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 seismos. 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 a...
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...On shifting ground p.17-19) Earthquakes that occur in the area surrounding the Pacific Ocean, at the edges of the Pacific plate, are responsible for an average of 80 percent of the energy released in earthquakes worldwide. Japan is shaken by more than 1000 tremors greater than 3.5 in magnitude each year. The western coasts of North and South America are very also active earthquake zones, with several thousand small to moderate earthquakes each year. (U.S.G.S.) Intraplate earthquakes are less frequent than plate boundary earthquakes, but they are still caused by the internal fracturing of rock masses. The New Madrid, Missouri, earthquakes of 1811 and 1812 were extreme examples of intraplate seismic events. Scientists estimate that the three main earthquakes of this series were about magnitude 8.0 and that there were at least 1500 aftershocks. (The ocean of truth p.67-69)
Bibliography
"Earthquake” World Book Encyclopedia. Vol. 6. 1987.
"Seismos." World Book Dictionary. Vol. L-Z. Ed. Barnhart, Clarence L., and Robert K. Barnhart. 1987 Watkins, Joel s., Michael L. Bottino, and Marie Morisawa.
Our Geological Environment. Philadelphia: W.B. Saunders Company, 1975.
Earthquakes are a natural part of the Earth’s evolution. Scientific evidence leads many geologists to believe that all of the land on Earth was at one point in time connected. Because of plate tectonic movements or earthquakes, continental drift occurred separating the one massive piece of land in to the seven major continents today. Further evidence supports this theory, starting with the Mid-Atlantic ridge, a large mass of plate tectonics, which are increasing the size of the Atlantic Ocean while shrinking the Pacific. Some scientists believe that the major plate moveme...
could be used to explain and illustrate that previous theories were not entirely correct (Merali and Skinner, 2009, p.253). Through the analyzation of arrival times of these waves, Oldham had drawn an conclusion that p waves and s waves react differently in terms of being refracted, reflected or absorbed depending on the state of the material as shown in Figure 1.(Tarbuck, Lutgens, Tasa, 2013, p.143). Oldham had developed this theory of the Earth not being the same state due to these effects of seismic discontinuity which are shown in Figure 1., consisting of refraction, reflection and absorption. The changes that are displayed from this idea are; the speed of the waves due to a refraction occu...
Earthquakes in California are certainly not a surprise. What is a surprise is their unpredictability and randomness. Geologists say there is roughly a 50 percent chance that a magnitude 8 or more quake will hit the Los Angeles area sometime over the next 30 years. And, over the past twenty years, the Los Angeles area has witnessed several earthquakes, and in particular, two that were quite devastating; the 1971 San Fernando earthquake, and the January 17, 1994, Northridge Earthquake. Given the certainty that earthquakes will occur, they still seem to come as a surprise, and leave many communities unprepared to deal with their aftermath.
Since record keeping began, sometime in the 18th century, there have been 13 major earthquakes along the San Andreas Fault. However, radiocarbon dating has proved that earthquakes have been happening along the fault for thousands of years. The earliest recorded earthquake happened on July 28, 1769, and was experienced by Spanish explorer Gaspar de Portola while he camped along a small lake he named “San Andreas Lake”. Other notable early earthquakes occurred in 1836, 1838, 1865, 1868, and 1890. Unfortunately, there is no seismographic data recorded for these early earthquakes since it was not until 1887 that seismographs began being used in the United
Heller, Arnie. "The 1906 San Francisco Earthquake." Science & Technology (2006): 4-12. Web. 8 May 2014.
Earthquakes are best described as a shaking or vibration of the ground caused by breaking of rock. Sometimes they are very strong and other times you would hardly notice them. This shaking occurs when stress that builds up in the crust is suddenly released as the crust breaks free and/or slides against the other pieces of crust. Earthquakes may also be thought of as the breaking of a popsicle stick by applying pressure to both ends at the same time. Should you try this experiment , you will feel the pressure build up as you apply more force until the stick snaps. When the stick snaps you will feel an instant of pain at your fingers as the stress reduces and energy waves move throughout the stick. When the earth's crust is placed under similar types of stress, binding as the stress builds, it will also snap and release the energy into the surrounding rocks, 'ooch'. Thinking about earthquakes will become more clear if you try another experiment.
From studying the science behind the San Francisco earthquake, scientists have made a number of important discoveries involving how earthquakes function. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared each other at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”) (“The Great 1906 Earthquake and Fires”). A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”) (“The Great 1906 San Francisco Earthquake”). In fact, the earthquake could be registered in a seismograph on Capetown, South Africa, an astounding 10,236 miles away...
Before examining the Northridge event, understanding the naturally occurring hazard that is an earthquake will help to better understand exactly what happened and why it was such an important geological event. With four distinct layers, two layers, the crust and upper portion of the mantle, compose the skin that is the surface layer of the Earth. The crust is not a single, continuous piece. It is actually several different pieces, or plates, that come together to form the puzzle that comprises the surface of the Earth. These plates are in constant motion rubbing against one another. These areas, known as fault lines, where the plates rub up against one another have spots where one plate ”gets stuck while the rest of the plate keeps moving. When the plate has moved far enough, the edges unstick and is how most of the earthquakes around the world occur” (Wald, 2012). The energy stored from the friction of the two plate...
remains in highest regards among seismologists, engineers and geologists. It is said to be a
Psychology is the study of the mind and the behavior of mammals. Geology is a science that deals with the history of the earth and its life, recorded in rocks. The earth is consistently moving its tectonic plates. Therefore, there may be over 100 earthquakes a day; most of these earthquakes go unnoticed by humans on the crust of the earth. Other earthquakes for example, the one in 2011 located in Japan and the Loma Prieta earthquake of 1989 (Earth- Marshak). Unfortunately, many people died in horrific ways during these deadly earthquakes, leaving thousands diagnosed with psychological disorders such as, Posttraumatic Stress Disorder and Specific Phobias directly related to the natural environment of the earth.
The Tohoku earthquake caused by the movement of the Pacific plate slides underneath the Eurasia plate at the rate of three inches per year, associated with Japan Trench
More than a million earthquakes rattle the world each year. But, most are so small that they can only be detected by sensitive instruments called seismogram.
Earthquakes evidence themselves by shaking, trembling, and sometimes movement of the ground. They are caused by a slipper in the inner earthly faults. They can swing in capacity and in size, from the ones that are so weak that people don’t even feel, to those that can toss people around and can also destroy an entire city with its violent movement. Earthquakes by themselves unfrequently kill people. It is usually the secondary events, like buildings collapsing, tsunamis, fires, and volcanoes. Many of this type of things can be avoided by a better construction, early warning, and safety
It was a beautiful day like any other with the clear blue sky and the
Earthquakes belong to the class of most disastrous natural hazards. They result in unexpected and tremendous earth movements. These movements results from dissemination of an enormous amount of intense energy in form of seismic waves which are detected by use of seismograms. The impact of earthquakes leaves behind several landmarks including: destruction of property, extensive disruption of services like sewer and water lines, loss of life, and causes instability in both economic and social components of the affected nation (Webcache 2).