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All-sky polarization imager deployment at Mauna Loa Observatory, HawaiiDahlberg, Andrew Richard. January 2010 (has links) (PDF)
Thesis (MS)--Montana State University--Bozeman, 2010. / Typescript. Chairperson, Graduate Committee: Joseph A. Shaw. Includes bibliographical references (leaves 74-77).
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A long period Rayleigh wave experiment in the Vancouver Island regionPareja, German J. January 1975 (has links)
A study of the dispersion of long-period Rayleigh waves was proposed in order to acquire additional knowledge about the lithospheric structure of the Vancouver Island region.
Three portable, long-period seismographs were designed and built to operate in field conditions. An array was established with stations at Victoria, Vancouver and Quadra Island; during six weeks of operation, several earthquakes were recorded, of which two were aligned conveniently with the array. Another network with stations at Ucluelet, Quadra Island and Victoria was set up later; no usable data were recorded.
the earthquake record was chosen for analysis, and group-velocity dispersion calculations were begun. Echo resolution on these data and a lack of ether usable records prevented the continuation of the data processing. No conclusions are drawn about the lithospheric structure; however, recommendations are made regarding possible future experimentation with the existing apparatus. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
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The organization of spiral rainbands in a hurricane.Fung, Inez Yau-Sheung January 1977 (has links)
Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Bibliography : leaves 136-139. / Sc.D.
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Environmental and tectonic systems in Africa and South Asia constrained by seismic noise, surface waves, and scatteringCarchedi, Christopher January 2024 (has links)
In this thesis, I analyze seismic signals collected during two passive-source broadband seismic deployments that instrumented tectonic boundaries with opposing plate motion—the heavily sedimented forearc of the obliquely convergent Indo-Burman subduction zone and the Malawi rift of the divergent East African rift system—as part of the BIMA and SEGMeNT experiments. These two settings provide unprecedented opportunities to broaden the extent of our understanding of tectonic processes and linkages between atmosphere-to-solid earth seismic coupling, respectively. The Indo-Burman forearc represents an extreme endmember system for sedimentary accretion underneath Earth’s largest delta, while the Malawi rift contains one of the widest and deepest freshwater bodies and one of the first to be instrumented by a seismic array from lake bottom to lake shore. Collectively, this work represents a diverse set of seismic observations that improve our understanding of environmental and tectonic systems across a range of scales, from oblique convergence under heavy sedimentation to energy transfer between the atmosphere and the solid earth.
Using the BIMA dataset, we investigate the seismic shear-velocity structure across the extensive sediment blanket, crust, and uppermost mantle of the Indo-Burman forearc margin to robustly constrain subsurface structure and lithology. We construct a comprehensive three- dimensional survey of seismic shear velocity across the region using a joint-inversion of surface- and scattered-wave constraints that explicitly parameterizes key boundary layers. We extract measurements of Rayleigh-wave phase velocities from (1) interstation Rayleigh wavefields produced from the cross-correlation and spectral waveform fitting of ambient seismic noise between 12-25 s period and (2) intra-array Rayleigh-wave phase variations form regional and teleseismic earthquakes propagating across the array between 20-80 s period, in order to constrain absolute shear velocities throughout the model. To constrain the depths to and amplitudes of significant velocity interfaces, we also develop a generalized-Radon-transform migration image across the array and incorporate the resulting scattered-wave measurements into the joint inversion. Together, these measurements complement each other’s individual limitations and allow for a comprehensive modeling analysis.
Overall, the Bengal basin appears markedly slower than other heavily sedimented basins observed globally. East-west dispersion variations highlight a deepening slow structure to the east, which suggests a basin geometry primarily controlled by a down-dipping slab interface as opposed to central basin loading. Scattered-wave imaging captures three important interfaces in the velocity architecture underlying the region. Within the joint-inversion modeling, we observe two model classes that emblemize the evolution of consolidation and stress state within the uppermost sediments and metasediments along a predominantly northeast-southwest trend. We interpret variations in deeper seismic structure under two proposed scenarios: (1) a Moho at ~21-26 km underlying a package of metasediments and a thin oceanic crust, with a slow mantle lithosphere that may contain retained melt from the onset of India-Antarctica seafloor spreading; or (2) a Moho at ~50-59 km underlying a package of metasediments and a thick slug of mafic material, which may correspond to significant underplating from the Kerguelen hotspot at the time of creation of the subducting crust. These findings improve our understanding of sediment evolution and tectonic architecture across the Indo-Burman forearc margin.
