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Norman Ricker did important work on determining the shape that the seismic pulse acquires as it propagates through rock (Ricker, 1940[1], 1941[2], 1953[3]). His equations predicted the waveform that would be observed after an impulsive signal has traveled a given distance through an absorbing material. Ricker’s work included first-power, second-power, and fourth-power frequency dependence of the absorption coefficient. He found that the wave’s shape for second-power frequency dependence most closely resembled what could be measured at the time in the field. Such a second-power frequency dependence suggested to him a “viscoelastic” frictional-loss mechanism of a type that usually is associated with viscous liquids. From that attenuation law, Ricker gave equations that generated waveforms for ground displacement and for particle velocity. At large distances from the source, such a waveform becomes symmetric. In his honor, this waveform is now called the Ricker wavelet.

  1. Ricker, N., 1940, The form and nature of seismic waves and the structure of seismograms: Geophysics, 5, 348–366.
  2. Ricker, N., 1941, A note on the determination of the viscosity of shale from the measurement of wavelet breadth: Geophysics, 6, 254–258.
  3. Ricker, N., 1953, The form and laws of propagation of seismic wavelets: Geophysics, 18, 10–40.