Free Essays on Earthquakes

Earthquakes I. Seismic Waves to Study Earth’s Interior A. Travel Time, Reflection, Refraction of P & S Waves 1. Travel time of body waves gives us VP, VS, and (density) as a function of depth. 2. Velocity of P & S waves increases with depth. B. Earth’s Layered Composition 1. Crust a. Quartz, feldspar, and basalt. b. Continental Crust Mostly quartz and feldspar. Lower density than oceanic crust. Variable thickness (10-50 km). c. Oceanic Crust Mostly basalt. Higher density than continental crust. Uniform thickness (10 km). d. Isostacy Crust floats in equilibrium on the denser mantle beneath. 2. Mantle a. Ultramafic Rocks Olivine. Pyroxene. b. Low velocity zone: Convection in mantle distributes heat evenly. c. Polymorphic phase transition 400 km and 660 km. Pressure changes the crystal structure of minerals causing a slow in seismic wave velocity. 3. Core a. Core-Mantle boundary 2913 km. b. Nickel and FE. c. Inner core is 6271 km deep. d. Outer core boundary is 2900 km deep. e. Liquid outer core TM: Melting temperature of ultramafic rocks. S waves cannot propagate through the outer core (liquid). Iron, oxygen, and silicon. C. Mantle is mostly olivine. 1. Seismic waves a. VS, VP, and measured in lab match seismic measurements. 2. Zenolith a. Mantle rocks found in volcanoes with deep roots contain olivine. b. Kimberlite Volcanoes Mantle material brought up very quickly contains olivine and diamonds. Do not erupt anymore. 3. Ophiolite Suite a. Oceanic crest that’s been abducted onto continental crust contains olivine and the moho. 4. Primitive meteorites a. Examining carboneous chondrites (primitive meteorites) with olivine. D. Iron Catastrophy 1. This is how the earth became layered. 2. 4.3 billion years ago. II. Interpreting Seismograms A. Seismograms 1. Short period instruments: T 1 second (body waves).... Free Essays on Earthquakes Free Essays on Earthquakes Earthquakes Throughout history, man has made many advancements. These advancements have been made to make life easier. The one thing man can't do is to control Mother Nature. Mother Nature can cause many things such as earthquakes. The causes of earthquakes have been theorized in many ways. According to the book Predicting Earthquakes by Gregory Vogt, the Greeks, "blamed the earthquakes on Poseidon, god of the sea"(25). The Hindu believed that "the earth was a platform that rested on the back of eight great elephants. When one of the elephants grew weary, it lowered and shook its head causing the ground above to tremble"(Vogt 25). Margaret Poynter writes "many primitive people thought that the earth rested upon the back of some sort of animal. When that animal became restless, great cracks appeared in the ground, and tall trees swayed and fell. In South America, the animal was a whale. In Japan, it was a great black spider or giant catfish. One ancient tribe thought that four bulls supported the earth on their horns. To amuse themselves, they sometimes tossed it from one to another"(6). In the same book, Poynter says "The Chinese believed that monsters lived in the caves inside the earth. When the creatures fought, the surface of the earth trembled (6)." "In Greece, it was not an animal, but a titan named Atlas who was condemned to support the world upon his shoulders. Later, about the third century B.C., a Greek philosopher, Aristotle, had a more scientific explanation. He thought that earthquakes occurred only when hot air masses tried to escape from the center of the earth. Two centuries later, Lucretius, a Roman, wrote that underground landslides caused the earth's surface to move"(Poynter 7).2 Last Name Today, scientists have found a more logical reason to earthquakes. Scientists say almost 600 million years ago, all the continents were connected to form a huge super continent c... Free Essays on Earthquakes Until the 18th century, earthquakes were thought to be caused by air rushing out of caverns deep in the Earth's interior (Watson). But we all know that is not how an earthquake happens. The earth’s surface is broken into seven large plates (â€Å"Major plates in the world†). There are also many other little plates on the surface but seven main ones. Each one of these plates is approximately 50 miles thick and moves against each other a few inches a year (USGS). The seven main plates in the world are: Eurasian plate, Pacific plate, North American plate, Nazca plate, South American plate, Australian plate, and Antarctic plate (Major plates in the world). When the plates move against each other, it’s not just your average plate rubbing. There are three different types of movements at the boundaries of the plates: convergent, divergent and transform-fault (â€Å"Major plates in the world†). A convergent movement is when plates move tword each other and