GLY Exam 2 Study Guide Study online at quizlet com 196ae7 1 Anticline An upfold in the form of an arch usually paired with syncline 2 Apparent Polar Wandering As a continent moves over the Earth s surface successively younger rocks forming on and within that continent will record different palaeomagnetic positions which will vary according to the location of the continent when the rock was formed As a result the position of the poles preserved in rocks of different ages will apparently deviate from the current magnetic pole position By joining up the apparent positions of these earlier poles an apparent polar wander path is generated 3 Asthenosphere The region within the upper mantle between 100 and 200 there is some variation in these exact depths from place to place that is the zone where seismic velocities are actually lower than they are at slightly shallower depths From the decrease in the S wave velocities in this region it can be inferred that the peridotite has lost some of it s rigidity that it is more ductile and likely close to its melting point perhaps a small fraction has melted but the bulk of it is still solid 4 Axial Plane An imaginary plane that divides a fold as symmetrically as possible and that passes through the axis 5 Brittle A material that breaks under stress Low temperatures and high strain rates 6 Bulk Modulus A measure of the incompressibility of a material The more incompressible a material is the greater the value of the BULK MODULUS Everyone knows steel is more incompressible than blue cheese now you know why the bulk modulus of steel is greater than that of blue cheese 7 Compressional Squeezes rocks Stress 8 Continental Crust Plate Boundaries 10 Core Continental crust is far more heterogeneous and more felsic perhaps chemically like a diorite It is also less dense than the mafic oceanic crust which is why the continental crust stands high on the surface of the Earth while oceanic crust is lower 9 Convergent Boundaries along which a cooler dense plate sinks down into the asthenosphere beneath the other plate The strongest seismic discontinuity seen on the velocity vs depth graph is that which is located at a depth of about 2900 km Immediately below this P wave velocities are about 30 less than above it and S waves are completely attenuated This is the boundary between the outer core and the mantle 11 Crust In the ocean basins crust is thinner averaging 5 7 km thick On continents the M discontinuity which separates the crust from the mantle occurs at a depth of 25 30 km on average and even deeper beneath mountain belts The maximum thickness of continental crust nearly 70 km is reached in the Tibet Plateau of the Himalayan Mountains 12 Curie The temperature above which a material looses its permanent magnetism Temperature This is very far above the curie temperature of any known materials If a common bar magnet is placed in an oven and heated to 550oC it will be de magnetised 13 Dip The angle in degrees between a horizontal plane and the inclined plane measured down from horizontal 14 Distribution and depth Plate boundaries are most subject to frequent earthquakes where do most earthquakes occur and how deep are the foci Subduction zones tend to have the largest quakes Most foci are no deeper than 100 km because brittle behavior occurs only in the upper part of the lithosphere 15 Divergent Plate Boundaries Along some of their boundaries plates separate and basaltic magma derived from local melting of the asthenosphere rises to fill the void and cools to form new oceanic crust 16 Ductile A material that absorbs the stress by flowing High temperatures and low strain rates 17 Effect of Ground Shaking Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake subsidence Buildings can even sink into the ground if soil liquefaction occurs Buildings can also be damaged by strong surface waves making the ground heave and lurch Any buildings in the path of these surface waves can lean or tip over from all the movement The ground shaking may also cause landslides mudslides and avalanches on steeper hills or mountains all of which can damage buildings and hurt people 18 Elastic Limit A limiting stress beyond which a solid suffers permanent deformation and does not return to its original size or shape once the stress is removed 19 Elastic Moduli This proportionality constant It is an important physical property of the material 20 Elastic Strain When the strain a body undergoes is proportional to the stress applied the material is exhibiting elastic strain Apply a tensional stress to a rubber band and you will produce considerable elastic strain Release the stress and the rubber band returns to it s original dimensions It is the nature of elastic strain that it is recoverable elastically strained material returns to its original state when stresses are relaxed Under certain conditions rocks too behave as elastic materials 21 Epicenter The point on the Earth s surface directly above the focus 22 Factors other than Location More damage to a highly populated area intensity that effect the level of damage caused by earthquakes Magnitude Scientists assign a number to represent the amount of seismic energy released by an earthquake The Richter magnitude scale as it is known is logarithmic so each step up represents an increase in energy of a factor of 10 The more energy in an earthquake the more destructive it can be Depth Earthquakes can happen anywhere from at the surface to 700 kilometers below In general deeper earthquakes are less damaging because their energy dissipates before it reaches the surface Distance from the epicenter The epicenter is the point at the surface right above where the earthquake originates and is usually the place where the earthquake s intensity is the greatest Local geologic conditions The nature of the ground at the surface of an earthquake can have a profound influence on the level of damage Loose sandy soggy soil can liquefy if the shaking is strong and long enough for example Secondary effects Earthquakes can trigger landslides fires floods or tsunamis Architecture Even the strongest buildings may not survive a bad earthquake but architecture plays a huge role in what and who survives a quake 23 Fire Fires can be started by broken gas lines and power lines or tipped over wood or coal stoves They can be a serious problem especially if the water lines that
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