Name Learning Unit 4 Earthquake Review Questions This assignment is designed to assess your understanding of Unit 4 and includes some of the Questions for Review at the end of Chapters 3 and 4 from your text plus a few additional questions Each question can be answered in one to two sentences Please limit yourself to a maximum of three sentences Access the assignment complete it with ANSWERS IN A DIFFERENT COLOR FONT as a separate file and send it back for evaluation and grading through the assignment tab by or before the due date 1 What is meant by the elastic rebound theory Earthquakes are vibrations of the earth caused by the rupture and sudden movement of rocks that have been strained deformed beyond their elastic limit The forces that cause deformation and the build up of strain energy in the rock are referred to as stresses 2 What is the difference between the epicenter and the focus of an earthquake The focus is the point on the fault where rupture occurs and the location from which seismic waves are released The epicenter is the point on the earth s surface directly above the focus generally referenced by geographic location 3 Extension of the Earth s crust generally causes what type of fault or faults What type of plate boundary would produce such a fault or faults Normal Dip Slip Fault Divergent Boundary 4 Compression of the Earth s crust generally causes what type of fault or faults What type of plate boundary would produce such a fault or faults Reverse Dip Slip Fault Convergent Boundary 5 What is the motion of a P waves an S wave Surface waves P waves compress and extend the rock in the direction of wave travel S waves shear the rock perpendicular to the direction of wave travel Love waves create a complex horizontal motion Rayleigh waves create an elliptical rolling motion 6 Which type of earthquake waves do the most damage Surface waves 7 In what order do seismic waves arrive to distant locations Primary secondary surface or P S surface 8 How do seismologists determine how far away an earthquake was from their seismograph The lag time between the arrival of the first recorded P wave and first recorded S wave is proportional to distance traveled Therefore they determine the lag time between the P and S wave arrival and knowing the different velocities of those waves calculate the distance 9 How do seismologists determine the location of an earthquake epicenter They determine the distance of the earthquake from at least 3 seismographs of quite different locations and draw circles of distance from each seismograph The earthquake is at the intersection of the 3 distance circles 10 What does the Richter Magnitude Scale depend on Based on the highest amplitude wave measured on a seismogram corrected for distance from the seismograph to the epicenter 11 How much greater energy is released by a magnitude 6 earthquake than a magnitude 5 earthquake How much greater energy is released by a magnitude 7 earthquake than a magnitude 5 earthquake A magnitude 6 earthquake releases approximately 30 times more energy than a magnitude 5 32X more energy to be more precise A magnitude 7 earthquake releases approximately 900 times more energy calculated 30x30 than a magnitude 5 32x32 1024 times more energy to be precise 12 What are the three main factors that affect moment magnitude The rock strength area of rock broken and amount of offset across the fault 13 What does the Mercalli Intensity Scale depend on Based on people s reported perceptions of shaking subjective and the type and extent of damage produced objective 14 In addition to the amount of damage increases in what factors go along with an increase in earthquake magnitude fault offset length of fault ruptured acceleration of the ground time of shaking velocity of motion of the ground 15 Why are structures built on soft sand or mud often destroyed in an earthquake when nearby structures built on bedrock remain essentially undamaged Bedrock is resistant to shaking and therefore shakes with small amplitude vibrations Soft sediment amplifies shaking and therefore shakes with stronger large amplitude vibrations meaning greater back and forth distances which causes more damage 16 What is liquefaction Liquefaction is a quicksand like condition that occurs in water saturated soil and rock The shaking of earthquake waves causes the soil or rock to turn into a weak fluid like mass Structures built on areas that liquefy may fall over or sink 17 What kinds of structural materials make dangerously weak walls during an earthquake Bricks concrete blocks stone or adobe mud 18 What type of wall strengthening is commonly used to prevent a building from being pushed over laterally during an earthquake Diagonal braces or plywood sheeting built into the walls to keep the building from deforming during base shear 19 What can be done to a building either during construction or after to reduce the shaking of the building during an earthquake and therefore reduce the possibility of severe damage Use base isolation pads between the building and its foundation The base isolation pads act as shock absorbers to minimize transfer of ground shaking to the building 20 Freeway overpasses often collapse in a strong earthquake even though their supports are concrete and heavy duty steel reinforcing bars Why Shaking in the earthquake cracks and crumbles the concrete That leaves the rebar without lateral support so it bends and the freeway collapses 21 Why are building fires so hard to fight after an earthquake Broken water mains impassable roads 22 List several of the precursors that have been used to indicate that an earthquake may be coming Ground deformation Foreshocks Water Level in Wells Emission of Radon Gas Abnormal Animal Behavior 23 There has been at least one highly successful prediction of a major earthquake that saved a very large number of lives Where and when was that earthquake What information lead to the prediction Haicheng China in 1975 Foreshock activity bulging of the ground surface near the fault changes in groundwater levels and strange animal behavior led to the prediction 24 What is a seismic gap and what is its significance A seismic gap is a section of an active fault that has not had a recent earthquake The theory here is that if a portion of a fault has been locked for some time i e has not had an earthquake in a long time then strain may have built up to especially high levels there and a large quake may occur in the near future 25
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