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1. Quality factor, the ratio of 2π times the peak energy to the energy dissipated in a cycle; the ratio of 2π times the power stored to the power dissipated. The seismic Q of rocks is of the order of 50 to 300. Q is related to other measures of absorption (see below):

where V, f, λ, and T are, respectively, velocity, frequency, wavelength, and period (see Sheriff and Geldart, 1995: 60, 177[1]). The absorption coefficient α is the term for the exponential decrease of amplitude with distance because of absorption; the amplitude of plane harmonic waves is often written as

where x is the distance traveled. The logarithmic decrement δ is the natural log of the ratio of the amplitudes of two successive cycles. The last equation above relates Q to the sharpness of a resonance condition; fr is the resonance frequency and Δf is the change in frequency that reduces the amplitude by 1/√2. The damping factor h relates to the decrease in amplitude with time,

See also Figure A-2.

Absorption terminology. Sometimes this terminology is used for attenuation because of factors other than absorption. E = energy, ΔE = energy lost in one cycle, λ = wavelength, f = frequency, x = distance, t = time, A/A0 = amplitude/(initial amplitude), A1/A2=amplitude/(amplitude one cycle later). (From Sheriff, 1989, p 330[2])

2. The ratio of the reactance of a circuit to the resistance. 3. A term to describe the sharpness of a filter; the ratio of the midpoint frequency to the bandpass width (often at 3 dB). 4. A designation for Love waves (q.v.). 5. Symbol for the Koenigsberger ratio (q.v.). 6. See Q-type section.

See also


  1. Sheriff, R. E. and Geldart, L. P., 1995, Exploration Seismology, 2nd Ed., Cambridge Univ. Press.
  2. Sheriff, R, 1989, Geophysical methods: Prentice Hall Inc.