Seismic Waves Overview

Overview

This lecture explains seismic waves produced by earthquakes, focusing on their types, characteristics, and effects on Earth's surface and structures.

Seismic waves are energy waves released by earthquakes, spreading out in all directions from the focus.
The focus is the point within the Earth where the rock breaks and the earthquake originates.

Seismic waves are categorized into body waves (P and S waves) and surface waves.

P (Primary) Waves are the fastest, arrive first, and are compressional waves causing particles to move parallel to wave direction.
P waves can travel through solids, liquids, and gases.
S (Secondary) Waves are slower than P waves, arrive second, and are shear waves moving particles perpendicular to the wave direction.
S waves can only travel through solids and cannot pass through liquids or gases.

Surface waves are the slowest and arrive last during an earthquake.
They cause the most intense shaking and structural damage due to their large amplitudes.
Two main types are Love (L) waves (move ground side to side) and Rayleigh (R) waves (roll ground up and down).
Surface waves are most destructive at the Earth's surface and diminish with depth.

Seismographs record the arrival of P, S, and surface waves at different times and amplitudes.
The farther a seismograph is from the earthquake focus, the larger the time gap between wave arrivals and the smaller the wave amplitudes.

Seismic Waves — waves of energy released during an earthquake.
Focus — the point within the Earth where an earthquake originates.
Body Waves — seismic waves that travel through Earth's interior (includes P and S waves).
P (Primary/Pressure) Waves — fastest seismic waves; compressional; move through solids, liquids, and gases.
S (Secondary/Shear) Waves — slower than P waves; shear motion; move only through solids.
Surface Waves — slowest waves; travel along Earth's surface; cause most damage.
Seismograph — instrument that records seismic wave arrivals and amplitudes.