EARTHSC 2GG3 Lecture Notes - Lecture 4: Mercalli Intensity Scale, Seismometer, Waves
17 Dec 2019
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Document Summary
Earthquake motion or trembling of the ground caused by the sudden displacement of rock. Displacements are by plate tectonics, meteorites, ground movement: trembling: same place. Usually directly below: the focus is directly below the epicentre, measured by seismographs. E a r t h q u a k e m a g n i t u d e: measured by moment magnitude (mw) The scale is logarithmic and based on powers of ten: ground motion for a m3 is 10 times that of a m2, amount of energy released for a m 3 is 32 times that of a m2. Smaller earthquakes are more frequent than larger ones. Shake maps use seismograph data to show areas of intense shaking. Earthquakes commonly occur at or near plate boundaries. Plate boundaries may contain faults: when stress on rocks exceeds their strength, the resulting rupture produces seismic waves. Friction along plate boundaries exerts strain or deformation.
