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1
Lo, Tien-when. "Seismic borehole tomography". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/54325.
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Nurhandoko, Bagus Endar Bachtiar. "Fresnel zone seismic tomography". Kyoto University, 2000. http://hdl.handle.net/2433/180954.
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3
Yang, Ting. "Seismic constraints on structure beneath hotspots : earthquake tomography & finite frequency tomography approaches /". View online ; access limited to URI, 2006. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3232466.
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4
Zhang, Qie Sandvol Eric Alan. "Seismic tomography and anisotropy: studies of intraplate seismic zones". Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6855.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Eric Sandvol. Vita. Includes bibliographical references.
5
Lees, Jonathan Matthew. "Seismic tomography in western Washington /". Thesis, Connect to this title online; UW restricted, 1989. http://hdl.handle.net/1773/6829.
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Dyer, Benjamin Charles. "Seismic transmission and reflection tomography". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47042.
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7
Dumont-Kristiansen, Frédéric-Nicolas. "Spatial variability in seismic depth tomography". Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9501.
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The location of a reflector or medium in the subsurface is correlated with the high wavenumbers or high frequencies in the velocity field. Indeed, the determination of the high frequencies of the velocity field both normally and laterally is the key step for improving seimic data and then get a better insight of the position of a reflector in the subsurface. This project focus on the velocity data processing part involved in seismic tomography. We describe, compare and implement several highpass operators based on finite-difference and the Hamming window in order to filter a seismic velocity dataset. In fact, we study their behaviour in the frequency domain by examining their spectrums. The main contribution of this project is to construct two dimensional anisotropic operators by rotating a one dimensional operator based on linear interpolation. We test all the operators on a synthetic seismic velocity dataset and compare the results obtained between the isotropic filtering method and the anisotropic filtering method. We show that anisotropic filters can be useful in certain geological circumstances. Finally we attempt to scale the different operators in order to fully incorporate them in the seismic tomography inversion problem by using a Bayesian method. We show that it is possible to decide the strength of the constraint in which we want to filter the seismic dataset by using a regularization parameter.
8
Gruber, Thomas. "Crosshole seismic tomography incorporating later arrivals /". Title page, contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phg885.pdf.
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9
Galetti, Erica. "Seismic interferometry and non-linear tomography". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10506.
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Seismic records contain information that allows geoscientists to make inferences about the structure and properties of the Earth’s interior. Traditionally, seismic imaging and tomography methods require wavefields to be generated and recorded by identifiable sources and receivers, and use these directly-recorded signals to create models of the Earth’s subsurface. However, in recent years the method of seismic interferometry has revolutionised earthquake seismology by allowing unrecorded signals between pairs of receivers, pairs of sources, and source-receiver pairs to be constructed as Green’s functions using either cross-correlation, convolution or deconvolution of wavefields. In all of these formulations, seismic energy is recorded and emitted by surrounding boundaries of receivers and sources, which need not be active and impulsive but may even constitute continuous, naturally-occurring seismic ambient noise. In the first part of this thesis, I provide a comprehensive overview of seismic interferometry, its background theory, and examples of its application. I then test the theory and evaluate the effects of approximations that are commonly made when the interferometric formulae are applied to real datasets. Since errors resulting from some approximations can be subtle, these tests must be performed using almost error-free synthetic data produced with an exact waveform modelling method. To make such tests challenging the method and associated code must be applicable to multiply-scattering media. I developed such a modelling code specifically for interferometric tests and applications. Since virtually no errors are introduced into the results from modelling, any difference between the true and interferometric waveforms can safely be attributed to specific origins in interferometric theory. I show that this is not possible when using other, previously available methods: for example, the errors introduced into waveforms synthesised by finite-difference methods due to the modelling method itself, are larger than the errors incurred due to some (still significant) interferometric approximations; hence that modelling method can not be used to test these commonly-applied approximations. I then discuss the ability of interferometry to redatum seismic energy in both space and time, allowing virtual seismograms to be constructed at new locations where receivers may not have been present at the time of occurrence of the associated seismic source. I present the first successful application of this method to real datasets at multiple length scales. Although the results are restricted to limited bandwidths, this study demonstrates that the technique is a powerful tool in seismologists’ arsenal, paving the way for a new type of ‘retrospective’ seismology where sensors may be installed at any desired location at any time, and recordings of seismic events occurring at any other time can be constructed retrospectively – even long after their energy has dissipated. Within crustal seismology, a very common application of seismic interferometry is ambient-noise tomography (ANT). ANT