Seismic S and P Waves: Production, Nature, and Propagation

Production of Seismic Waves

• Seismic waves are generated by the sudden release of energy during earthquakes, volcanic eruptions, or artificial explosions.
• The energy release occurs due to the fracturing or shifting of rock masses along fault lines.
• These waves travel through the Earth’s interior and surface, carrying information about its structure.

Nature of S and P Waves

1. P-Waves (Primary Waves):

   • Type: Longitudinal or compressional waves.
   • Particle Motion: Particles oscillate parallel to the direction of wave propagation.
   • Speed: Fastest seismic waves, traveling at approximately 6–8 km/s in Earth’s crust.
   • Mediums: Can travel through solids, liquids, and gases.

2. S-Waves (Secondary Waves):

   • Type: Transverse or shear waves.
   • Particle Motion: Particles oscillate perpendicular to the direction of wave propagation.
   • Speed: Slower than P-waves, traveling at 3–4 km/s in Earth’s crust.
   • Mediums: Can travel only through solids, as liquids and gases cannot support shear stress.

Propagation of Seismic Waves

1. P-Waves:

   • Travel through the Earth’s interior by compressing and expanding the medium.
   • The first to be detected by seismographs due to their speed.
   • Refraction occurs at boundaries between layers of different densities, such as the crust, mantle, and core.

2. S-Waves:

   • Travel through the Earth’s interior by shearing the medium.
   • Cannot pass through the liquid outer core, creating an S-wave shadow zone on the Earth’s surface.
   • Slower arrival times make them the second to be detected by seismographs.

Wave Behavior and Earth’s Structure

• Reflection and Refraction: Both wave types are reflected and refracted at boundaries within the Earth, such as the Mohorovičić discontinuity (Moho) and the core-mantle boundary.
• Shadow Zones: The liquid outer core prevents S-waves from passing, while P-waves are refracted, causing areas where neither wave type is detected.

Applications

• Seismic waves help scientists study Earth’s interior structure, including the core and mantle.
• They are critical for earthquake monitoring, determining the epicenter, and estimating earthquake magnitude.