Seismic waves are the Earth's way of communicating earthquakes. They come in two flavors: body waves that zip through the planet's interior, and surface waves that ripple along its skin. Each type has its own quirks and impacts on structures.

P-waves and S-waves are the speedy body waves, while Love and Rayleigh waves are the slower but more destructive surface waves. Understanding how these waves move and change is key to predicting earthquake effects and designing safer buildings.

Types of Seismic Waves

Body waves vs surface waves

• Body waves penetrate Earth's interior propagating faster than surface waves
• P-waves and S-waves comprise two main types of body waves
• Surface waves travel along Earth's surface moving slower than body waves
• Love waves and Rayleigh waves make up two primary types of surface waves
• Surface waves generally exhibit larger amplitudes causing more structural damage
• Body waves decay more rapidly with distance compared to surface waves

Properties of P-waves and S-waves

• P-waves (Primary waves) compress and expand material as fastest seismic waves
• P-waves propagate through solids, liquids, and gases (rock, water, air)
• P-wave particle motion aligns parallel to wave propagation direction
• P-wave velocity in typical rock calculated as $V_p = \sqrt{\frac{K + \frac{4}{3}\mu}{\rho}}$
• S-waves (Secondary waves) create shear deformation moving slower than P-waves
• S-waves travel only through solids (rock, not water or air)
• S-wave particle motion occurs perpendicular to wave propagation direction
• S-wave velocity in typical rock determined by $V_s = \sqrt{\frac{\mu}{\rho}}$

Wave Propagation and Attenuation

Wave propagation through Earth

• Wave propagation transfers energy through a medium
• Wavelength and frequency relate through velocity equation $v = f\lambda$
• Seismic waves travel as direct, reflected, or refracted paths
• Huygens' Principle states every wavefront point acts as new wave source
• Snell's Law describes wave refraction at interfaces: $\frac{\sin \theta_1}{V_1} = \frac{\sin \theta_2}{V_2}$
• Waves interact with Earth's layers through reflection and refraction at boundaries
• Wave velocity changes due to varying material properties in different layers

Factors in seismic wave behavior

• Geometric spreading distributes energy over larger areas as waves propagate
• Intrinsic attenuation converts energy to heat through internal friction
• Dispersion varies wave velocity with frequency, spreading wave packets over time
• Material properties (density, elasticity) influence attenuation and dispersion
• Heterogeneity of the medium affects wave behavior
• Frequency content of seismic waves impacts propagation characteristics
• Quality factor (Q) measures energy loss per cycle, higher Q indicates lower attenuation
• Attenuation relationships in seismic hazard analysis account for energy loss with distance from source