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Understanding Earthquakes By: Brooke Delucci, Courtney Stamps, Maria Johnson, Jordan Anglin What are Seismic Waves Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs. (Japan Earthquake)-> Seismic Waves Not all waves are created equal! You need to be able to see the specific “faces” that each wave can have, based on three important characteristics: frequency, wavelength, and amplitude. Frequency is a measurement of how many cycles can happen in a certain amount of time… cycles per second. Wavelength is defined as the distance from a particular height on the wave to the next spot on the wave where it is at the same height and going in the same direction. Amplitude is a measure of how big the wave is. Defining Waves Amplitude (energy of the wave) Wavelengths (length of the waves) Defining Waves Transverse Waves Transverse waves are the waves that have the classical wave shape everyone thinks of when they imagine a wave. Particles of the medium move perpendicular to the direction the transverse wave itself is moving. Different Seismic Waves The are many different seismic waves, but all of basically of four types: 1. Compressional or P (for primary) 2. Transverse or S (for secondary) 3. Love 4. Rayleigh Body waves travel through the interior of the Earth. They create ray paths refracted by the varying density and modulus (stiffness) of the Earth's interior. The density and modulus, in turn, vary according to temperature, composition, and phase. Surface waves are analogous to water waves and travel along the Earth's surface. They travel slower than body waves. Because of their low frequency, long duration, and large amplitude, they can be the most destructive type of seismic wave. They are called surface waves because they diminish as they get further from the surface. Compressional Waves (P waves) • P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the ‘direction of wave propagation’. • This is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. • Usually people can only feel the bump and rattle of these waves. • http://www.geo.mtu.edu/UPSeis/images/Pwave_animation.gif Transverse Waves (S waves) This is the second wave you feel in an earthquake. An S wave is slower than a P wave. S waves move rock particles up and down, or side-toside--perpendicular to the direction that the wave is traveling in (the direction of wave propagation). Transverse waves are always characterized by particle motion being perpendicular to wave motion. http://www.geo.mtu.edu/UPSeis/images/Swave_animation.gif Love Waves The first kind of surface wave is called a Love wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side. Confined to the surface of the crust, Love waves produce entirely horizontal motion. http://www.geo.mtu.edu/UPSeis/images/Love_animat ion.gif Rayleigh Waves Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Rayleigh waves are the slowest of all the seismic wave types. As a Rayleigh wave passes, a particle moves in an elliptical trajectory that is counterclockwise. http://www.geo.mtu.edu/UPSeis/images/Rayleigh_animation.gif When the earth quakes… • Every earthquake sends out an array of seismic waves in all directions. • Recordings of seismic waves from earthquakes gave us the first clues about the earth’s composition. When traveling through the earth, seismic waves frequently pass through materials that alter the speed of the waves. Earths Structure: Crust • Two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. • Each type is made up of different types of rock causing the waves to travel in various paths and speeds depending on the material they are passing through. • Oceanic crust is composed mostly of basalt which is a sedimentary rock allowing waves to travel easily resulting more destruction on the surface. • Continental crust is mostly granite, a igneous rock type, which is of a much lower density allowing it to “float” on the deeper layer of higher density material called the mantle • From about 10 to 200 km is the lithosphere region of the crust which is formed of lithosphere plates that are floating on the mantle. Discontinuity Boundary • There is a distinct difference between the outer shell of the earth and the denser mantle, the surface between the two is known as the Mohorvicic Discontinuity or Moho. • The Moho was detected by a sharp increase downward in the speed of waves at a certain depth. • The observations were made during a 1909 earthquake. • This is considered to be the lower boundary of the crust. The Mantle Within the mantle there is a steady increase of temperature as depth increases known as the geothermal gradient. This gradient is responsible for the different rock behaviors which form the boundaries between