Solved: Visualizing ConceptsIdentify each of the following

Modified Mercalli Scale III. Felt indoors V. Felt Outdoors VI. Objects fall, furniture overturned VII. Difficult to Stand VIII. Difficult to steer a car XI. Rails bent greatly Modified Mercalli Scale *Data from the 1989 Loma Prieta, CA (“world Series”)earthquakes: larger Roman Numerals= greater intensity/destruction Area of Effect vs. Thermal Structure of Crust *The area affected by a large earthquake depends in part on the rocks involved: cold, thick (old) continental crust in the Midwest is more effective at transmitting seismic energy than (young) thin, hot crust in California. Earthquake Effects: Liquefaction *In areas where soils are saturated with water, seismic waves frequently cause water pressure to dramatically increase. *This results in liquefaction, the reduction in strength and stiffness of soil (the solid soil behaves more like a liquid, hence the name.) *Liquefaction has 2 major consequences 1) Building built on unconsolidated sediment will suffer significant damage as supports sink unevenly into the soil 2) Water underground may burst through to the surface where pressure is released. Damage from Earthquakes *The extent of damage from an earthquake commonly hinges on the geology: rock/ soil of contrasting mechanical properties or degree of water saturation Earthquake Effects: Tsunami *A tsunami is a giant wave or sequence of waves produced by large water disparities. These are most commonly caused by underwater earthquakes *Tsunamis can be destructive long distances from their source. US Quakes *OF the 15 largest earthquakes in the US recorded history (since seismographs were available in 1880’s) *8 in Alaska *3 in New Madrid (1811 ranks #5) Seismic Risk *If earthquakes usually come from movement on faults, and faults are most active at plate margins, then why are there such seismic hazards within the North American plate. Earthquake effects: Tsunami *a tsunami is a giant wave or sequence of waves produced by large water disparities. These are most commonly caused by underwater earthquakes. *tsunamis can be destructive long distances from their sources US Quakes *of the U.S. 15 largest earthquakes in the U.S. in recorded history (since seismographs were available in 1880's) ­8 in Alaska ­3 in New Madrid (1811 ranks #5) Seismic risk *if earthquakes usually come from movement on faults and faults are most active at pate margins then why are there such such seismic hazards within the north American pate. Earthquake prediction *can we predict earthquakes Yes and no *they can be in the long term (tens to hundreds of years) *they cannot be predicted in the short term (hours or weeks) *hazards can be mapped to assess risk *developing building codes *land ­ use planning *disaster planning Long term earthquake prediction *probability of a certain magnitude earthquake occurring requires determination of seismic zones by: *mapping historical epicenter *evidence of modern or ancient earthquakes ­ evidence of seismicity­ fault scarps, sand volcanoes etc ­ historical records What's down there *the crust effectively hides the mantle from our direct observation. Hence, in order to study the deep interior of the earth, we need to have practical indirect methods *we talked previously about the importance of meteorites to understanding earths chemical differentiation, but we have other methods of answering questions about what we can't directly see in the deep earth Exposed sections and deep drilling *there are a few spots on the earth where segments of the upper mantle have been obducted (exposed by reverse faulting) *these are ordinarily imperfectly preserved as a result of the deformation involved in their ascent to the surface *we can drill deep into the crust to investigate what lies beneath *drill holes are expensive * the deepest ever drill hole is only 12km; continental crust averages 45­2km thick Mantle xenoliths *xenoliths are pieces of deep rock transported up to the crust in magmas. Mantle xenoliths are relatively common and give us deeper samples than from exposed sections or drilling *xenoliths give a biased sample of the mantle *the deepest xenoliths are from the upper part of the mantle (not lower our middle) Mantle simulation *technology allows us to experimentally simulate extreme pressures and temperatures of even the deep mantle *experiments are still very difficult *experiments are mainly done on simplified systems which don't replicate the earth in detail Seismic revelation of deep earth structure *for all their practical applications the greatest contribution to understanding earth by seismology (study of earthquake waves) is in the definition of the nature of the interior of the planet Key principles to apply: *s­ waves don't propagate through liquids, p­ waves do, although more slowly than in solids *seismic energy goes faster through cold materials than hot *seismic velocity is proportional to density of material Reflection and refraction * when a Ray hits a boundary between 2 materials, the ray can undergo: *reflection:bounce off the boundary *refraction:bending as it passes through boundary Seismic revelation of deep earth structure *seismic waves travel curved paths through the earth because of the differences in wave velocity in the materials through which they pass Seismic velocities in deep earth P wave velocity: ­asthenosphere=6­211km/s ­lower mantle=11­13km/s ­ outer core=7­9km/s ­ inner core=11km/s The crust ­ mantle boundary (Moho) *discovered by Andrija mohorovicic in 1919 *based on average speed of seismic waves recorded at different distances from the epicenter Structure of the mantle *low velocity zone occurs beneath Oceania crust from 100­200km *below the low velocity zone under oceans and throughout mantle under continents seismic wave velocity increases with depth *upper mantle: above 660km *lower mantle: below 660km *transition zone: 410­660km The core mantle boundary *discovered by Gutenberg in 1914 *p­wave shadow zone *p­waves don't arrive at seismometers between 103degrees and 143 degrees from the epicenter *due to the refraction of waves entering a material that slows theor velocity *consists of liquid outer and solid inner core *s­wave shadow zone *s­wave s don't arrive at seismometers between 103 & 180degrees *s­waves dont travel through liquids *solid inner core discovered by Inge Lehmann in 1936 *p­waves reflect off a boundary within the core *exact depth of inner core determined later by seismic waves created during nuclear explosions The core *the core has a solid inner part and liquid other part due to temperature and pressure conditions inside earth Seismic Tomography *seismic tomography produce 3D images of variations in seismic velocities in earths interior *images provide detail concerning mantle dynamics