is an Earth imaging method which makes use of inter-station Green’s functions constructed from cross-correlation of seismic ambient noise records. It is particularly useful in seismically quiescent areas where traditional tomography methods that rely on local earthquake sources would fail to produce interpretable results due to the lack of available data. Once constructed, interferometric Green’s functions can be analysed using standard waveform analysis techniques, and inverted for subsurface structure using more or less traditional imaging methods. In the second part of this thesis, I discuss the development and implementation of a fully non-linear inversion method which I use to perform Love-wave ANT across the British Isles. Full non-linearity is achieved by allowing both raypaths and model parametrisation to vary freely during inversion in Bayesian, Markov chain Monte Carlo tomography, the first time that this has been attempted. Since the inversion produces not only one, but a large ensemble of models, all of which fit the data to within the noise level, statistical moments of different order such as the mean or average model, or the standard deviation of seismic velocity structures across the ensemble, may be calculated: while the ensemble average map provides a smooth representation of the velocity field, a measure of model uncertainty can be obtained from the standard deviation map. In a number of real-data and synthetic examples, I show that the combination of variable raypaths and model parametrisation is key to the emergence of previously-unobserved, loop-like uncertainty topologies in the standard deviation maps. These uncertainty loops surround low- or high-velocity anomalies. They indicate that, while the velocity of each anomaly may be fairly well reconstructed, its exact location and size tend to remain uncertain; loops parametrise this location uncertainty, and hence constitute a fully non-linearised, Bayesian measure of spatial resolution. The uncertainty in anomaly location is shown to be due mainly to the location of the raypaths that were used to constrain the anomaly also only being known approximately. The emergence of loops is therefore related to the variation in raypaths with velocity structure, and hence to 2nd and higher order wave-physics. Thus, loops can only be observed using non-linear inversion methods such as the one described herein, explaining why these topologies have never been observed previously. I then present the results of fully non-linearised Love-wave group-velocity tomography of the British Isles in different frequency bands. At all of the analysed periods, the group-velocity maps show a good correlation with known geology of the region, and also robustly detect novel features. The shear-velocity structure with depth across the Irish Sea sedimentary basin is then investigated by inverting the Love-wave group-velocity maps, again fully non-linearly using Markov chain Monte Carlo inversion, showing an approximate depth to basement of 5 km. Finally, I discuss the advantages and current limitations of the fully non-linear tomography method implemented in this project, and provide guidelines and suggestions for its improvement.
10
Trinks, Immo. "Traveltime tomography of densely sampled seismic data". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615782.
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11
Ivansson, Sven. "Applications of seismic tomography to geophysical exploration". Licentiate thesis, Luleå tekniska universitet, 1987. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26497.
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12
Loveday, David Carl. "Resolving Small Objects Using Seismic Traveltime Tomography". Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/35032.
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It is often claimed that the first Fresnel zone associated with the dominant frequency represents the spatial resolution limit of traveltime tomography. We show, however, that the relevant Fresnel limit for tomographic resolution is the maximum, not the dominant frequency in the data. For physically realizable causal wavelets, the maximum frequency is infinite. In practice, noise lowers the effective possible maximum frequency. To demonstrate these points, synthetic seismic data were generated for traveltime picking and inversion for a single, small velocity anomaly embedded in a homogeneous background velocity. A variety of traveltime picking techniques were tested and compared for their ability to detect the presence of objects smaller than that Fresnel zone associated with the dominant frequency. All methods produced accurate ray-theoretical (infinite-frequency) picks from noise-free seismic data for objects smaller than the dominant-frequency Fresnel zone. For the lowest dominant frequencies with Fresnel zones many times larger than the object, picking methods that focus on features along the onset of the first arrival were the most accurate, while cross-correlation with a known wavelet preformed less accurately. First-onset picking methods perform better because they take advantage of the highest frequencies in the data, whereas the correlation wavelet is typically in line with the dominant frequency. All methods successfully detected the presence of objects smaller than a wavelength. The inversion of the traveltime picks from the different picking methods always recovered the position and shape of the object. Random noise at a range of signal-to-noise ratios was then added to the seismic data and the data were repicked. Pick times with different noise realizations are statistically centered on the noise-free pick, not the time that would be recorded in the absence of the object. Trace stacking prior to picking or the averaging of many picks improves the signal-to-noise ratio and can extract signal that is not detected on an individual pick. An averaging of traveltime picks also occurs during tomographic inversion. This inherent signal-to-noise improvement allows tomography to image objects that are undetectable in individual trace picks. The resolution of tomography is limited not by the Fresnel zone associated with the dominant frequency, but by the accuracy of the traveltime picks. Resolution is further improved by dense ray coverage.Master of Science
13
McCaughey, Michael. "Travel-time tomography of wide-angle seismic data". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389868.
