Fundamental Considerations
Seismic Waves
Wave Terminology - amplitude, frequency, and wavelength; velocity equal to frequency times wavelength.
Elastic Coefficients - Youngís modulus, Poissonís 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
Ray Paths
Reflection, Refraction, and Snellís 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
Wave Attenuation and Amplitude
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
Energy Sources
Types - hammer strike, shotgun, weight drop, air gun or sparkers (energy and frequency content). Most energy has frequencies of 600 Hz or less
Seismic Equipment
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).