Surface Of The Earth By Earthquake Waves example essay topic

Earthquakes Earthquakes, one of the most destructive natural phenomena, consist of rapid vibrations of rock near the earth's surface. Because of their unpredictable occurrence and enormous capacity of destruction, they have brought fear to mankind since ancient times. A single shock usually lasts no more than a few seconds, but a series of smaller quakes may last for as long as five minutes. The quake felt on the surface is always the result, not the cause of some underground geologic process, and in many cases the damage done is immense. The Greek word for shaking, and (when applied to the earth) earthquake, is seism os.

Therefore, the science of earthquakes is called seismology (World Book Dictionary 1985). Earthquakes have been recorded as early as 526 A.C., but seismology is comparatively new. Until the 18th century, few accurate descriptions of earthquakes were recorded, and little was known about what caused them. When seismology was introduced it was learned that many earthquakes are the result of sea floor spreading, but most are caused by volcanic eruptions and plate tectonics. The plate tectonic theory explains that the earth is made up of 20 different plates that are always moving slowly past each other. This action pulls and compacts the plates, creating intense forces that cause the plates to break.

This, in turn, causes earthquakes. The energy released then travels along fault lines in seismic waves (World Book Encyclopedia). Seismic waves are either P-waves (primary), or S-waves (secondary). P-waves create a relatively low wave train and arrive at the surface first. On the surface they create a push-pull effect, thus moving the surface up and down. Their low amplitude and vertical movement create an effect much like a dangling slinky.

S-waves arrive second and are much more damaging. The high amplitude of S-waves, combined with their horizontal movement cause crippling effects on the earth's surface and man made structures (Watkins, Bottino, and Morisawa 30-32). Earthquakes occur around us all the time. Most are too small to notice and cause little to no damage. However, every so often large earthquakes do occur. Large earthquakes leave catastrophic damage and have brought death tolls up to 850,000 (World Book Encyclopedia).

The majority of death and destruction is the effect of the secondary shocks. Fires, landslides, tsunami, falling rock, damaged buildings, and damaged gas lines are just a few results of secondary shocks. These conditions reek havoc on earthquake corrupted areas, and in 1934, Bihar-Nepal witnessed this first hand. During a landslide, '... an observer reported that his car sank to the axles'. In 1946 off the coast of the Aleutians, the base of a lighthouse ended up 45 feet below sea level after a tsunami wave over 100 feet crashed on shore (Watkins, Bottino, Morisawa 51, 53-54). An earthquake is a natural occurrence; a phenomena just like rain.

They have occurred for billions of years and descriptions as old as recorded history shows their effects on people's lives. Long before scientific explanations mankind created folklore to explain them. We have come a long way for spinning yarns around the campfire, but there is still no way to prevent earthquakes. All in all it doesn't hurt to learn as much as one can, but just like taxes and pokemon earthquakes are something we have to live with. EARTHQUAKE REFERENCE FILES Earthquake, shaking of the earth's surface caused by rapid movement of the earth's rocky outer layer. Earthquakes occur when energy stored within the earth, usually in the form of strain in rocks, suddenly releases.

This energy is transmitted to the surface of the earth by earthquake waves. The study of earthquakes and the waves they create is called seismology. Scientists who study earthquakes are called seismologists. (Webster's p. 423) The destruction an earthquake causes, depends on its magnitude or the amount of shaking that occurs. The size varies from small imperceptible shaking, to large shocks felt miles around. Earthquakes can tear up the ground, make buildings and other structures collapse, and create tsunamis (large sea waves).

Many Lives can be lost because of this destruction. (The Road to Jaramillo p. 211) Several hundred earthquakes, or seismic tremors, occur per day around the world. A worldwide network of seismographs detect about one million small earthquakes per year. Very large earthquakes, such as the 1964 Alaskan earthquake, which measured 8.6 on the Richter scale and caused millions of dollars in damage, occur worldwide once every few years. Moderate earthquakes, such as the 1989 tremor in Loma Prieto, California (magnitude 7.0), and the 1995 tremor in K^one, Japan (magnitude 6.8), occur about 20 times a year. Moderate earthquakes also cause millions of dollars in damage and can harm many people.

(The Road to Jaramillo p. 213-215) In the last 500 years, several million people have been killed by earthquakes around the world, including over 240,000 in the 1976 T'ang-Shan, China, earthquake. Worldwide, earthquakes have also caused severe property and structural damage. Good precautions, such as education, emergency planning, and constructing stronger, more flexible structures, can limit the loss of life and decrease the damage caused by earthquakes. (The Road to Jaramillo p. 213-215,263) AN EARTHQUAKES ANATOMY Seismologists examine the parts of an earthquake, like what happens to the earth's surface during an earthquake, how the energy of an earthquake moves from inside the earth to the surface, and how this energy causes damage. By studying the different parts and actions of earthquakes, seismologists learn more about their effects and how to predict ground shaking in order to reduce damage. (On Shifting Ground p. 109-110) Focus and Epicenter The point within the earth along the rupturing geological fault where an earthquake originates is called the focus, or hypocenter.

The point on the earth's surface directly above the focus is called the epicenter. Earthquake waves begin to radiate out from the focus and follow along the fault rupture. If the focus is near the surface between 0 and 70 km (0 and 40 mi.) deep shallow focus earthquakes are produced. If it is deep below the crust between 70 and 700 km (40 and 400 mi.) deep a deep focus earthquake will occur. Shallow-focus earthquakes tend to be larger, and therefore more damaging, earthquakes. This is because they are closer to the surface where the rocks are stronger and build up more strain.

(The Ocean of Truth p. 76 & The road to Jaramillo p. 94-97) Seismologists know from observations that most earthquakes originate as shallow-focus earthquakes and most of them occur near plate boundaries areas where the earth's crustal plates move against each other. Other earthquakes, including deep-focus earthquakes, can originate in subduction zones, where one tectonic plate subduct's, or moves under another plate. (The Ocean of Truth p. 54-56) I Faults Stress in the earth's crust creates faults places where rocks have moved and can slip, resulting in earthquakes. The properties of an earthquake depend strongly on the type of fault slip, or movement along the fault, that causes the earthquake.

Geologists categorize faults according to the direction of the fault slip. The surface between the two sides of a fault lies in a plane, and the direction of the plane is usually not vertical; rather it dips at an angle into the earth. When the rock hanging over the dipping fault plane slips downward into the ground, the fault is called a normal fault. When the hanging wall slips upward in relation to the bottom wall, the fault is called a reverse fault or a thrust fault. Both normal and reverse faults produce vertical displacements, or the upward movement of one side of the fault above the other side, that appear at the surface as fault scarps. Strike slip faults are another type of fault that produce horizontal displacements, or the side by side sliding movement of the fault, such as seen along the San Andreas fault in California.

Strike-slip faults are usually found along boundaries between two plates that are sliding past each other. (Plate Tectonics p. 49-53) II Waves The sudden movement of rocks along a fault causes vibrations that transmit energy through the earth in the form of waves. Waves that travel in the rocks below the surface of the earth are called.