GEOL 240Lg 1st Edition Lecture 6 Outline of Last Lecture I Gallium Magnetic Data II Earth s Interior Illustration III Earth s Magnetic Field IV Declination V Rock Magnetism VI Currie Point VII Thermo remnant magnetization VIII Harry Hess IX Age of the Sea floor X Movie of past plate motions Outline Current Lecture I Polar Wander Curves Paleo North Poles for Europe and North America II 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 are stress force divided by the arts over which it is acting 6 1 195lbs 2 wide area 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 directions materials fail more easily intention then compression stresses inside the earth are always compressional can 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 3 and the footwall will be discussed in next lecture
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