GEOL 240Lg 1st Edition Lecture 6Outline of Last Lecture I. Gallium Magnetic DataII. Earth’s Interior IllustrationIII. Earth’s Magnetic FieldIV. DeclinationV. Rock MagnetismVI. Currie PointVII. Thermo- remnant magnetizationVIII. Harry HessIX. Age of the Sea floorX. “Movie” of past plate motionsOutline Current Lecture I. Polar Wander Curves/ Paleo-North Poles for Europe and North AmericaII. Review of what is an Earthquake?III. What are fault strikes?IV. Stress in Earthquakes Current Lecture- Apparent polar wander curves/ Paleo-north poles for Europe North America make no sense in their current locations, but track perfectly with one another through time if restored to their 300 Ma PANGEA configurations. - What is an earthquake? A sudden slippage - What’s a fault line? Are faults lines?They are 3 dimensional planes An earthquake starts at a point hypocenter, or the focus Fault strike: line of intersection between plane and horizontal ground surface Strike = - angle between fault trace and north Dip= angle between fault plane and earth’s surface Fault scarp: forms in the ground Stress+ its relationship to earthquakes Force= mas x a (acceleration)A= acceleration (usually gravity) mass stays the same wherever you arestress= force divided by the arts over which it is acting 6’1 195lbs2’widearea 12 sq. 195/12 ft^2= 195lbs/1728in^2= 0.11 psi stress in Earth is 3D isotropic stress= same in all directions- classic example is pressure exerted in 3D at bottom of a swimming pool- same thing happens inside earth real 3D stresses inside earth as a combination of isotropic component (always present) + tectonic component, which because we have plate motions is not the same in all directionsmaterials fail more easily intention then compression stresses inside the earth are always compressionalcan uniquely define the 3D state of stress of paint inside the Earth with 3 mutually perpendicular “ principal stresses’ normal stress =(sigma)shear stress (sigma s)increasing normal stress lamps the fault shut and moves the fault away from failure faults : how many type of plate boundaries are there? There are 3 primary types of Tectonic Plate boundaries: Divergent boundaries; Convergent boundaries; and Transform boundaries. As the giant plates move, diverging [pulling apart] or converging [coming together] along their borders, tremendous energies are unleashed resulting in tremors that transform Earth’s surface.While all the plates appear to be moving at different relative speeds and independently of each other, the whole jigsaw puzzle of plates is interconnected.how many faults 3and the footwall… will be discussed in next
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