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Geosciences LibreTexts

9: Earthquakes

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    • 9.1: Earthquake Essentials
      Earthquakes are felt at the surface of the Earth when energy is released by blocks of rock sliding past each other, i.e. faulting has occurred. Seismic energy thus released travels through the Earth in the form of seismic waves. Most earthquakes occur along active plate boundaries. Intraplate earthquakes (not along plate boundaries) occur and are still poorly understood. The USGS Earthquakes Hazards Program has a real-time map showing the most recent earthquakes.
    • 9.2: Measuring Earthquakes
      People feel approximately 1 million earthquakes a year, usually when they are close to the source and the earthquake registers at least moment magnitude 2.5. Major earthquakes of moment magnitude 7.0 and higher are extremely rare. The U. S. Geological Survey (USGS) Earthquakes Hazards Program real-time map shows the location and magnitude of recent earthquakes around the world.
    • 9.3: Earthquake Risk
      Earthquake magnitude is an absolute value that measures pure energy release. Intensity, however, i.e. how much the ground shakes, is determined by several factors. In general, the larger the magnitude, the stronger the shaking and the longer the shaking will last. Shaking is more severe closer to the epicenter. The severity of shaking is influenced by the location of the observer relative to the epicenter, the direction of rupture propagation, and the path of greatest rupture.
    • 9.4: Case Studies
      This section contains multiple case studies of major earthquakes in North America as well as historically important earthquakes in the whole world.

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