GLY1000 Exam 2 Terms Notes Concepts Earthquakes CH 10 Stress force applied to rocks Rocks release stress through motion if possible If friction prevents this motion deformation occurs Pressure is a form of stress There is tensional compressional shear stresses depending on direction Strain is a change in size shape or volume of a material Elastic strain is reversible measure of an objects ability to change shape when a force is applied to it and return to its original shape when the force on it is released Elastic limit is determined by Temperature higher becomes plastic Pressure greater confining pressure from all directions becomes plastic Time slower stress is applied becomes plastic Plastic plastic means that the shape of an object can be changed an additional amount beyond its elastic limit before it breaks other times if the substance is brittle it breaks at its elastic limit before any plastic deformation occurs There is also elastic rebound in which objects return to their original shape After they have been broken apart During an earthquake seismic waves are generated as a result of this type of rebound Deformation process where rocks are folded faulted sheared or compressed by Earth stresses Temperature pressure time leads to rock deformation See above S wave shear secondary These are body waves As an s wave propagates it shears the the rock sideways at right angles to the direction of travel S waves will not travel through liquid Much slower than P waves P wave primary pressure these are body waves Their motion is the same as that of a sound wave in that as it spreads out it alternately pushes compresses and pulls the rock These p waves are able to travel through both solid rock such as granite and liquid or flowing material such as volcanic magma the distance between the p wave and the s wave on a seismograph determines how close to the epicenter the reading took place this was a clicker question the shorter the distance the closer to the epicenter the reading took place Body wave a wave that travels beneath the surface of the earth Surface wave a wave that travels through the surface of the earth Shear shearing is something that happens when two plates from transform boundaries slide past each other Focus or hypocenter the place within the Earth where rock ruptures and slips causing earthquake waves This occurs underground Epicenter the point on the surface of the earth directly above the focus hypocenter geologists represent epicenters as dots on maps dot size indicate magnitude of the earthquake Seismograph A seismograph or seismometer is an instrument used to detect and record earthquakes Richter American seismologist who developed a method for defining and measuring earthquake magnitude which came to be known as the Richter Scale On the Richter Scale magnitude is expressed in whole numbers and decimal fractions For example a magnitude 5 3 might be computed for a moderate earthquake and a strong earthquake might be rated as magnitude 6 3 Richter magnitudes are based on the maximum wave amplitude Each step in the Richter scale is 10X the previous step The amount of energy released increases approx 30X for each step Amplitude the size of the wiggles on an earthquake recording more precisely it is the size of a wave from crest to trough Magnitude a number that indicates the side if an earthquake at a specified distance from the epicenter determined by measuring the maximum amplitude of ground motion recorded by a seismograph Use of a magnitude scale allows seismologists to define the size of an earthquake in a uniform way Energy seismologists can calculates the energy release of an earthquake from equations that relate magnitude to energy According to some researchers a magnitude 6 earthquake releases about as much energy as the atomic bomb Lag time aforementioned gap between p wave and s wave Mercalli system to define intensity of an earthquake by systematically assessing the damage that occurred The modified Mercali Scale uses roman numerals from I extremely low to XII extremely high Whereas Richter scale is based on mathematics the Mercalli Scale is a subjective assessment of perception and damage not on a direct measurement with an instrument Intensity refers to the effect or consequence of an earthquake s ground shaking at a locality on the Earth s surface Building failure Most buildings are designed to support their own weight vertical loads Some attention is paid to lateral loads like the wind but building design typically focuses on vertical loading Depending on the direction of the slip during an earthquake a building can experience too much lateral or vertical stress resulting in structural damage or at its worst failure However it is usually too much lateral load that causes the most damage Masonry consists of un reinforced brick or cement and mortar An earthquake will Push and Pull on the bricks and so it causes the bricks to crack Steel frame more flexible and less easy to break however if under enough pressure steel reinforcement can warp or even worse melt with a hot enough temperature Wood more flexible than concrete however it can snap if under enough pressure and can catch fire much more easily than steel Substrate Housing in very populated areas can be hard to find so builders begin to build on compacted trash landfill material However this material is not very reliable as a foundation and can break down when hit or shaken by a seismic wave As a result housing fails and often slides off the foundation sometimes into water Resonance happens when each new earthquake wave arrives at just the right time to add more energy to an earthquake system Fires the shaking during an earthquake can make lamps stoves or candles with open flames tip over and it may break wires or topple power lines generating sparks As a consequence areas may be consumed by fire This is especially dangerous to buildings with wooden structures Disease earthquakes cut water and sewer lines destroying clean water supplies and exposing the public to bacteria They also damage routes and modes of transportation preventing food and medical supplies from reaching the area Cholera is a risk Exposure when homes are destroyed those who lived in them are forced to live elsewhere often victim to exposure to the elements and disease Liquefaction A process by which water saturated sediment temporarily loses strength and acts as a fluid like when you wiggle your toes in the wet sand near the
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