Earthquakes & Earth's Interior

Earthquakes & Earth's Interior

Overview of Earthquakes

  • Earthquakes occur when there is a sudden release of energy in the Earth's crust, resulting in seismic waves.
  • They can be caused by various tectonic processes and can vary significantly in magnitude and impact.

Earthquakes & Plate Tectonics

  • Seismic Activity: Maps show data for earthquakes (M2.5+) occurring continuously.
  • Earthquake Behavior: Earthquakes are often associated with plate boundaries where they occur due to tectonic movements.
Earthquake Distribution Locations
  • Plate Boundaries: Most earthquakes occur along:
    • Divergent Boundaries: Least damaging, caused by tension (e.g., mid-ocean ridges).
    • Transform Boundaries: Intermediate damage, caused by shear motion (e.g., San Andreas Fault).
    • Convergent Boundaries: Most damaging, caused by compression resulting in subduction zones.

Mechanisms of Earthquake Generation

  • Divergent Boundaries:

    • Characteristics: Least damaging, tension-filled motion.
    • Examples: Normal faults, rift valleys.

  • Transform Boundaries:

    • Characteristics: Intermediate damage due to horizontal movement.
    • Examples: San Andreas Fault where Pacific Plate moves relative to North American Plate.

  • Convergent Boundaries:

    • Characteristics: Most destructive, usually associated with subduction.
    • Earthquake Depth and Impact: Typically leads to larger seismic events due to compression forces.

Earthquake Types Outside Plate Boundaries

  • Intraplate Earthquakes:
    • Occur within a tectonic plate rather than at the boundaries.
    • Often in ancient plate boundaries which are weaker due to historical tectonic activity.

Elastic Rebound Theory

  • Creep Motion:

    • Smooth and gradual motion that often goes unnoticed and causes minimal to no damage.

  • Elastic Rebound:

    • Process of stress build-up causing the fault to deform and then suddenly release energy, snapping back to original shape.
    • Explains how potential energy accumulated in faults is released during an earthquake.

Seismic Wave Transmission

  • Seismic Waves: Generated during an earthquake that transmit energy.

    • Body Waves: Travel through the Earth's interior (Primary - P waves, Secondary - S waves).
    • Surface Waves: Travel along the Earth's surface (Love and Rayleigh waves).

  • P Waves:

    • Fastest, travel through solids, liquids, and gases, causing compressional movements.

  • S Waves:

    • Slower, can only move through solids, causing shear movements perpendicular to the wave direction.

Utilizing Seismometers

  • Seismometer Functionality:

    • Detects vertical and horizontal seismic waves; can also utilize consumer technology (e.g., smartphone apps).

  • Seismic Measurements:

    • Records arrival times of different seismic waves to calculate epicenter locations.