The recent earthquake which spawned off a Tsunami made headlines all over the world for being one of the deadliest catastrophies in modern times taking over 250,000 human lives and damaging billions of dollars in property. The ?2004 Indian Ocean earthquake? at a magnitude of 9.0, was the largest earthquake since the 9.2 magnitude Good Friday Earthquake off Alaska in 1964, and tied for fourth largest since 1900. The earthquake originated in the Indian Ocean just north of Simeulue island, off the western coast of northern Sumatra, Indonesia. The resulting tsunami devastated the shores of Indonesia, Sri Lanka, India, Thailand and other countries with waves of up to 15m (50 feet) high, even reaching the east coast of Africa, 4500 km (2,800 miles) west of the epicenter.
The belief that wild and domestic animals possess a sixth sense and know in advance when the earth is going to shake has been around for centuries. Could it be true? Did animals sense Tsunami was coming?
According to eyewitness accounts, the following events happened:
Wildlife experts believe animals’ more acute hearing and other senses might enable them to hear or feel the Earth’s vibration, tipping them off to approaching disaster long before humans realize what’s going on. Relatively few animals have been reported dead, however, reviving speculation that animals somehow sense impending disaster.
An earthquake is a trembling or shaking movement of the Earth?s surface. Earthquakes typically result from the movement of faults (Faults are cracks in the earth where sections of a plate are moving in different directions.) within its uppermost layers. The solid earth is in slow but constant motion and earthquakes occur where the resulting stress exceeds the capacity of Earth materials to support it. Earthquakes occur every day on Earth, but the vast majority of them are minor and cause no damage.
Before we move onto the model of plates that our world is modelled on, let us understand the word ?Tectonic Plate?. Tectonic plates are nothing but the Earth?s crust (the outer layer of the planet) or Lithosphere. With plate tectonics the world is modeled as a collection of ‘dinner plates’ sliding past each other on the giant table of the earth, these are, in fact, cracked dinner plates, under high stress. Nearly all the relative motion takes place at the edges of the plates, but there are still the ‘creaks and groans of an ancient crust’. At times, motions along these interior weak zones produce rather large earthquakes.
Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don’t just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that’s built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.
Now that we know the fundamentals of earthquake, lets delve into the specifics of different types of earthquakes based on how they occur.
Events that occur at plate boundaries are called interplate earthquakes; the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes.
An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake with land deformations and resulting seismic waves which travel through the Earth and along the Earth’s surface.
An intraplate earthquake is an earthquake that occurs within the plate and can inflict heavy damage on towns and cities. Who can forget the large earthquake which devastated the region of Gujarat, India, in 2001, resulting in a large loss of life which was a result of a rare, large intraplate earthquake.
Explosions underground can also cause earthquake-like seismic waves. These explosions may be set off to break rock while making tunnels for roads, railroads, subways, mines or even while carrying out a nuclear test under ground. These explosions, however, don’t cause very strong seismic waves. You may not even feel them. Sometimes seismic waves occur when the roof or walls of a mine collapse. People near the mine can sometimes feel these. The largest underground explosions, from tests of nuclear warheads (bombs), can create seismic waves very much like large earthquakes.
Study of Earthquakes
Seismologists study earthquakes by going out and looking at the damage caused by the earthquakes and by using seismographs. A seismograph is an instrument that records the shaking of the earth’s surface caused by seismic waves. Most seismographs today are electronic, but a basic seismograph is made of a drum with paper on it, a bar or spring with a hinge at one or both ends, a weight, and a pen. The one end of the bar or spring is bolted to a pole or metal box that is bolted to the ground. The weight is put on the other end of the bar and the pen is stuck to the weight. The drum with paper on it presses against the pen and turns constantly. When there is an earthquake, everything in the seismograph moves except the weight with the pen on it. As the drum and paper shake next to the pen, the pen makes squiggly lines on the paper, creating a record of the earthquake. This record made by the seismograph is called a seismogram.
By studying the seismogram, the seismologist can tell how far away the earthquake was and how strong it was. This record doesn’t tell the seismologist exactly where the epicenter was, just that the earthquake happened so many miles or kilometers away from that seismograph. To find the exact epicenter, you need to know what at least two other seismographs in other parts of the country or world recorded.
