The first observations of free oscillations of the Earth were done during the great 1960 earthquake in Chile.
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A slight, but detectable, incessant excitation of the Earth's free oscillations, or normal modes, with periods in the range 30 to 1000 s, and is often referred to as the " Earth hum ".
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By February 2005, the earthquake's effects were still detectable as a complex harmonic oscillation of the Earth's surface, which gradually diminished and merged with the incessant free oscillation of the Earth more than 4 months after the earthquake.
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Chapters outline basic theorems in dynamic elasticity, representation of seismic sources, elastic waves from a point dislocation, plane waves in homogeneous media and their reflection and transmission at a plane boundary, reflection and refraction of spherical waves; Lamb's problem, surface waves in a vertically heterogeneous medium, free oscillations of the Earth, body waves in media with depth-dependent properties, the seismic source : kinematics, the seismic source : dynamics, and principles of seismometry
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