When Atlas Shrugs
Rescue workers look for victims into a wrecked building in Chile.
The 8.8 magnitude earthquake that rocked Chile on February 27 caused the death of almost 1000 people. It was so powerful that scientists believe that it may have moved the Earth's figure axis of rotation by 3 inches and eventually shortened the length of the day by 1.26 microseconds (a microsecond is one millionth of a second). And as far as the size of the Earth is concerned, these are incredible lengths. Richard Gross, a scientist from NASA's Jet Propulsion Laboratory (JPL), armed with a complex mathematical model came up with a preliminary calculation, which he computed along with his fellow scientists, demonstrated that the length of the day as we know has been shortened as an effect of the 7th strongest earthquake ever to occur in recorded human history. This catastrophic incident also slightly changed the planet's shape and shifted the North Pole by centimetres. It must be mentioned here that earthquakes can involve shifting of hundreds of kilometres of rock by several metres, altering the distribution of mass on the planet. Even though the earthquake in Chile, which was 700-800 times stronger, but at a greater depth-21.7 miles, compared to the shallow 8.1-mile depth of the Haiti quake, will not affect the changing of the seasons. However the occurrence of two major earthquakes in less than two months sure is a concern for all earthlings and their worldly affairs.
In the past, strong earthquakes have altered the length of Earthly days and her rotation of axis as well. The 9.1 magnitude Sumatran quake in 2004, which set off a deadly Tsunami, is thought to have shortened Earth's days by 6.8 microseconds and shifted her axis by 2.32 milliseconds (about 7 centimetres or 2.76 inches). Scientists from the JPL applied the same model into the aftermath of Chilean quake that previously estimated the stated findings of the Sumatran quake.
All earthquakes as well as all worldly events even as simple as driving a vehicle to as complex as testing a nuclear bomb affect Earth's rotation. But generally, the changes are barely noticeable. Even though the earthquake in Chile was much smaller compare to the Sumatran one, but its effects on Earth are larger mostly due to location of its epicentre. And scientists believe this is why the Chilean earthquake shifted the Earth's figure axis more than the Sumatran event. According Dr Gross, two reasons are at play here. First and foremost, unlike the 2004 Sumatran earthquake, where he epicentre was near the equator, the 2010 Chilean earthquake was located in Earth's mid-latitude, which is why the devastating incident of the later was more effective in shifting the Earth's figure axis. Secondly, the fault line responsible for Chilean quake dips into Earth at a slightly steeper angle than that of the 2004 Sumatran earthquake. Thus the Chile fault line was more effective in moving Earth's mass vertically and hence more effective in shifting Earth's figure axis.
Now, what is this figure axis? It must be noted that Earth's figure axis should not be confused with the North-South axis (the imaginary lines going through the poles, the line that planet Earth tilts and rotates on) which spins around once everyday at a speed of about 1,000 mph. The figure axis is the axis around which the Earth's mass is balanced which is offset from the Earth's north-south axis by about 33 feet. Dr David Kerridge, the head of Earth Hazard and Systems at the British Geological Survey, explained how the Chilean earthquake may have caused the changes in the Earth's figure axis by 8 centimetres or 3 inches. In his own words: “It's what we call the ice-skater effect. As the ice skater puts when she's going around in a circle, and she pulls her arms in, she gets faster and faster. It's the same idea with the Earth going around if you change the distribution of mass, the rotation rate changes”. Dr Gross along with Dr Benjamin Chao of NASA's Goddard Space Flight Center also studied the changes in the polar motion after the earthquake in Chile and found that the “mean north pole” was shifted by about 1 inch (2.5 centimetres) in the direction of 145° East Longitude. The distinguished scientists also discovered that the quake also affected Earth's shape as they found that the Earth's oblateness (the flattening shape on the top and bulging at the equator) decreased by a small amount, about one part in 10 billion, continuing the trend of earthquakes making Earth less oblate.
About 500 million years ago, our 4.5 billion year old Earth had a day that was only 22 hours in length. Since then the number has grown about 2 hours to 86,400 seconds. Surely, this planet has come a long way and her habitual natural events (no matter how upsetting they are) are simply parts of the days of every earthling. One crucial factor with earthquake though, and that is no matter how strong the quake is, often times the extent of the devastation depends on the nature of man-made establishments that human beings architected and engineered on the surface at the first place. As expected, the concern of Bangladesh and her capital of concretes come into mind every time such disaster occurs and one can't help but to shiver in fright realising the extent of damage that an earthquake of such strength could cause to already deteriorating capital of the country. Many experts have even stressed on the inevitability of such natural phenomena. What is expected from the authorities is to learn and better themselves as far as the process of lessening the damage and preparation of all-out relief and rescue efforts are concerned.
(R) thedailystar.net 2010