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Ultrasonic Wave-Propagation Characteristics and Polarization in Stainless Steel Weld Metal

Description: Ultrasonic inspections of austenitic stainless steel weld metal are particularly difficult because of the dendritic structure and anisotropy of the material. The acoustic properties of stainless steel weld metal are discussed. Data on frequency spectra and variations in longitudinal and shear velocities with wave-propagation direction are presented. The difference in detectability of artificial reflectors using shear waves of varying polarization is presented, and it is demonstrated that, in some cases, horizontally polarized shear waves can detect a reflector in the weld metal, whereas the traditional vertically polarized shear waves cannot.
Date: March 1978
Creator: Kupperman, D. S. & Reimann, K. J.
Partner: UNT Libraries Government Documents Department


Description: Strain gage instrumentation is reported of three Cowboy shots to measure the strain produced in salt by coupled and decoupled detonations. Linear array tests were made to develop a propagation law for strain, to determine particle velocity and acceleration in salt, to compare explosives, to determine the effect of impedance coupling between explosive and rock, and to investigate other seismic effects. Crater tests were made to determine the dynamic tensile breaking strength of salt. Tests were made to measure in situ, longitudinal (P) and shear (S) wave velocities and to calculate the dynamic elastic constants therefrom. Laboratory tests on core were made to determine the dynamic compressive and tensile breaking strength of salt. Physical properties tests were made under laboratory conditions for comparison with dynamic results. (W.L.H.)
Date: September 1, 1960
Creator: Nicholls, H.R.; Hooker, V. & Duvall, W.I.
Partner: UNT Libraries Government Documents Department


Description: In this project we have addressed the problem of energy partitioning at distances ranging from very local to regional for various kinds of seismic sources. On the local and regional scale (20-220 km) we have targeted events from the region offshore Western Norway where we have both natural earthquake activity as well as frequent occurrence of underwater explosions carried out by the Norwegian Navy. On the small scale we have focused on analysis of observations from an in-mine network of 16-18 sensors in the Pyhasalmi mine in central Finland. This analysis has been supplemented with 3-D finite difference wave propagation simulations in a realistic mine model to investigate the physical mechanisms that partition seismic energy in the near source region in and around the underground mine. The results from modeling and analysis of local and regional data show that mean S/P amplitude ratios for explosions and natural events differ at individual stations and are in general higher for natural events and frequency bands above 3 Hz. However, the distributions of S/P ratios for explosions and natural events overlap in all analyzed frequency bands. Thus, for individual events in our study area, S/P amplitude ratios can only assist the discrimination between an explosion or a natural event. This observation is supported by synthetic seismograms calculated for simple 1-D models which demonstrate that explosions also generate shear-wave energy if they are fired close to an interface with a strong material contrast (as is the case for most explosions), e.g., free surface or the ocean bottom. The larger difference in S/P ratios between earthquakes and explosions for higher frequencies can be explained by the fact that at low frequencies (larger wavelengths), discontinuities and structural heterogeneities in the explosion source region are stronger generators of converted S energy. The S*-phase, for example, is most ...
Date: January 31, 2006
Creator: Bungum, H.; Kvaerna, T. & Larsen, S.
Partner: UNT Libraries Government Documents Department

Characterization of Fracture Patterns in the Geysers Geothermal Reservoir by Shear-wave Splitting

Description: The authors have analyzed the splitting of shear waves from microearthquakes recorded by a 16-station three-component seismic network at the Northwest Geysers geothermal field, Geysers, California, to determine the preferred orientation of subsurface fractures and cracks. Average polarization crack directions with standard deviation were computed for each station. Also, graphical fracture characterizations in the form of equal-area projections and rose diagrams were created to depict the results. The main crack orientations within the steam field are predominantly in the N10{degree}E to N50{degree}E direction, consistent with expected fracture directions in a pull-apart basin created by sub-parallel right-lateral strike-slip faults related to the San Andreas fault system. Time delays range from 15--60 ms, similar to the time delays from previous studies at geothermal reservoirs. They have detected a significant increase in time delays between 1988 and 1994, which they attribute to widening of the cracks or filling of the cracks with fluid. Increase in production activities during this time also could have influenced this widening.
Date: September 15, 1999
Creator: Erten, D. & Rial, J. A.
Partner: UNT Libraries Government Documents Department