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1. A slowing down or opposition to oscillation caused by dissipation of the oscillation energy. (a) Critical damping, μc, is the minimum damping that will prevent oscillation from taking place. (b) The damping factor μ is the ratio of the system friction to that necessary for critical damping, or the quotient of the logarithm of the ratio of two successive oscillations if the system is underdamped. The damping factor is one for critical damping, less than one for an underdamped system (which will oscillate), and greater than one for an overdamped system. See Figure D-1. (c) Most geophones are slightly underdamped, often having optimum damping that is 0.66 μc, which provides the most rapid convergence. 2. Site damping is concerned with natural resonances and the response to standing-waves. Site damping can be thought of as either the rate of amplitude decrease after cessation of excitation or as the decrease in amplitude response as the excitation frequency differs from the resonant frequency. Measuring damping and Q generally requires the use of controlled vibrators.