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14
Foss, Stig-Kyrre. "Depth consistent pp and ps seismic angle tomography". Doctoral thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-318.
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This thesis addressed the problem of finding background models yielding depth consistent migrated PP and PS images, i.e. geologically equivalent reflectors should be imaged at the same depth in the two images. The tomographic approach in search of a background medium, is performed as a combination of migration velocity analysis by differential semblance in angle and map migration. A practical strategy for obtaining estimates of all parameter values in a transversely isotropic medium with a known symmetry axis is presented. The approach combines the search of a background medium yielding optimum focusing ability by differential semblance and the matching of PP and PS key reflectors in depth by means of map migration. This can also be used to match the imaged reflectors with known depths e.g. from well markers.
For the purpose of fast and computationally inexpensive imaging and tomography in angle, a complete review and analysis for the 2.5-D case is performed. The theory is also extended to anisotropic media under necessary and sufficient assumptions. An analysis is performed with regards to parameter issues in 2.5-D in anisotropic media. All inversion and migration results are derived in the natural coordinate system, namely scattering/reflection angle at the imaging point by means of the generalized Radon transform.
15
Hope, Victoria. "Applications of seismic transmission tomography in civil engineering". Thesis, University of Surrey, 1993. http://epubs.surrey.ac.uk/842729/.
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The principles of tomography are well-established, and geotomography has been in use for several decades. Seismic tomography has previously been used principally in the oil and nuclear industries, but it has occasionally been applied in civil engineering site investigation (SI). The technique can provide a qualitative or a quantitative representation of the distribution of the seismic velocity properties within a surveyed region. Seismic tomography has been successfully used to image, for example, zones of fracturing. The technique has been less successful when used to detect cavities. This thesis presents a theoretical and experimental examination of the usefulness - or otherwise - of seismic tomography in SI. It is found that geotomography has a role to play when one is interested in, for example, general subsurface variability. An explanation is offered for the low success rate of cavity detection surveys utilizing seismic velocity tomography. It is shown that, of the numerous and diverse fields of application of the tomographic method, geotomography offers what is, perhaps, the most inherently ill-posed form of the reconstruction problem. Significant difficulties are encountered because, in general, measurements can be acquired from only a restricted set of positions. Additional problems are introduced through the use of seismic wave energy, which follows hard-to-predict routes across the surveyed zone. Observational errors lead to inconsistencies within a tomographic system. In consequence, the geotomographic reconstruction problem is typically under-determined, inconsistent and non-linear. An heuristic method of reconstructing seismic velocity tomograms from typical field data is developed and presented.
16
Rao, Ying. "Seismic tomography for velocity and attenuation model reconstruction". Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/11882.
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17
Tape, Carl Clayton Robert W. Tromp Jeroen. "Seismic tomography of Southern California using adjoint methods /". Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-05062009-183823.
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18
Carannante, Simona <1976>. "Multiresolution spherical wavelet analysis in global seismic tomography". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/871/1/Tesi_Carannante_Simona.pdf.
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Every seismic event produces seismic waves which travel throughout the Earth.
