Near-Surface Seismic Characterization using Three-Component Buried Geophones

Dan Cieslewicz


Two seismic field experiments were performed to determine whether shear wave attenuation in the near surface is responsible for the significant converted-wave bandwidth reduction observed in most multi-component land surveys. The experiments consisted of three-component geophones buried to depths of about 6, 12 and 18m that recorded data during the shooting of a 2-D seismic line. A control geophone was also placed on the surface. The geophones did not detect any systematic difference in the bandwidth of converted-wave reflections between the different geophone depths and the surface. It is concluded that the majority of attenuation in the converted wave occurs below a depth of 18 meters. The buried geophone data were also used to determine the depth of the water table using interval Vp/Vs ratios, to demonstrate that the near-surface impedance gradient amplifies ascending reflections, and to indirectly infer the occurrence of a receiver ghost. A basic interpretation is also presented.

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