colide. An example is when an oceanic plate collides with a continental plate. The oceanic plate slides under the continental plate making a huge ocean trench. This is called a subduction and you can find it where the Nazca plate and the continental Sout American plate (â€Å"Major plates in the world†). When continental plates collide, they form new major mountain systems such as the Himalyans (Watson). A divergent movement is when plates move away from each other. The mid-Atlantic ridge is from a divergent movement (â€Å"Major plates int the world†). When plates diverge, hot molten rock rises, cools, and fills in the emty spaces adding new formation to the edges of the oceanic plates (Watson). This is also known as sea-floor spreading. (â€Å"Major plates in the world†). A transform movement is when two plates move horizontal on each other A perfect example of this is the San Andreas fault (â⠂¬Å"Major plates in the world†). Los Angelas lies on the Pacific plate and is slowly moving... Free Essays on Earthquakes Earthquakes I. Seismic Waves to Study Earth’s Interior A. Travel Time, Reflection, Refraction of P & S Waves 1. Travel time of body waves gives us VP, VS, and (density) as a function of depth. 2. Velocity of P & S waves increases with depth. B. Earth’s Layered Composition 1. Crust a. Quartz, feldspar, and basalt. b. Continental Crust Mostly quartz and feldspar. Lower density than oceanic crust. Variable thickness (10-50 km). c. Oceanic Crust Mostly basalt. Higher density than continental crust. Uniform thickness (10 km). d. Isostacy Crust floats in equilibrium on the denser mantle beneath. 2. Mantle a. Ultramafic Rocks Olivine. Pyroxene. b. Low velocity zone: Convection in mantle distributes heat evenly. c. Polymorphic phase transition 400 km and 660 km. Pressure changes the crystal structure of minerals causing a slow in seismic wave velocity. 3. Core a. Core-Mantle boundary 2913 km. b. Nickel and FE. c. Inner core is 6271 km deep. d. Outer core boundary is 2900 km deep. e. Liquid outer core TM: Melting temperature of ultramafic rocks. S waves cannot propagate through the outer core (liquid). Iron, oxygen, and silicon. C. Mantle is mostly olivine. 1. Seismic waves a. VS, VP, and measured in lab match seismic measurements. 2. Zenolith a. Mantle rocks found in volcanoes with deep roots contain olivine. b. Kimberlite Volcanoes Mantle material brought up very quickly contains olivine and diamonds. Do not erupt anymore. 3. Ophiolite Suite a. Oceanic crest that’s been abducted onto continental crust contains olivine and the moho. 4. Primitive meteorites a. Examining carboneous chondrites (primitive meteorites) with olivine. D. Iron Catastrophy 1. This is how the earth became layered. 2. 4.3 billion years ago. II. Interpreting Seismograms A. Seismograms 1. Short period instruments: T 1 second (body waves).... Free Essays on Earthquakes Earthquakes Earthquakes have plagued our lives for as long as people have inhabited the earth. These dangerous acts of the earth have been the cause of many deaths in the past century. So what can be done about these violent eruptions that take place nearly with out warning? Predicting an earthquake until now has almost been technologically impossible. With improvements in technology, lives have been saved and many more will. All that remains is to research what takes place before, during, and after an earthquake. This has been done for years to the point now that a successful earthquake prediction was made and was accurate. This paper will discuss a little about earthquakes in general and then about how predictions are made. Earthquake, â€Å"vibrations produced in the earth's crust when rocks in which elastic strain has been building up suddenly rupture, and then rebound.†(Associated Press 1993) The vibrations can range from barely noticeable to catastrophically destructive. Six kinds o f shock waves are generated in the process. Two are classified as body waves-that is, they travel through the earth's interior-and the other four are surface waves. The waves are further differentiated by the kinds of motions they impart to rock particles. Primary or compressional waves (P waves) send particles oscillating back and forth in the same direction as the waves are traveling, whereas secondary or transverse shear waves (S waves) impart vibrations perpendicular to their direction of travel. P waves always travel at higher velocities than S waves, so whenever an earthquake occurs, P waves are the first to arrive and to be recorded at geophysical research stations worldwide.(Associated Press 1993) Earthquake waves were observed in this and other ways for centuries, but more scientific theories as to the causes of quakes were not proposed until modern times. One such concept was advanced in 1859 by the Irish engineer Rob...