Thursday, April 23, 2009


Do you know how earthquakes arise? Things such as Elastic Rebound theory, Major earthquake zones, How big seismic waves are, locating earthquakes, earthquake measurement, Destruction to buildings and properties, Tsunamis, Earthquake warnings and predictions, and earthquake safety, all have a part in preparing and knowing how to deal with a earthquake situation; also knowing what makes a earthquake come to pass.

Geologists explain many earthquakes by the elastic rebound theory. According to this theory, the rocks on each side of a fault are moving slowly. If the fault is locked, stress in the rocks increases. When they are stressed to a certain point, however, the rocks fracture, separate at their weakest point, and spring back to their original shape, or rebound. Alas the reason for calling it the elastic rebound, because they bounce back to their original state of being unstressed.

Many times when the rocks fall into new positions they release energy in a form of vibrations called seismic waves. That release of energy often causes stress to other rocks; they break and come back to their original state. This is often the reason that huge earthquakes are followed by a series of small upheaval called aftershocks. Where the fault is, the first slippage occurs, and that is called the focus of the earthquake. And the epicenter is located right above the focus. Most earthquakes have a shallow focus.

Most earthquakes occur near the earths lithospheric plates. So it often show that the theory of plate tectonics is somewhat true. The earth has three major subduction zones. The first is a large area called the pacific ring of fire, this includes north and south America the east coast of Asia, and the western pacific islands of the Philippines, Indonesia, New Guinea, and New Zealand. Most of the plates are being sub ducted, while some plate scrape past each other.
The second major earthquake zone is along the mid ocean ridges. They occur there because the oceanic crust is pulling away from both sides of each ridge. This creates stress along the major ocean ridges.

The third major earthquake zone is the Eurasian-Melanesian mountain belt. Mountains along that region were formed by a collision between the Eurasian plate and the African, and Indian plates. Those plate are still colliding, and the same forces are still producing numerous earthquakes.

Scientists have determined that every earthquake produces three major types of seismic waves, each type travels at a different speed and causes different movements in the earths crust. Primary waves or p-waves move the fastest and are the first to be recorded by a seismograph. They may travel through liquids and solids. P waves also cause rock particles to move together and apart along the direction of the waves. Secondary waves or S-waves are the second waves to be recorded on the seismograph. S waves can only travel through solid material. S waves cannot be detected on the side of the earth that is opposite of the earthquakes epicenter: They cannot be detected because they do not penetrate through the earths liquid outer core. S waves cause rocks to move at right angles to the direction in which the waves are traveling. Long waves or L-waves are the slowest moving waves and they are the last to be recorded on the seismograph. L waves travel slowly, similar to ocean waves.
The way scientists find the epicenter of an earthquake, scientists analyze the arrival times between P waves and S waves. If the S waves arrive soon after the P waves, that means that the earthquake must have originated fairly close to where the seismograph station. To find out how far an earthquake is from a certain seismograph station, the scientists plot the difference between the arrival times of both the waves. For scientists to locate the epicenter of the earthquake, they need information from at least three seismograph stations at different locations.

To measure an earthquake, scientists use a richer scale to note the magnitude of and earthquake. A major earthquake, one that causes widespread damage, has a magnitude of 7 or above. A moderate earthquake has a magnitude between 6 and 7, And a minor earthquake, between 2.5 and 6. Earthquakes with magnitudes of less that 2.5 are called micro quakes, which usually are not felt by people. The mercalli scale says that intensity of an earthquake, or the amount of damage it causes, and a description. And earthquake with a rating of II , this has low intensity, and is, “Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.” One with a higher rating, like if it were rated X, is described as follows, “Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked, rails bent, shifted sand and mud.” The highest rating would be XII and means “total destruction.”
Destruction to buildings and such, can be prevented. Because buildings with week walls may completely collapse, some may even fall over. A building constructed in loose soil is more likely to be damaged, opposed to one that is built on solid ground; Because during an earthquake, the soil moves around like jelly. Then the building may proceed to sway violently and fall over. Most buildings are not designed to with stand the swaying motion caused by earthquakes. Most things are not constructed to withstand an earthquake, but nowadays they are testing the ground, and things like that to make sure it would be safe to build certain objects in certain areas.

A tsunami is major earthquake with an epicenter on the ocean floor and sometimes causes a giant ocean wave. Tsunami comes from Japanese and means “harbor Wave.” Two things are factors in tsunamis; Faulting and underwater landslides, and severe underwater landslides. Faulting may cause a sudden drop or rise in the ocean floor, a large mass of water also rises or drops. This mass of water goes up and down and it adjusts to the change in sea level. The more violent water goes into a series of long waves that develop into tsunamis. Disastrous earthquakes and tsunamis have encouraged the expansion and improvement of the Seismic Sea Wave Warning System. Scientists have numerous seismographs stations on the pacific ocean, and they can issue warnings immediately to the areas that may be affected. However, there will not be enough time to issue tsunami warnings to areas very near the epicenter of the earthquake.

Scientists have dreamed of being able to one day accurately prediction earthquakes. One of the earliest ways of prediction was watching animals; People knew that just before an earthquake, animals appear nervous and restless, almost as if they could sense the coming catastrophe. Scientists can make approximate predictions of future earthquakes, but may be off a few years. To make more accurate predictions, scientists are studying changes in the earths crust that can signal an approaching earthquake. Along some faults, scientists have identified zones of immobile rock called seismic gaps; it takes place where the fault is locked and unable to move. Scientists think that seismic gaps are future locations for earthquakes, due to stressed rocks. Several gaps that exist along the San Andreas Fault will probably be sites for earthquakes in the future. Scientists can detect a slight tilting of the ground, shortly before an earthquake. Some earthquakes are preceded by a decrease in the speed of local p-waves. Evidence suggest that the longer the decrease in speed lasts, the longer the earthquake will be. Most scientist would like to be able to control earthquakes. In fact, tests at Rangely, Colorado, showed that when water as injected along a fault, friction was reduced and the earthquake was less severe.

Destructive earthquakes may occur in any part of the united states, very destructive earthquakes are most likely to happen in California or Alaska; mainly be cause they are located on a fault, The Pacific Ring of Fire. Before an earthquake occurs, be prepared. Keep canned food, bottled water, flashlights, batteries, and a portable radio. Please don’t forget a manual can opener, most people don’t think of that until they can’t do anything about it anymore. During an earthquake, stay calm. Most of the time there are a few seconds between shaking, so that you may find a safer location. Stand in a doorway, or crouch under a desk, so that falling debris may not fall on you. If you are in a car, stay in your car, but be sure to be far away from buildings which may collapse. After a earthquake, be alert. Check for safety and health hazards. Always wear shoes around broken glass. Don’t touch things such as downed wires and things.

In conclusion, earthquakes have been intriguing us for some time now, but hope fully we will be able to predict where they will strike, plan ahead; safety precautions. In the future we may find out how and why to stop earthquakes from happening. But all in all, earthquakes are fascinating, and may be vile at the same time.

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