Seismic Waves

Wave Terminology - amplitude, frequency, and wavelength; velocity equal to frequency times wavelength.

Elastic Coefficients - Young’s modulus, Poisson’s ratio, Bulk Modulus, and Shear/Rigidity Modulus

Seismic Waves - P, S, and Surface

Seismic Wave Velocity - representative values for rock types (200-5000 m/s) and relationship to elastic coefficients

Reflection, Refraction, and Snell’s Law - wave energy is reflected or bent across an interface. The angle of reflection or refraction depends on the angle of incidence and the ratio of the velocities across the interface.

Critical Refraction - wave is refracted parallel to the interface

Diffraction - new waves are generated in all directions when a wave hits a sudden change in an interface (e.g., fault) that is the same size as the wavelength

Wave Arrivals - Air wave, direct wave, ground roll, reflected wave, and head wave

Spherical Spreading - energy per area decreases as the wave moves outward in all directions

Absorption - some wave energy is converted into heat energy as the wave deforms the media. Absorption is frequency/wavelength depended. Short wavelength/high frequency waves lose more energy.

Energy Partitioning - energy of incident wave is divided among the reflected, refracted or convert waves

Types - hammer strike, shotgun, weight drop, air gun or sparkers (energy and frequency content). Most energy has frequencies of 600 Hz or less

Geophones - how they work (ground motion converted into electrical signal) , natural frequency, critically damped

Recording/Conditioning - digital/analog filtering, relationship between frequency and resolution, reducing noise relative to signal by multiple shots (constructive and destructive interference).