DTIC ADA192315: Stochastic Geologic Effects on Near pdf

DTIC ADA192315: Stochastic Geologic Effects on Near

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Analysis of accelerograms recorded at the 20-m range from a buried 5- lb detonation in alluvium revealed wide (as large as 20 dB in the amplitude modulus of the Fourier transform) variations in response for frequencies above 35 Hz. Additional experiments were performed which ruled out source asymmetry or instrumental irregularity as the cause of these variations. The observations suggest that scattering by geologic inhomogeneity is responsible for the frequency-dependent spatial variability in ground motion. A thorough understanding of the physical processes responsible for this variability requires that a quantitative relationship be established between the subsurface material property information and the observed ground motion characteristics. An attempt was made to do this using available standard penetration test (SPT) data from the test-bed where the initial experiment was detonated. Autocorrelations of the blow count data from the SPT test were computed and compared with theoretical exponential and Gaussian distributions.

The exponential distribution with a scale length between 2.0 and 3.0 m best matched the data. Assuming the Born approximation, a scale length of 2.0 to 3.0 m implies that significant scattering should occur above 10 Hz. The recorded ground motions are, however, coherent out to about 35 Hz, suggesting a scale length of 0.5 to 1.0 m, which is beyond the resolution of the SPT technique. This scale length is not unreasonable in light of the general geologic characteristics of the test area

• Creator/s: Defense Technical Information Center
• Date: 11/1/1987
• Year: 1987
• Book Topics/Themes: DTIC Archive, Reinke, R E, AIR FORCE WEAPONS LAB KIRTLAND AFB NM, *ALLUVIUM, *GROUND MOTION, *STRUCTURAL GEOLOGY, *SEISMIC ARRAYS, FOURIER TRANSFORMATION, FREQUENCY, SOURCES, SPATIAL DISTRIBUTION, SCATTERING, STOCHASTIC PROCESSES, ACCELERATION, RESOLUTION, COUNTING METHODS, AUTOCORRELATION, EXPLOSION EFFECTS, GEOLOGY, VARIATIONS, SEISMIC DATA, PENETRATION, SCALE, LENGTH, SEISMIC WAVES, HETEROGENEITY, STATISTICAL DISTRIBUTIONS, EXPONENTIAL FUNCTIONS, INCOHERENT SCATTERING, AZIMUTH, DRY MATERIALS, SPECTRUM ANALYSIS, TEST FACILITIES, SUBSURFACE, NEAR FIELD, HIGH EXPLOSIVES, DISTRIBUTION FUNCTIONS, NORMAL DISTRIBUTION

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