the upper mantel and the lower mantle. The materials in the mantle are aluminum, silicon, iron, magnesium, and oxygen. These rocks and minerals are all of the denser materials called peridotite. Upper Mantle: Comprised of a temperature cool enough to causing rocks to be brittle enough to break under stress and produce earthquakes. As the rocks break energy is produced causing waves to distribute in all directions. Mantle Continued Lower Mantle: Has a much higher heat level causing the rocks to be soft and flow when subject to stress instead of breaking. Although soft, the rock here is not yet molten causing it to be plastic like. This part of the earth is also referred to as the asthenosphere which is partially molten material that flows but is not a liquid. The Core The core is earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances. S waves inability to travel through the core suggests that at least the outer core is a liquid. The temperatures here are adequate to melt the iron-nickel alloy making up the Earth’s core . The inner core is a solid even though its temperature is higher than the outer core. Tremendous pressure produced by the weight of the overlying rocks forces the atoms to be so tightly packed that a liquid state cannot occur. At 660 km Mesosphere begins where the pressure become so great that the material can no longer flow. How waves react in the earth When seismic waves hit a surface (boundary) between very different materials they may bounce off this surface causing reflections, refractions, and scattering of the wave paths. Reflection A seismic reflection occurs when a wave impinges on a change in rock type (which usually is accompanied by a change in seismic wave speed). Part of the energy carried by the incident wave is transmitted through the material and part is reflected back into the medium that contained the incident wave. In seismology, reflections are used to prospect for petroleum and investigate Earth's internal structure. The amplitude of the reflection depends strongly on the angle that the incidence wave makes with the boundary and the contrast in material properties across the boundary Refraction Refraction: When seismic waves pass through different types of materials their speed is altered and consequently their path through the materials may be bent causing refraction. Refraction may occur at a distinct boundary like reflection, but it also occurs when the material changes slowly. All paths through the earth tend to bend upward. This is a result of refraction because materials deeper in the earth conduct seismic waves faster than materials above. When a seismic wave hits any interface, there can be reflection, refraction, scattering, or it can stop completely. Scattering Scattering is a general physical process where waves are forced to deviate from a straight trajectory because of a nonuniform medium that it must pass through. Reflections that undergo scattering are often called diffused reflections because the waves disperse in all directions. Epicenter The epicenter of an earthquake is the point on the Earth's surface directly above the underground area where the rock breaks which is called the focus of the earthquake. The intensity of ground shaking depends on distance from the epicenter and on the type of bedrock underlying the area. In general, loose unconsolidated sediment is subject to more intense shaking than solid bedrock When an Earthquake occurs, seismic waves are emitted from the focus (=hypocenter) there are several paths that it can take through the earth before emerging again at the surface. Plate Tectonics All plates are moving in different directions at different speeds. 2 to 10 centimeters per year about the speed that fingernails grow. The place where two plates meet is called a plate boundary. The name of the boundary depends on the way they move in relation to each other. 3 Types of Movement Convergent Boundaries: crashing Divergent Boundaries: pulling apart Transform Boundaries: sideswiping Cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon. Convergent Boundaries Two plates moving toward each other. A very slow “collision.” Sometimes the plate sinks under another causing a subduction zone. The subducting plate breaks into smaller pieces that become locked in place before suddenly moving to generate large earthquakes. The South American Plate is being lifted up creating the Andes mountains. Types of Convergence -Trenches, volcanic arc, and mountains -Island volcanic arcs and trenches -Mountain ranges Divergent Boundaries Two plates are moving apart. New crust is created by magma pushing up from the mantle. The pulling apart causes a rift in the plates and can cause volcanoes to form mostly underwater. Mid-Atlantic Ridge