Using the amphibious SEGMeNT data at Lake Malawi, we explore variations in the spectral character of lake-generated microseisms to investigate the dominant parameters controlling seismic coupling between water and the solid earth. We document clear evidence for two spectral peaks in the lake microseism band, and relate variations in spectral behavior as a function of recording depth and proximity to steep lake-floor slopes and shorelines to suggest that these spectral bands may correspond to single- and double-frequency generation processes, akin to primary and secondary ocean microseisms. Some observations are otherwise complex and inconsistent with traditional microseism theory, indicating that signals may alternatively reflect interactions between differing source regions within separate basins of the lake under exclusively double-frequency generation processes, an ambiguity that might have been resolved with the availability of colocated wind and wave-state data sets.
This dissertation work highlights the value of array-based seismic deployments and the incorporation of complementary data types for exploring the detailed structure and evolution of systems, especially in high-noise settings.
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Amplification of generalized surface waves.Michalopoulos, Evangelos. January 1976 (has links)
Thesis: M.S., Massachusetts Institute of Technology, Department of Civil Engineering, 1976 / Bibliography: leaf 139. / M.S. / M.S. Massachusetts Institute of Technology, Department of Civil Engineering
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Rayleigh wave scattering across step discontinuitiesNathman, Douglas Robert January 1980 (has links)
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Bibliography: p. 142-149. / by Douglas Robert Nathan. / M.S.
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Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber AnalysisYoon, Sungsoo 20 July 2005 (has links)
Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
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Determinação do Gmáx através do método de análise espectral de ondas superficiais / Determination of GMax using spectral-analysis-of-surface-waves.Flores Apaza, Marco Aurelio . 16 April 2009 (has links)
Esta dissertação apresenta o método de análise espectral de ondas superficiais (SASW) para a obtenção das variações do módulo cisalhante (Gmáx) com a profundidade, no domínio das deformações muito pequenas (abaixo de 0,001%). O SASW é um método sísmico in situ, não destrutivo, baseado na geração e detecção de ondas Rayleigh e na natureza dispersiva desta onda. Pela aplicação de um impacto na superfície do solo e detecção da onda em vários pontos, através de dois receptores, é construída uma curva de dispersão (velocidade de fase versus comprimento de onda). Esta curva de dispersão é, então, invertida. A inversão é um processo analítico para a reconstrução do perfil de velocidade de onda de cisalhamento (VS), partindo-se da curva de dispersão experimental de campo. O módulo de cisalhamento máximo de cada camada é facilmente obtido a partir do perfil de VS. No conteúdo teórico da dissertação discutem-se propriedades dinâmicas dos solos e descrevem-se as equações que dominam a propagação das ondas elásticas, tanto em meios homogêneos como em meios estratificados. A metodologia desenvolvida para a obtenção das curvas de dispersão, através da realização de ensaios SASW, apresenta os resultados obtidos em ensaios realizados na Cidade Universitária em São Paulo, sendo esses resultados comparados com estimativas feitas a partir de correlações baseadas em ensaios SPT existentes. Essas comparações permitem concluir que a metodologia SASW é uma boa alternativa para a determinação do perfil de rigidez (Gmáx) do solo, concordando com o nível de deformação envolvido nos ensaios. São desenvolvidos estudos de sensibilidade do método para verificar a influência na mudança dos parâmetros assumidos (peso específico, coeficiente de Poisson e espessuras das camadas) no processo de redução de dados (inversão) sobre o perfil final de VS, concluindo-se que o parâmetro que apresenta maior influência é o coeficiente de Poisson. / This dissertation presents the spectral-analysis-of-surface-waves (SASW) method as a tool for obtaining the variations in the modulus shear (Gmax) with depth in the field of very small strains (below 0,001%). The SASW method is a nondestructive in situ seismic method, based on the generation and measurement of Rayleigh wave and on its dispersive characteristic nature. Throughout the implementation of an impact on the soil surface and the detection of the wave at various points by two receptors a dispersion curve is constructed (phase velocity versus wave-length). This dispersion curve is then inverted. Inversion is an analytical process for reconstructing the shear wave velocity profile from the experimental field. The shear modulus of each layer is readily obtained from the shear wave velocity profile. The theoretical content of the dissertation presents dynamic properties of the soils and is described in the equations that dominate the propagation of elastic waves, both in homogeneous media and in stratified media. The methodology developed to obtain the dispersion curves through the implementation of SASW test is defined, and results from tests carried out at the University Campus in São Paulo are presented and compared with values obtained from correlations based on SPT tests. These comparisons indicate that the SASW method is a good alternative to determine the profile of stiffness (Gmax) of the soil, agreeing with the level of deformation involved in the tests. Studies on the methods sensitivity are developed to verify the influence on the changing of the parameters given (natural unit weight, Poisson coefficient and thickness of layers) in reduction of data (inversion) on the final profile of VS. The conclusion is that the Poisson coefficient is the parameter with greater influence.
