Earthquakes waves arrive in a distinct sequence Different waves cause different

Earthquakes waves arrive in a distinct sequence

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Earthquakes waves arrive in a distinct sequence - Different waves cause different motion - P-waves are the first to arrive - They produce a rapid, bucking, up-and-down motion - S-waves arrive next (second) - They produce a pronounced back-and-forth motion - This motion is much stronger than that from P-waves - S-waves cause extensive damage - Surface waves are delayed travelling along the exterior - L-waves follow quickly behind the S-waves - They cause the ground to writhe like a snake - R-waves are the last to arrive - The land surface undulates like ripples across a pond - These waves usually last longer than the other kinds - R-waves cause extensive damage - Severity of shaking and damage depends on: - The magnitude (energy) of the earthquake - The distance from the focus - The nature of the subsurface material - Bedrock transmits seismic waves quickly = less damage - Sediments reflect and refract waves = amplified damage - The frequency of the earthquake waves - Ground shaking - Building floors “pancake” - Bridges and roadways topple
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- Bridge supports are crushed - Masonry walls break apart - Landslides and avalanches - Shaking causes material on steep slopes to fail - Hazardous slopes bear evidence of ancient slope failures - Landslides frequently accompany earthquakes in uplands - Liquefaction - waves liquefy H 2 O-filled sediments - Groundwater forces grains apart reducing friction - Liquefied sediments flow as a slurry - Sand becomes “quicksand”: clay becomes “quick clay” - Sand blows and sand volcanoes disrupt ground surface Liquefaction - Liquefaction causes soil to lose strength - Land, and the structures on it, will slump and flow - Buildings may founder and topple over intact Earthquake Damage - Fire is frequently realized earthquakes hazard - Shaking topples stoves, candles, and power lines - Broken gas mains and fuel tanks ignite a conflagration - Infrastructure (water, sewer, electricity, roads) destroyed - Firefighters are often powerless to combat fire - No road access, no water - Too many hot sports - Fire may greatly magnify the destruction and toll in human lives - Tsunami (Japanese for harbour wave) - Tsunamis result from displacement of the sea floor - Earthquakes, submarine landslide, or volcanic explosion - Faulting displace the entire volume of overlying water - A giant mound (or trough) forms on the sea surface - This feature may be enormous (up to a ten thousand square mile area) - Feature collapse creates waves that race rapidly away - Destructive tsunamis occur frequently - about one a year - There have been 94 destructive tsunamis through the 20 th century - They have caused about 350,00 human deaths - Future tsunami disasters are inevitable - Growing human population in low-lying coastal areas - Education about tsunamis can save many lives - Tsunamis race at jetliner speed across the ocean - They may be almost imperceptible in deep water - Low wave height (amplitude), long wavelength (frequency) - As water shallows, waves slow from frictional drag - Waves grow in height, reaching 10 to 15m or even more
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- Tsunami waves are very different from wind-driven waves - Wind waves - Influence the upper 100m - Have wavelengths of several tens to hundred of m - Wave height and wavelength related to wind speed - Wave velocity maximum several tens of km per hour - Waves break in shallow water and expend all stored energy - Tsunami waves - Influence entire water depth -
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