EARTHQUAKE
Introduction:-
1 Definition:
An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Figure 1; Showing the fault plane, point of origination and epicenter
(http://earthquake.usgs.gov/learn/kids/eqscience.php)
2 Earthquake Geophysics:
The earth has the following structure, a 30 km thick crust, a 2900 km thick mantle, and a radius of 3470 km core, which forms the total radius 6370 km. The crust mantle and core are further divided in to subtypes like core is divided in to outer core and inner core. There is elasticity present in the earth’s crust and it produces strain when it under goes some stresses. Elastic rebound theory of Reid is based on this property.
Reid suggests that ‘the crust, in many parts of the earth, is being slowly displaced, and the difference between displacements in neighboring regions sets up elastic strains, which may become greater than the rock can endure. A rupture then takes place, and the strained rock rebounds under its own elastic stresses, until the strain is largely or wholly relieved’.
The point where the earthquake is originated is called focus or hypocenter and on the earth surface directly above the focus, the point is called epicenter. Earthquakes are divided in to the following types according to their depths
1) Shallow focus (focus depth < 70 km)
2) Intermediate focus (depth 70-300 km)
3) Deep focus (depth > 300km)
Wave’s passes through earth and produce motion to the ground during an earthquake. There a...
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...akes.
7.4 Results:
The moment magnitude of KME was the smallest from the all the four earthquakes but the range of groundwater level change is highest from all the four earthquakes from -0.2m to 0.67m among the 54 wells. The short distance of study area to the hypocenter can be the reason for the big range of change. FOE had hypocenter which was located at shortest distance to the study area at the second number and this earthquake had also second strongest effect. Hypocenter for GYE was far from study area and thus it also had less effect on the water level, same case for the SCE earthquake its hypocenter was located 2500 Km from the study area.
The range of ground water level changes due to FOE earthquake was 0.01m – 0.15m which was at second number. The range of water level change for GYE earthquake was 0.01m – 0.05m while for SCE earthquake was 0.01m – 0.04m.
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...
Paterson, S., and Tobisch, O. (1992). Rates of processes in magmatic arcs: implications for the timing and nature of pluton emplacement and wall rock deformation. Journal of Structural Geology. 14 (3), p291-300.
Yan, F., Feng, X., Chen, R., Xia K., Jin, C., Dynamic Tensile Failure of the Rock Interface
The science of the natural disaster has baffled many, but from studying the San Francisco earthquake, scientists have made a number of important discoveries and they have a better understanding of earthquakes. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared 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”). The shearing caused a loud rumble in the Californian city of San Francisco. 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”). Moreover, the earthquake could be recorded on a seismograph in Capetown, South Africa, an astounding 10,236 miles away from San Francisco (“San Francisco ea...
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...
Since California had previously been mentioned, it is a great place to begin explaining the complex geological impacts starting with the San Andreas Fault. The San Andreas is what geologists know as a strike-slip fault, meaning that when two pl...
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...
The earthquake was caused by a strike-slip fault. A strike-slip fault is when the rupture is almost nearly vertical movement. During an earthquake, they slide past each other.
Understanding the plate tectonics theory is very important, especially when investigating natural disasters like earthquakes, and volcanic eruptions. It is also gives scientists the ability to understand how mountains were formed between two tectonic plates. There are three types of interactions between plate boundaries: convergent, divergent and transform. Looking back at the history of these three different interactions, earthquakes, like the one in Haiti, volcanic eruptions, like at Mount St. Helens, and the creation of mountain belts, like the Mid-Atlantic Oceanic ridge, gives information on future consequences of tectonic movement, and what can happen when the plates interact with each other.
The epicenter of the earthquake in Alaska was about 10km east of the College Fiord, approximately 90km west of Valdez and 120km east of Anchorage, Alaska largest city. The earthquake was felt about 1,300,000 square kilometers away from the epicenter. (Christensen, Doug PhD.) About 30 kilometers deep, the first slip occurred under northern Prince William Sound, and an 800 kilometer rupture in the rocks extended horizontally, roughly parallel to the Aleutian trench. (Bolt) The cause of this massive earthquake was the vertical displacement of northwest motion of the Pacific plate. Also, it was estimated that about 200,000 square kilometers of the crust were deformed, making this the greatest area of vertical displacement ever measured. (Bolt)
They are the earth’s crust; they move very slowly every year. As the tectonic plates slide over each other they cause earthquakes. Earthquakes produce various damaging effects this includes damage to structures of buildings, bridges and other standing formations which then...
The Pacific plate is moving northwest in relation to the North American plate, and it is believed that the total displacement along the fault since its formation more than 30 million years ago has been about 350 mi. Movement along the fault causes earthquakes; several thousand occur annually
Due to the fact that rocks are composed of high intensity of elastic and brittle material, they therefore store considerable amount of strain energy that results from elasticity, during the action of plate tectonic. The brittleness leads to development of concurrent cracks on the rocks as a result of plate’s action.