in Iceland. Transform Boundaries The zone between two plates sliding horizontally past each other. They are sometimes marked by linear valleys were rock has been ground up by sliding. Most are found on the ocean floor. The most famous land one is the San Andreas Fault zone in California. San Andreas Fault 1,300 km long Cuts through 2/3 of California. The west slice is slowly moving north. The sliding causes several earthquakes. What is Fracking? The process of drilling down and creating tiny explosions to shatter and crack hard shale rocks to release the gas inside. Water, sand and chemicals are injected into the rock at high pressure which allows the gas to flow out to the head of the well. Why is Fracking Such a Big Deal? Most of the water used for fracking is collected from a well and processed. However, there are some concerns that chemicals can escape sometimes and find their way into our drinking water. The other big concern with fracking is that it causes small Earth tremors. Does Fracking Cause Earthquakes? http://www.youtube.com/watch?v=3GPWZfNHeNM Where is the New Madrid Fault? The New Madrid Fault system extends 120 miles southward from the area of Charleston, Missouri, and Cairo, Illinois, through New Madrid and Caruthersville, following Interstate 55 to Blytheville and on down to Marked Tree, Arkansas. It crosses five state lines and cuts across the Mississippi River in three places and the Ohio River in two places. Major Concerns with the New Madrid Fault Many are concerned that with recent earthquakes around the world that they have caused the New Madrid plates to shift. 2nd highest risk area in the United States for an earthquake. 3% chance of another major earthquake in the area in the year 2040. Earthquakes In Arkansas December 16, 1811 – 7.7 magnitude earthquake in northeast Arkansas with a 7.0 magnitude aftershock earthquake that followed. January 5, 1843 – 6.3 magnitude earthquake in northeast Arkansas. April 30, 2003 – 4.0 magnitude earthquake in Blytheville. February 10, 2005 – 4.1 magnitude earthquake in northeast Arkansas. May 1, 2005 – 4.2 magnitude earthquake in northeast Arkansas. February 28, 2011 – 4.7 magnitude earthquake in central Arkansas. Last Earthquake In Arkansas There are small earthquakes in Arkansas almost every day. Many are attributing them to fracking. The last one recorded was on June 15, 2012 at 1:23 pm. It was a 2.2 magnitude earthquake so more than likely they are not felt. What To Do In An Earthquake Get in a doorway. If you can’t get in a doorway get under a desk or a large piece of furniture. Don’t go down a stairway because the stairs may collapse. http://www.youtube.com/ watch?v=I2eqRYxOef0 References http://www.bbc.co.uk/news/uk-14432401 http://8020vision.com/2011/04/17/congress-releases-report-on-toxic-chemicals-used-in-fracking/ http://www.treehugger.com/culture/burning-tap-water-and-more-gasland-exposes-the-natural-gas-industry.html http://www.youtube.com/watch?v=3GPWZfNHeNM http://earthquake.usgs.gov/earthquakes/states/arkansas/hazards.php http://earthquake.usgs.gov/earthquakes/states/historical_state.php http://earthquake.usgs.gov/earthquakes/eqarchives/last_event/states/states_arkansas.php http://www.youtube.com/watch?v=I2eqRYxOef0 http://room1halcombeschool2012.blogspot.com/2012/02/earthquake-practice.html http://activerain.com/blogsview/2562810/the-california-shakeout-2011-biggest-earthquake-drill-in-history http://www.scchealth.org/docs/ems/docs/prepare/newmadrid.html http://www.studyphysics.ca/newnotes/20/unit03_mechanicalwaves/chp141516_waves/lesson44.htm http://boingboing.net/2011/03/14/geologist-explains-s.html http://en.wikipedia.org/wiki/Seismic_wave http://www.geo.mtu.edu/UPSeis/waves.html http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif http://www.physicsclassroom.com/class/waves/u10l1c.cfm http://www.geo.mtu.edu/UPSeis/images/Love_animation.gif http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html http://www.studyphysics.ca/newnotes/20/unit03_mechanicalwaves/chp141516_waves/lesson43.htm References http://pubs.usgs.gov/gip/dynamic/understanding.html http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html http://www.physicalgeography.net/fundamentals/10h.html http://search.babylon.com/imageres.php?iu=http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT407/IMAG ES/AACHCOV0.JPG&ir=hrc=NT_ss Krauskopf, Konrad. (2010). The Physical Universe. New York:The Mcgraw Hill Companies p. 551-560, 573-581. http://faculty.weber.edu/bdattilo/shknbk/notes/insdearth.htm http://www.visionlearning.com/library/module_viewer.php?mid=69 http://www.iris.washington.edu/edu/onepagers/no2.pdf https://etap.org/demo/Earth_Science/es3/iinstructions5tutor.htm http://crackseismo..urr.edu/ftp/pub/louie/class/100/interior.html