Browsing by Subject "Rayleigh waves"
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Item A ray path explanation for RG waves from earthquakes(Texas Tech University, 1983-05) Ismail, Mohamad Izham BNot availableItem Crustal Structure of the Central High Plains of Texas from Rayleigh Wave Dispersion(Texas Tech University, 1972-12) Stanton, James CliffordNot Available.Item Determination of Longitudinal Stress in Rails(2012-02-14) Djayaputra, FerdinandThe objective of this research is to determine the longitudinal stress in rails by using the polarization of Rayleigh waves. Analytical models are developed to describe the effect of applied stress on wave speed and on the polarization of Rayleigh waves. A numerical simulation is performed to find the effect of applied stress on wave velocity and Rayleigh wave polarization. The effect of uncertainties in material properties on wave velocity and polarization of Rayleigh wave is also examined in the simulation. The experiment uses a laser Doppler vibrometer (LDV) to measure the particle velocities. The in-plane and out-of-plane velocity components are obtained from the measured particle velocities. The polarization of Rayleigh wave, which is defined as the ratio between the in-plane and out-of-plane displacements, is calculated. Furthermore, the polarization of the Rayleigh wave is considered as a measure to identify applied stress. The experiment is performed on unstressed and stressed rail specimen. Thus, Rayleigh wave polarization is obtained as a function of applied stress. The experimental results are compared with the analytical model. The result shows a good agreement with the theoretical values for unstressed rail.Item Discussion of RG propagation in terms of ray paths of P and SV(Texas Tech University, 1984-08) Finlay, Corey DaneNot availableItem Dispersion of short period Rayleigh waves in the Atlantic Ocean(Texas Tech University, 1981-12) Harrison, Ben SEighteen earthquakes, recorded at Bermuda, from in front of and behind the West Indian Island Arc and near the Mid-Atlantic Ridge were analyzed. Short-period Rayleigh waves propagating from earthquakes in front of Puerto Rico and the Virgin Islands have apparent velocities which indicate that the energy travels from the epicenters as a P-phase to the steep wall of the Puerto Rico trench where it is transformed to Rayleigh first shear mode. Short-period Rayleigh waves from the Windward Passage exhibit slower apparent velocities indicating that they travel from epicenter through the Bahamian Platform in the fundamental Rayleigh mode where they are transformed to travel through oceanic structure in the first shear mode. Earthquakes from the Mid-Atlantic Ridge between 22°N and 31°N latitude produced only Rayleigh waves with periods of 16 seconds or greater. These waves are in fundamental Rayleigh mode in an environment of high attenuation of short period energy. Earthquakes in the Windward and Leeward Islands behind the West Indian Arc produce only Rayleigh waves with periods of 17 seconds or greater which are also propagated in the fundamental mode, and short-period energy is strongly attenuated before transformation to the first shear mode becomes possible.Item Energy distribution of Rayleigh waves in the crust and upper mantle(Texas Tech University, 1984-08) Drake, Jerry TNot availableItem Finite element study of vibration isolation using an underground trench(Texas Tech University, 1997-08) Wu, GuanghuaThe purpose of this dissertation is to evaluate the performance of the underground trench as a barrier to isolate structures from surface vibrations. The tool used to perform this evaluation is the Finite Element Method (FEM). A two-dimensional (2D) FEM computer program was developed and verified by comparing its results to those of well known theoretical and experimental vibration results: for a one-dimensional (ID) beam; for a 2D plate in plane stress; and, for the open trench. The FEM code was found to agree reasonably well for all three well-characterized theoretical and experimental results obtained by other researchers. It was then used to investigate the usefulness of the underground trench, a new concept for surface vibration isolation of structures. In performing the evaluation of surface vibration effectivenes of the underground trench a general criterion based on surface vibration amplitude was developed. This general criterion allowed judging the effectiveness of a particular underground trench configuration on a quantitative basis, permitting comparisons to be made which are consistent for different underground trench configurations. The effectiveness of the underground trench structure was then studied in detail. Use was also made of the Taguchi Method for Experiment Design to minimize the number of computer runs that needed to be made, while at the same time optimizing the design parameters that define an underground trench. The results obtained show that the underground trench structure is as effective as the open trench in isolating structures from surface vibrations.Item Propagation of high frequency P and S waves under oceanic structures(Texas Tech University, 1993-12) Cakir, OzcanThe high frequency Po and So seismic waves observed at long distances under deep oceanic basins are investigated by means of numerical simulation. These waves are propagated particularly along the ray paths in relatively homogeneous and tectonicly stable regions of oceanic crust and upper mantle, and in continental shield areas. Propagation is terminated by structures such as midocean ridges, deep ocean trenches, and continental mountain chains. When expected variability in crust and upper mantle velocity depth structure is disrupted by such structural discontinuities, Po and So waves seize to travel. The seismic wave guide of crust and upper mantle may be continuous for hundreds of kilometers, as is the case in oceanic basins and continental shields. For these seismic ray paths, the wave guide is so efficient that waves recorded at large distances (as large as 3000 km or more) could include frequencies as high as 35 — 40 Hz. The long coda duration of 1 — 2 minutes is typical in these phases. The apparent velocity varies around 8.3 km/sec. for Po and 4.7 km/sec. for So. A special name, Po and So, has been given to these high frequency waves because of their predominance along oceanic paths.Item Rayleigh wave model of crustal structure of northeaster Mexico(Texas Tech University, 1978-08) Pinkerton, Roger ParrishNot availableItem Synthetic seismograms and character modeling: an aid to the determination of the earth's structure from Rayleigh waves(Texas Tech University, 1980-05) Crider, Richard LNot available