The waves that cause earthquakes are referred to as P-Waves and S-waves.
P-Waves or primary are identical in character to sound waves. They are high frequency, short wavelength, longitudinal waves which can pass through both solids and liquids. The ground is forced to move forwards and backwards as it is compressed and decompressed. This produces relatively small displacements of the ground. P-Waves can be reflected and refracted, and under certain circumstances can change into S- waves. The particles of P-waves are compressed and expanded in the waves direction.
S-Waves or secondary waves travel more slowly than P-Waves and arrive at any given point after the P-Waves. Like P-Waves they are high frequency, short-wavelength waves, but instead of being longitudinal they are transverse. They move in all directions away from their source, at speeds which depend on the density of the rocks they move through. They cannot move through liquids. On the surface of the earth, S-Waves are responsible for the sideways displacement of walls and fences. S-Waves move particles at 90 degrees to the waves direction.
Earthquakes are cause to much damage over the entire earth, they cause damage to both environment and to residential areas. Because earthquakes are a threat to humans, we are required to research them and come up with methods to predict when we can expect a quake to occur.
Earthquakes are a serious natural hazard in many parts of the world. They often seem to strike without warning, sometimes inflicting massive damage and casualties. Often they occur in predictable areas such as plate margins where earthquakes have occurred in the past, scientists are left with little to no option but to come up with a way to warn the public when this natural hazard could occur. Because earthquakes are so devastating, there is great interest in the study of predicting earthquakes. When scientists are predicting earthquakes they like to look at the size mainly and obviously the time and location. Scientist look mainly at forecasting earthquake that are going to happen in the near future, so people have as much time to evacuate as possible, although we are not able to predict individual earthquakes, the worlds largest earthquakes do have a clear spatial pattern, and forecasts of the location and magnitude of future large earthquakes can be made. Most large earthquakes occur on long fault zones around the margin of the Pacific Ocean. This is because the Atlantic Ocean is growing a few inches wider each year. And the Pacific is shrinking as the ocean floor is pushed beneath Pacific Rim continents. Geologically, earthquakes around the Pacific Rim are normal and expected. The long fault zones that ring the Pacific are subdivided by geologic irregularities into smaller fault segments which rupture individually. Earthquakes magnitude and timing are controlled by the size of a fault segment, the stiffness of the rocks, and the amount of accumulated stress. Where fault and plate motion are well known, the fault segments likely to break can be identified. If a fault segment is known to have broken in a past large earthquake, recurrence time and probable magnitude can be estimated based on fault segment size, rupture history, and strain accumulation. This forecasting technique can only be used for well-understood faults. Forecasting cannot be made for poorly-understood faults. People who live in earthquake zones need to be warned of near-future earthquakes, so they can be prepared and less destruction will be done. People can prevent maximum damage by using the ‘squat’ method, and building there houses low and wider, with deeper foundations, making it harder for the house to fall down in the occurrence of an earthquake.
There is nothing we as humans can do to prevent an earthquake from occurring, but we can research and try find new ways to prevent major casualties and monetary losses to an area struck by an earthquake. “one well known successful prediction was the Haicheng, China earthquake of 1975, when an evacuation order was sent out the day before an 7.3 rated earthquake on the Richter scale struck.” (Ludwin, R, 2002, Earthquake Prediction [on-line]).
In conclusion we have seen just how lethal and destructive an earth quake can actually be if occurs in a populated area. We see how humans are not the only ones affected, and how the environment is destroyed as well. Hopefully in the future, as the machinery becomes more scientific, we, as scientists would have found a more accurate method in predicting earthquakes, to prevent any further major casualties and destruction in the future.
References:
An Evaluation of the seismic-window theory for earthquake prediction, 1988. R.B. Schall, California Geology, vol.41,No.2,pp.41-45.
Earthquake Reasearch at Parkfield, California-National Earthquake Prediction
Earthquakes,2003, B.A. Bolt, W.H Freeman and Company, 331 p.
