ERTH 2415 Lecture Notes - Lecture 8: Mercalli Intensity Scale, Seismometer, Strong Ground Motion
16 Oct 2015
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Document Summary
Inputs: ground motion data, knowledge of regional geology. Seismic waves are attenuated rapidly: eastern north america has old rocks of the continental interior. Natural frequency - frequency at which the system oscillates when disturbed: soft sediments: < 1 hz, hard sediments: > 1 hz. Hard rock (natural frequency > 1 hz) are amplified by body waves. Soils (natural frequency < 1 hz) are amplified by surface waves: liquefaction - phenomenon in which the strength of soil is reduced by rapid and violent shaking, or loading. Occurs in saturated soils in which the space between particles is filled with water. Liquefied soil behaves like a liquid and does not have the strength to support a load. Consequences of liquefaction include building subsidence and mass movements. Structure might stay intact but sinks into ground: landslides, building style. Some materials fail abruptly: higher hazard: total collapse, examples: brick, stone. Some materials undergo plastic deformation before failing.
