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Earthquakes and Seismicity

Earthquakes are caused by the sudden release of slowly accumulated strain energy along a fault in the earth’s crust. Earthquakes and volcanoes occur most commonly at the collision zone between tectonic plates. Earthquakes represent a particularly severe threat due to the irregular time intervals between events, lack of adequate forecasting, and the hazards associated with these:

  • Ground shaking is a direct hazard to any structure located near the earthquake’s center. Structural failure takes many human lives in densely populated areas.
  • Faulting, or breaches of the surface material, occurs as the separation of bedrock along lines of weakness.
  • Landslides occur because of ground shaking in areas having relatively steep topography and poor slope stability.
  • Liquefaction of gently sloping unconsolidated material can be triggered by ground shaking. Flows and lateral spreads (liquefaction phenomena) are among the most destructive geologic hazards.
  • Subsidence or surface depressions result from the settling of loose or unconsolidated sediment. Subsidence occurs in waterlogged soils, fill, alluvium, and other materials that are prone to settle.
  • Tsunamis or seismic sea waves, usually generated by seismic activity under the ocean floor, cause flooding in coastal areas and can affect areas thousands of kilometers from the earthquake center.
destruction caused by the earthquake
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