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Chapter 6 Summary

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I have learnt that mostly faults do not move but whenever faults suddenly move, they producesearthquake. Earthquake occur due to the previous existing faults. Hypocenter is the place wheremovement occur and epicenter is the point above the hypocenter. Large earthquakes carry energyas seismic waves. Whenever faults move, energy transmit in all directions. Only 15 strongearthquakes are recorded while others are small. Volcanic eruption, landslide etc. causes smallearthquakes. Stresses accumulate slowly and when overcome frictional resistance then slippageoccurs and causes earthquake, this also shows elastic behavior or rock. Mountain buildingprocess along convergent boundaries causes faults. Transform fault boundaries consists of smallfractures and branches. Slippage occurs slowly. The study of earthquake is called seismology.Seismographs are used to measure earthquake and the record is called seismograms. The typesof earthquake from slippage is called body wave and other is called surface wave. Body wavesare primary and secondary waves. Surface waves are also of two types. First wave surface tomove up and down while other type causes surface to move side to side. Most of the earthquakeoccurs along circum-Pacific belt. Six major earthquake have occur in central and eastern US.Travel-time graphs are constructed by seismograms are used to determine location of earthquake.Intensity scales uses property damage to measure ground shaking, while magnitude scalesmeasure amount of energy. Modified Mercalli intensity scales have 12 points that shows differentdamages level and shows that building destroys at 10 point. Richter magnitude scale measureearthquake size by measure amplitude of largest seismic wave. Moment magnitude estimateamount of energy released during earthquake. Most violent earthquake has occurred in NorthAmerica of moment magnitude 9.2 that lasts for 3 to 4 minutes causes’ major loss to economy.Damage to human made structure depends upon intensity, duration, nature of material wherestructure is build and building material. Soft material amplifies earthquake. Liquefaction occurswhen sandy stream deposits acts life fluid and their strength decreases. Landslide causes byearthquake causes major damage to structures. Fire, tsunamis also causes damage to property andpeople. 3000 earthquakes occurs every year. P and S- waves can be used to examine earthinterior. Seismic waves do not travel straight and they reflect, refract, diffract and this behaviorswas used to study the layers of earth. Study have shown that earth crust is of two types. First oneis continental and other is oceanic. Oceanic crust is 7 km thick and denser than continental crustwhile continental crust is 40 km thick. More than 82 % volume of earth is in mantle. Core isdivided into inner and outer core. Outer core is liquid so S-Waves cannot pass through it whileinner core is solid and dense.Rocks deform at plate margins where tectonic forces causes deformation. Deformation can beelastic which is temporary deformation, can be ductile or brittle. At convergent boundaries, flatrocks bend and form folds. Folds can be anticline that occur due to up-folding and can besyncline those are down-folds. Folds form different structure like dome and basin. Brittle rockscauses faults that move and faults can be dip-slip, normal, reverse and thrust, strike-slip. Whenthere occur no movement along fracture then it is called joint. The process by which mountainbelt is known as orogenesis. The driving force of orogenesis is subduction of oceanic lithosphere.I have studied different types of mountain form from subduction like Island Arc, Andean, SierraNevada and Coast Ranges. When buoyant crust fragments are collide with continental marginthen mountain belts are generated. Different mountain belts have generated like Cordilleran,Accretion and Orogenesis. I have also studied about Alpine type mountain building, Himalayas,Appalachians.I have studied that earthquake causes destructions that is a big loss to economy. But if energyreleased by earthquake could be control and stored then it can be used for useful purposes. Byusing that energy we can overcome our energy crises. In this way we can save our fuel and whenfuel will not use then our environment would be safe and we can enjoy our life happily.I have a question you guys that what steps should be taken to control earthquake and to storeenergy released by


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