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IN‐SITU INVESTIGATION OF SEISMIC BODY WAVE ATTENUATION IN HETEROGENEOUS MEDIA *
Author(s) -
NEWMAN P. J.,
WORTHINGTON M. H.
Publication year - 1982
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1982.tb01312.x
Subject(s) - attenuation , geology , geophone , lithology , shear waves , shear (geology) , mineralogy , seismogram , seismology , anelastic attenuation factor , seismic wave , anisotropy , borehole , absorption (acoustics) , petrology , geotechnical engineering , optics , composite material , materials science , physics
A bstract Field experiments have been carried out to study the nature and magnitude of seismic wave attenuation for a variety of lithologies. In each survey two three‐component sets of geophones with wall clamping mechanisms were lowered down boreholes and signals originating from surface compressional and shear‐wave sources were recorded. The data collected were corrected for spherical divergence and analyzed to determine intrinsic attenuation. For situations of anomalous wavefront expansion and in cases where multiple reflection losses may be significant, corrections were supplied by a synthetic seismogram programme to improve the estimates of intrinsic attenuation. Values of attenuation were obtained for pure sandstone, sandstone‐marl sequences and fissured‐unfissured chalk sequences. These formations were all near surface and relatively porous. Significant differences in the relative values of compressional and shear‐wave attenuation in the various lithologies were noted. In particular compressional absorption in the fissured zones of chalk was twice the absorption associated with the seismic velocities and the absorption of shear waves fluctuated much less. A large contrast in P‐wave attenuation was also observed between pure Bunter Sandstone and the sandstone‐marl sequence (absorption was over three times as small in the former). A smaller contrast was noted for shear attenuation. The results obtained suggest that, for the relatively homogeneous formations such as pure sandstone and “unfissured” chalk, “shear” absorption was dominant over “bulk” absorption. In contrast bulk absorption was larger than shear absorption for other formations, e.g. the “fissured” chalk sequences and a “partially saturated” chalk section. Attenuation was found to be approximately proportional to frequency in all experiments.