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GEOL 240 Fall - 2005 Midterm 2

GEOL 240 Fall - 2005 Midterm 2 - GE 240 Midterm 11 Fall...

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Unformatted text preview: GE 240 Midterm 11 Fall 2005 Earthquakes Blue Dr. Sammis Part I : TRUE-FALSE Mark the AT or F column on your Scantron sheet. & l) Teleseismic surface waves generally have a longer period than teleseismic body waves. 2) In general, an earthquake’s Mercalli intensity decreases with distance from the epicenter. 3) If a magnitude 5 earthquake produces an amplitude of 10 mm of ground motion, a magnitude 3 earthquake at the same distance will produce about 2.5 mm of ground motion. 4) T An S wave is best recorded on a short-period vertical instrument. {Ln mf [ 5) The magnitude of an earthquake decreases with distance. 6) Isostacy explains why continental crust is usually at a higher elevation than oceanic crust. 7) Rayleigh waves are only recorded on a vertical seismograph. 8) Love waves are never recorded on a vertical seismograph. 9) S waves do not propagate in the inner core. I I) The moho marks the base of the Lithosphere. [2) The rocks below the moho have a higher density than those above. 13) An earthquake may be located using only the P arrival time at 3 stations. 14) The seismic discontinuity at 400 km is probably due to a change in the composition of the rocks. 15) Earthquakes larger than Mb=8.9 have never been recorded because of the lack of a proper seismograph. 16) Almost all earthquakes larger than Mb: 6.0 are preceded by at least one foreshock. 17) Typical continental rocks are composed of basalt. 18) For every magnitude 4 earthquake in an aftershock sequence there are roughly 1000 magnitude 1 earthquakes. T R ‘F F F T F T F. ‘T‘ 10) Snell's law applies equally well to reflected and refracted waves. F T f F F f l; ‘ T F 19) The seismic low—velocity-zone is a liquid layer between 100 and 200 km depth where temperatures in the mantle are at the melting temperature of the ultramafic rocks. T 20) We know that the outer core is liquid because it does not transmit S waves. T 2!) Rocks in the upper mantle between 100 and 200 km depth are closer to their melting temperature than rocks which occur in the lower mantle between 2000 and 2400 km. T 22) Most large (Mb>6.0) earthquakes have at least one aftershock that is one magnitude less than the .T- mainshock. . 23) The earth's upper mantle is composed largely of the mineral olivine. a r 24) The maximum Mercalli intensity always occurs at the epicenter. f 25) Each earthquake is assigned one intensity between I and X11 on the Modified Mercalli intensity scale. Part II : MULTIPLE CHOICE Mark the best choice on your Scantron sheet 200 400 600 Depth (km) On the diagram above, identify the following features: 26) The crust E) 27) the aesthenosphere lb D 28) a polymophic phase boundary E 29) the moho P\ 30) the lithosphere Q 31) the seismic low—velocity-zone D Answer the next 5 questions based on the diagram below. Earthquake ~ - E Which ray path corresponds to the following phases? 32) PS E 33) PKP KB 34) PKIKP C/ 35) Which phase on the diagram proves that the inner core is solid? 9 36) The S wave recorded at station E is 3% A) SH C) A surface wave. B) SV D) SS 5%»! AH'H' . . . R 37) Snell’s law is fl=sm V1 V2 variables in this equation? IR . Which of the below diagrams correctly depicts the A} Answer the next 7 questions from the choices below A) Continental crust C) Mantle E) Inner core B) Oceanic crust D) Outer core 38) This isaliquid layer :P /E \\ 39) This is a solid Fe, Ni, S layer. E \Kiy' 40) The highest temperature in the Earth’s interior occurs here. -E 41) This layer contains the seismic low-velocity-zone. C, 42) The upper boundary of this layer is the moho C/ 43) This layer has a basaltic composition. 9 44) This layer has the lowest average density of all the layers listed above. “Pl Answer the next 5 questions using the choices below: a) long-period vertical c) long-period horizontal b) short-period vertical (1) short-period horizontal Which of the above seismographs is best used to measure the arrival time of the following seismic waves from a teleseismic event? 45) P wave a 46) SV wave 0 47) SH wave ,0 48) Love wave 0 49) Rayleigh wave f\ The ray diagram above shows an S wave incident on a boundary between two solid layers (layer l above and layer 2 below). Which letter labels the : 50) reflected F wave } 51) reflected S wave fl 52) refracted P wave C 53) refracted 5 wave y 54) The S waves in this case are A) SH C) SV and SH @sv D) SP 55) Based on the ray diagram above, which of the following is gm? A) Vs,>VP, © Vs,>'v'51 B) V52>Vsr D) ‘15?sz Answer the next 4 questions based on the diagram below O = First P up 0 = First P down 56) This diagram represents A) normal faulting D) right—lateral strike—slip faulting B) reverse faulting @C or D C) left—lateral strike-slip faulting 57) Which seismic station was closest to the earthquake? A) A B) B C) C @3 58) The orientation of 01 for this faulting is approximately A) N—S @E—W C) NE—SW D) NW-SE E) vertical 59) The orientation of 03 for this faulting is approximately CNS B) E-W C) NE—SW D) NW-SE E) vertical UP '1—~—I> «4—03 On the diagram above, identify the following arrivals: 60) direct Pwave A f. /7r‘\ 61) direct S wave 6, \J 62) Rayleigh wave B 63) Love wave 9 64) The first horizontal motion of the Rayleigh wave is most nearly A) NE C) N @S E) SW D) E 65) The first vertical motion of the Rayleigh wave is A) S C) N B) UP @DOWN 66) Hence, this earthquake lies 9 of the station. A) NE ©N E) s B) sw D) E E) NE Travel I: Time B A 100 200 300 Distance (km) 67) The above graph is called A) a time—distance curve @a travel-time curve B) none of the above B) a seismograph D) a ray diagram Which branch above corresponds to the 68) direct 5 wave 9 69) direct P wave A 70) the Rayleigh wave _0 71) the Love wave 0 72) Branch E corresponds to the A) SKS wave @CS wave E) none of the above B) PCP wave D) SS wave ...
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