursuit. The purpose of developing any software is to use it along with hardware to achieve an objective. Much software is designed to make hardware more potent, useful and productive. The productive purposes are primarily determined by those who are in the driving seat. Most such entities are users, producers or peddlers of hardware. Therefore, I am convinced that ascendance of software alone cannot be a permanent feature in any self-respecting economy. We also find that there is a great temptation for pushing our bright people into the labor market of low-grade software because our people can work for less money than those of the industrialised countries. In addition, a lot of our young people are being engaged in information technology enabled services (call centres and the like), mostly for people of the advanced countries. I suppose this is all right for the purpose of giving clerical jobs to some of our young people, but this should certainly not be categorised as knowledge work. Yes, we should be developing software, but more and more of it should be “high-end”. It should be for doing new things, designing new systems and creating new technology, including technology that would be most needed by our own a country. And we should not make even such high-grade activity an excuse for neglecting hardware design and manufacture. I am disturbed that of late, the manufacturing industry in India has been on decline. There’s hardly anything that we have designed ourselves that is manufactured and marketed worldwide. Things that have been designed have not been picked up by our industry, which has got into the habit of riding on foreign brand names. One aspect of the present attitude worries me even more, since I believe we are in danger of mortgaging our future. If all our bright students move away from science and engineering research, attracted by the lure of so-called software, followed by sales, finance and general management with a foreign or hyphenated Indian-Foreign company, there would not be an Indian identity left in tomorrow’s world. Some might think that is a desirable direction to pursue. On my part, I would begin to question the need and relevance of the century-long enterprise that was our freedom struggle. When I sit on a merry-go-round and then get off, why do I continue to experience the sensation of circular motion? You have asked a simple question that hides some beautiful complexity. We seldom wonder about the marvelous mechanisms and methods that keep us functioning. The question you have asked is intimately connected to the mechanism that provides us with a sense of balance. Let me see if I can put across some understanding of the equipment that provides us with this capability without using specialised anatomical jargon. I will also avoid detail, partly because I am myself not so well educated in this area. Inside both our ears there are three semicircular canals, oriented in three mutually perpendicular planes. These canals happen to be positioned at that location, but have little connection with the function of hearing itself. This location seems to have been chosen for its convenience — on two sides of the head and close enough to the communication lines of the central nervous system and the spinal routes that provide reflex action. Reducing this balancing system to a simple physical analogue, we could describe it the following way: The mutually perpendicular semicircular tubes are filled with a slightly viscous liquid. On the walls of the tube are a large number of tiny hair whose bending would alter a signal going to the nervous system, which controls the position of the head, pointing of the eyes etc. Let the tubes also contain a ball, or something with inertia that can move in the viscous fluid. Now rotate the head, say in a horizontal plane. The ball in the horizontal tubes would lag behind and would appear to move in a direction opposite to that of the head, or the canal. This would stimulate the hair by bending it backwards. Your sense of being on a merry go round would be derived from the signals originating therefrom. When the merry go round stops, the ball will keep going for a while, because of inertia, sending signals in the opposite direction, giving you a giddy feeling and upsetting your sense of balance. Remember that you have these tubes in three perpendicular directions. This would make you sensitive to disturbances in all the directions. With this simplified description, it should be possible to understand the experience of the kind you have mentioned or others, such as motion sickness or disorientation of astronauts during and after space flight. Apparently, the reason that some people (like me) suffer from vertigo is also due to the fact that my semicircular tube apparatus is partially faulty. From a physical point of view, the basic elements seem to be the following: 1. Three semicircular tubes, oriented in mutually perpendicular directions to cover all kinds of head movement. 2. Two sets of these tubes, one on each side of the head, close to the inner ear 3. Some fluid in the tubes and large number of fine hair sticking in, whose disturbance produces or modulates signals and 4. A ball-like object, heavier than the liquid in which it is suspended, to provide relative motion with respect to the tube during acceleration and deceleration. The rest is just signal processing and moving apparatus like muscles and pivoted bone levers. The whole of this marvelous system is known as the “vestibular” system. How do ants figure out where they have to go after they have collected food? When ants move around, they can mark their path with an odorous substance — something that other ants (and they themselves) can smell. That is the reason why, on a food-acquiring mission, they travel purposely along the trail laid by their leader. That is also the way they find their way home. If someone gets lost, a random walk brings it across a trail and a way home. I am sure many other complex messages are exchanged as well, enabling the intense degree of cooperativity we observe in their behaviour. If you see a line of ants going someplace, you can try to see the effect of wiping out their trail with detergent. It would take them quite a while before the train begins to move again.
|
||
|
New products & discoveries THE SETI Institute predicts that we’ll detect an extraterrestrial transmission within 20 years. If that turns out to be true, it’ll probably be the folks at UC Berkeley’s Hat Creek radio observatory who will have heard the call. Right now, the Allen Telescope Array of more than 300 dishes is under construction at Hat Creek five hours north of San Francisco. Within a year, the first 30 dishes will be operational, forming the basis of a giant ear that listens for intelligent beings in space while simultaneously gathering data for groundbreaking astronomy research. Way to foretell quakes?
Patterns of deep, prolonged tremors newly revealed beneath the San Andreas fault zone may offer scientists a way to foretell earthquake activity there. The small tremors don’t produce typical seismic vibrations that indicate a sudden slip along a fault, says Robert M. Nadeau, a seismologist at the University of California, Berkeley. Instead, the deep tremors gradually rumble to life. During a 3-year period that ended in December 2003, instruments detected 110 such events along a 30-kilometer-long stretch of fault centered just southeast of Cholame, in south-central California. The tremor episodes, all of which were too weak to be felt by people, originated at depths of 20 to 40 km and lasted from 4 to 20 minutes, says Nadeau. In contrast, sudden slips along the San Andreas fault typically occur at depths of less than 13 km and last less than a minute. |
IN his novel Prey, Michael Crichton portrayed a future threatened by minuscule, self-replicating robots that begin to consume the planet. That’s still in the realm of science fiction, but not everyone believes that nanotechnology is inherently safe. The Prince of Wales, for instance, warned us a year ago that the unleashing of small-scale “nano” particles on an unprepared world could result in a Thalidomide-like health disaster.