– E.g. Denver, waste water from a military installation was pumped into a deep well causing earthquakes. Also happened in Ohio – When valleys are flooded to make reservoirs (e.g. Lake Mead, NV&AZ) the additional groundwater pressure can lubricate faults in the region. Also the weight of the lake may bend the land forming normal faults.
Ground Shaking and Displacement During an Earthquake Displacement – a few mm- a few meters Acceleration – 0 – 2 g’s Most Damage Longest Lasting
Severity of Shaking Depends On: • Magnitude of the earthquake • Distance from hypocenter • The nature of the substrate at your location – Unconsolidated rock shakes a lot more, basins can amplify waves • E.g. 1985 Mexico city M8.0 300 km away • The frequency of the seismic waves – High frequency waves do most damage but do not travel very far • Car stereo analogy (bass) • [TerraShake Animations]
Buildings - Mexico City, 1985 Before After
Secondary Effects of Earthquakes • Earthquakes can also cause landslides • Especially bad in California where faults have uplifted shorelines very quickly before the rock had time to completely lithify • California will not sink into the sea, but homes on the coast may.
More Secondary Effects • An earthquake may cause wet sediment to liquefy. This is called liquefaction – Similar to quicksand Liquefaction after an earthquake in Taiwan
Liquefaction • Liquefaction can occur on a large scale • The ground may separate into several coherent slump blocks if a basal layer liquefies. • This happened to a housing development after a large earthquake near anchorage Alaska in 1964.
Turnagain Heights Disaster, AK 1964
Sand Volcanoes / Sand Boils • Shaking during an earthquake can also mobilize sand layers creating sand boils or sand volcanoes , which may eject sand 10 m into the air during an earthquake.
Fire! • Earthquakes can break gas lines and knock down power lines causing numerous fires. • Fires were responsible for most of the deaths during the 1906 great San Francisco earthquake
Fire - San Francisco, 1906
Tsunamis • Tsunami: a large wave that is generated by an earthquake , landslide, or meteor impact – Not “Tidal Waves”; They have nothing to do with tides – Result when earthquakes cause a large vertical displacement of the seafloor. – Water rushes in to fill the lowered points; a wave is formed – Associated with normal and reverse faults • Subduction zones can produce the largest earthquakes (most slip and rupture length) they can also generate the largest tsunamis
Tsunami Occurrence • Destructive tsunamis occur frequently - about 1/yr. • Many tsunami disasters dot recorded history. – 94 destructive tsunamis in the last 100 years.
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- Earthquakes, Seismic Waves