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.