Seismology is the science of interpreting measurements to derive information about the structure of the
Earth. Seismic tomography is the most powerful tool for determination of 3D structure of deep Earth's
interiors. Tomographic models obtained at the global and regional scales are an underlying tool for
determination of geodynamical state of the Earth, showing evident correlation with other geophysical and
geological characteristics. The global tomographic images of the Earth can be written as a linear
combinations of basis functions from a specifically chosen set, defining the model parameterization. A
number of different parameterizations are commonly seen in literature: seismic velocities in the Earth
have been expressed, for example, as combinations of spherical harmonics or by means of the simpler
characteristic functions of discrete cells.
With this work we are interested to focus our attention on this aspect, evaluating a new type of
parameterization, performed by means of wavelet functions. It is known from the classical Fourier theory
that a signal can be expressed as the sum of a, possibly infinite, series of sines and cosines. This sum is
often referred as a Fourier expansion. The big disadvantage of a Fourier expansion is that it has only
frequency resolution and no time resolution.
The Wavelet Analysis (or Wavelet Transform) is probably the most recent solution to overcome the
shortcomings of Fourier analysis. The fundamental idea behind this innovative analysis is to study signal
according to scale. Wavelets, in fact, are mathematical functions that cut up data into different frequency
components, and then study each component with resolution matched to its scale, so they are especially
useful in the analysis of non stationary process that contains multi-scale features, discontinuities and
sharp strike. Wavelets are essentially used in two ways when they are applied in geophysical process or
signals studies: 1) as a basis for representation or characterization of process; 2) as an integration kernel
for analysis to extract information about the process.
These two types of applications of wavelets in geophysical field, are object of study of this work.
At the beginning we use the wavelets as basis to represent and resolve the Tomographic Inverse
Problem. After a briefly introduction to seismic tomography theory, we assess the power of wavelet
analysis in the representation of two different type of synthetic models; then we apply it to real data,
obtaining surface wave phase velocity maps and evaluating its abilities by means of comparison with an
other type of parametrization (i.e., block parametrization).
For the second type of wavelet application we analyze the ability of Continuous Wavelet Transform
in the spectral analysis, starting again with some synthetic tests to evaluate its sensibility and capability
and then apply the same analysis to real data to obtain Local Correlation Maps between different model
at same depth or between different profiles of the same model.
19
Carannante, Simona <1976>. "Multiresolution spherical wavelet analysis in global seismic tomography". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/871/.
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Every seismic event produces seismic waves which travel throughout the Earth.
Seismology is the science of interpreting measurements to derive information about the structure of the
Earth. Seismic tomography is the most powerful tool for determination of 3D structure of deep Earth's
interiors. Tomographic models obtained at the global and regional scales are an underlying tool for
determination of geodynamical state of the Earth, showing evident correlation with other geophysical and
geological characteristics. The global tomographic images of the Earth can be written as a linear
combinations of basis functions from a specifically chosen set, defining the model parameterization. A
number of different parameterizations are commonly seen in literature: seismic velocities in the Earth
have been expressed, for example, as combinations of spherical harmonics or by means of the simpler
characteristic functions of discrete cells.
With this work we are interested to focus our attention on this aspect, evaluating a new type of
parameterization, performed by means of wavelet functions. It is known from the classical Fourier theory
that a signal can be expressed as the sum of a, possibly infinite, series of sines and cosines. This sum is
often referred as a Fourier expansion. The big disadvantage of a Fourier expansion is that it has only
frequency resolution and no time resolution.
The Wavelet Analysis (or Wavelet Transform) is probably the most recent solution to overcome the
shortcomings of Fourier analysis. The fundamental idea behind this innovative analysis is to study signal
according to scale. Wavelets, in fact, are mathematical functions that cut up data into different frequency
components, and then study each component with resolution matched to its scale, so they are especially
useful in the analysis of non stationary process that contains multi-scale features, discontinuities and
sharp strike. Wavelets are essentially used in two ways when they are applied in geophysical process or
signals studies: 1) as a basis for representation or characterization of process; 2) as an integration kernel
for analysis to extract information about the process.
These two types of applications of wavelets in geophysical field, are object of study of this work.
At the beginning we use the wavelets as basis to represent and resolve the Tomographic Inverse
Problem. After a briefly introduction to seismic tomography theory, we assess the power of wavelet
analysis in the representation of two different type of synthetic models; then we apply it to real data,
obtaining surface wave phase velocity maps and evaluating its abilities by means of comparison with an
other type of parametrization (i.e., block parametrization).