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The 1988 Lancang-Gengma, China, earthquake sequence : teleseismic body wave, surface wave and strong ground motion studiesLi, Xiao-qing, 1963- 06 August 1991 (has links)
On November 6, 1988, two strong earthquakes (Mw: 7.0 and 6.8) separated
by about 13 minutes occurred in Yunnan Province, China. The aftershocks located
by Kunming Telemetered Seismic Network form a lineament approximately 120 km
long and 20 km wide with the long dimension oriented approximately N30°W. The
epicenter of the first event lies about 30 km from the southern terminus of the
aftershock zone while the epicenter of the second event is 60 km further to the
northwest. Field investigations indicate that the surface fault ruptures associated with
the first and second shock and a variety of ground deformations.
We analyze teleseismic data recorded by the GDSN network to determine the
rupture process of these two mainshocks (referred to as Ml and M2) and the two
largest aftershocks (referred to as Al and A2).
Inversion of long-period body waves gives the following centroid source
parameters for Ml: strike 154°±4°, dip 86°±1°, slip 181°±1°, centroid depth shallower
than 15 km (least-misfit centroid depth 12 km), and seismic moment 4.5-4.9 X 10²⁶
dyn cm (least-misfit seismic moment 4.6 X 10²⁶ dyn cm). The source time function,
further constrained by broadband seismograms, indicates that the source duration for
this event is 12 seconds.
Due to signal interference with Ml, body wave inversion techniques cannot
be applied to M2. The Rayleigh waves provide a better look at this event. In order to
identify the energy contributions from the two events, group velocity analysis was
performed on the surface wave trains. The energy from the individual events was
then isolated based on their dispersion patterns. The amplitude spectra in the period
range of 100 to 66 s were inverted for the source parameters. The inversion
constrains the strike of M2 precisely (155°±3°), however, dip and slip angles were
not well resolved by the inversion. Similar Rayleigh wave amplitude spectra and
radiation patterns of Ml and M2, however, suggest that they had very similar
mechanisms and centroid depths. On the average, the amplitude spectra of M2 are
smaller than those of Ml by a factor of 2.2, indicating the seismic moment of M2 is
2.1 X 10²⁶ dyn cm.
The two largest aftershocks, Al (Mw 6.1) and A2 (Mw 5.3), which occurred
at the southern terminus of the aftershock zone, were analyzed by modeling
teleseismic and strong ground motion data. Teleseismic body wave inversion gives
source orientation of Al: strike 165°±2.5°, dip 90°±1.5°, slip 178°±0.5°, centroid
depth shallower than 12 km (least-misfit centroid depth 7 km from broadband
waveform inversion), and seismic moment 1.5-1.6 X 10²⁵ dyn cm. The inversion of
A2 gives the source orientation and centroid depth very similar to those of Al. The
seismic moment for this event is 1.3-1.6 X 10²⁴ dyn cm. Modeling of strong ground
motion seismograms adds more constraints on centroid depths and source time
functions of Al and A2. To minimize the effect of scattering caused by upper crustal
heterogeneity, we confined our analysis to frequencies lower than 1 Hz. A crustal
model, with a low velocity sedimentary layer, was found that predicts common
features of observed strong ground motion seismograms for both events. Derived
source orientation is consistent with that found from teleseismic body wave
inversion. The centroid depths of Al and A2 were constrained to be between 4 and
12 km. A source duration of 7 s and 2 s was obtained for Al and A2, respectively.
Derived rupture parameters of Ml and M2, aftershock distribution, field
investigations, geological information and concepts of geometrical barriers and fault
asperities, indicate that the preexisting fault intersections played the key role in
rupture terminations and initiations. The 12 s source duration of Ml and about 60 km
long zone of ground deformation along the strike suggest that Ml rupture was
bilateral. The rupture initiated near a fault intersection and propagated to NNW and
SSE along the strike. The SSE propagating rupture was terminated by a preexisting
fault which intersects the ruptured fault 30 km to the south. The aftershock Al and
A2 as well as a dense group of small aftershocks were associated with the termination
of the SSE segment. The NNW propagating rupture was also terminated by a NE
striking preexisting fault on which several of the largest aftershocks appear to have
occurred. This NE striking fault right-laterally offsets the fault on which Ml and M2
occurred forming a geometrical barrier for the rupture. M2 presumably nucleated near
this barrier and unilaterally ruptured about 25 km toward NNW where it was
terminated by a well documented preexisting fault. / Graduation date: 1992
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Determination of Longitudinal Stress in RailsDjayaputra, Ferdinand 2010 December 1900 (has links)
The 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.
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