SEISMIC ATTENUATION OF GULF COAST SEDIMENTS

Abstract

Previous efforts to measure the attenuation of seismic energy as it propagates vertically through the earth have been restricted to thick, isotropic, homogeneous sections of material. Values have now been obtained from normally layered Gulf Coast sediments. After normalizing with respect to the shot, the spectra of many traces over a small interval in depth can be averaged to minimize reflection interference and to yield a frequency response function associated with a given depth. Except for the measurements in the low velocity layer (LVL), a cemented array of geophones 1000 ft deep was used. The LVL measurements were made using individually cemented geophones. Data were taken on a digital recorder using a 0.5 ms sampling rate, and the processing was performed on a digital computer. Attenuation was found to vary exponentially with frequency to the first power in the range from 50 to 400 Hz. The 1000‐ft section of earth, made up largely of clay and sand layers, was separated into four sections at depths of 10, 100, and 500 ft. Attenuation in db/wavelength was found to be 13.1, 0.1508, 0.3641, and 0.2004 in the respective sections.