Measurement of Earthquake
The magnitude of most earthquakes is measured on the Richter scale, invented by Charles F. Richter in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake, no matter what type of wave was the strongest. Although Richter originally proposed this way of measuring an earthquake’s “size,” he only used a certain type of seismograph and measured shallow earthquakes in Southern California. Scientists have now made other “magnitude” scales, all calibrated to Richter’s original method, to use a variety of seismographs and measure the depths of earthquakes of all sizes.
Another way to measure the strength of an earthquake is to use the Mercalli scale. Invented by Giuseppe Mercalli in 1902, this scale uses the observations of the people who experienced the earthquake to estimate its intensity.
Earthquakes really pose little direct danger to a person. People can’t be shaken to death by an earthquake. Some movies show scenes with the ground suddenly opening up and people falling into fiery pits, but this just doesn’t happen in real life.
The Effect of Ground Shaking
The first main earthquake hazard is the effect of ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake. Buildings can even sink into the ground if soil liquefaction occurs. Liquefaction is the mixing of sand or soil and groundwater (water underground) during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quicksand. If liquefaction occurs under a building, it may start to lean, tip over, or sink several feet. The ground shaking may also cause landslides, mudslides, and avalanches on steeper hills or mountains, all of which can damage buildings and hurt people.
The second main hazard is flooding. An earthquake can rupture (break) dams along a river. The water from the river or the reservoir would then flood the area, damaging buildings and maybe sweeping away or drowning people.
Tsunamis and seiches can also cause a great deal of damage. A tsunami is what most people call a tidal wave, but it has nothing to do with the tides on the ocean. It is a huge wave caused by an earthquake under the ocean. Tsunamis can be tens of feet high when they hit the shore and can do enormous damage to the coastline. Seiches are like small tsunamis which occur on lakes (that?s right Lakes) that are shaken by the earthquake and are usually only a few feet high, but they can still flood or knock down houses, and tip over trees.
The third main earthquake hazard is fire. These fires can be started by broken gas lines and power lines, or tipped over wood or coal stoves. They can be a serious problem, especially if the water lines that feed the fire hydrants are broken, too. For example, after the Great San Francisco Earthquake in 1906, the city burned for three days. Most of the city was destroyed and 250,000 people were left homeless.
Most of the hazards to people come from man-made structures themselves and the shaking they receive from the earthquake.
What Should YOU Do Before, During, And After An Earthquake?
Before an Earthquake
- Make sure you have a fire extinguisher, first aid kit, a battery-powered radio, a flashlight, and extra batteries at home.
- Learn first aid.
- Learn how to turn off the gas, water, and electricity.
- Make up a plan of where to meet your family after an earthquake.
- Don’t leave heavy objects on shelves (they’ll fall during a quake).
- Anchor heavy furniture, cupboards, and appliances to the walls or floor.
- Learn the earthquake plan at your school or workplace.
During an Earthquake
After an Earthquake
- Check yourself and others for injuries. Provide first aid for anyone who needs it.
- Check water, gas, and electric lines for damage. If any are damaged, shut off the valves. Check for the smell of gas. If you smell it, open all the windows and doors, leave immediately, and report it to the authorities (use someone else’s phone).
- Turn on the radio. Don’t use the phone unless it’s an emergency.
- Stay out of damaged buildings.
- Be careful around broken glass and debris. Wear boots or sturdy shoes to keep from cutting your feet.
- Be careful of chimneys (they may fall on you).
- Stay away from beaches. Tsunamis and seiches sometimes hit after the ground has stopped shaking.
- Stay away from damaged areas.
- If you’re at school or work, follow the emergency plan or the instructions of the person in charge.
- Expect aftershocks.
Earthquake is one of the most terrifying phenomena that mother-nature dishes out and is an expression of a living planet after millions of years of existence resulting in both human and monetary loss. So the next time you feel the earth shake below your feet, try to stay calm and use your best judgment of the situation by remembering some of the above tips to save yourself and your loved ones from harms way.
Author: Allen Martis- USA