Geography 2152F/G Lecture Notes - Lecture 7: Mercalli Intensity Scale, San Andreas Fault, Seismic Wave
22 Apr 2016
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Document Summary
Result from rupture of rocks along a faultline. Energy is released in the form of seismic waves. Epicenter: at the surface above where the rupture forms. Compared by magnitude: 1 decimal place, richter scale (1935) Measure of the strength of a wave at 100km from the epicenter. More accurate methods have been developed: moment magnitude scale (m) Determined by the area ruptured along a fault. Frequency: several minor every hour, only one >8 every year, strongest ever recorded m9. 5 in chile. Intensity: modified mercalli intensity scale is a qualitative scale based on effect to structures and people (12 categories) Friction exerts a force (stress) on the rocks, exerting strain or deformation. Motion at boundaries is not usually smooth or constant. When the stress exceeds the strength of the rocks, there is a sudden movement along the fault. Movement (rupture) starts at the focus and propagates in all directions, called seismic waves. Strike-slip fault: displacements are horizontal, san andreas.