For the second type of wavelet application we analyze the ability of Continuous Wavelet Transform
in the spectral analysis, starting again with some synthetic tests to evaluate its sensibility and capability
and then apply the same analysis to real data to obtain Local Correlation Maps between different model
at same depth or between different profiles of the same model.
20
Legovini, Paride <1983>. "Ambient seismic noise tomography of the Antarctic continent". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amsdottorato.unibo.it/9023/1/tesi-legovini.pdf.
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The lithosphere of Antarctica reacts to both the stress variations due to the dynamics of the mantle and the variation of the glacial load due to changes in climate. These two factors act on the dynamics of the glacial mass, on the evolution of the continent's topography and on the plate seismicity. This means that the knowledge of spatial variations in lithospheric thickness is needed to comprehend of the processes that involve interactions between climate and the geosphere. The main aim of this work is to produce a tomographic model of the continent.
The classic data source for tomographic studies is a set of seismic signals produced by earthquakes. In this work I use a different technique: information is extracted by correlating the ambient seismic noise recorded in different locations. Instead of a the classic cross-correlation, this work uses the phase cross correlation technique, which appears to be more robust in our use case. Signal phases are used even to improve the correlogram stacks, by weighting the stack samples according to the correlograms' coherence.
In Antarctica, the 30s Rayleigh wave group velocity map shows lower velocities in East Antarctica, and higher velocities in West Antarctica, coherently with expectations related to a thicker cratonic crust in the East, and thinner extending crust in the West. Deeper sensitivity of longer periods make the color pattern switch for the 80s map, sensing the upper mantle and consequently higher velocity at the cold roots of cratonic East Antarctica and lower velocity in the tectonically active West.
I also contributed to the maintenance and development of the seismic observational infrastructure in Antarctica. This thesis recaps the activities I carried out during my participation to the 31st campaign of the Italian National Antarctic Research Program, to which I participated during the PhD course.
21
Ellis, Grant Andrew. "Subsurface electromagnetic sensing in the presence of the air-earth interface using a cross-borehole configuration /". Thesis, Connect to this title online; UW restricted, 1995. http://hdl.handle.net/1773/6058.
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22
Chan, Ne Xun. "One- and Three-dimensional P- and S-wave Velocity Models of Central and Southern Sweden Based on SNSN Data". Thesis, Uppsala universitet, Geofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-231929.
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The velocity structures of southern and central part of Sweden have been derived with the local tomography (LET) method. The region has been divided into two study areas and the datasets come from the P- and S-wave traveltimes recorded by the Swedish National Seismic Network (SNSN). Man-made explosions and earthquakes occurring over the period of 5 years and 10 years, respectively, within the study areas have been used. One-dimensional starting models were derived based on an a priori model obtained from the SNSN, that were later used for starting models in the inversion for the 3-D crustal structures of the study areas. Attempts were also made to invert for Moho topography in the areas. The study areas are found to have an upper-crustal thickness of approximately 20 to 25 km and the Moho boundaries vary from 42 to 46 km in depth. The Vp/Vs ratios varies from about 1.68 to 1.78. The LET method appear to resolve the different between the Sveconorgwegian and Svecofennian orogen regions, but the stations and sources are too sparsely distributed for higher resolution models. The seismicity in the study areas are distributed in two distinctive depth ranges. The focal depth of the SNSN catalogued earthquakes concentrated in approximately 5 km and 15 - 20 km depth. Relocations of the earthquakes using a global search method reduced this tendency. The results also show that using 3-D models produces less biased results than using 1-D models with the same relocation method.
23
Ghaychi, Afrouz Setareh. "Seismic Wave Velocity Variations in Deep Hard Rock Underground Mines by Passive Seismic Tomography". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97890.
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Mining engineers are tasked with ensuring that underground mining operations be both safe and efficiently productive. Induced stress in deep mines has a significant role in the stability of the underground mines and hence the safety of the mining workplace because the behavior of the rock mass associated with mining-induced seismicity is poorly-understood. Passive seismic tomography is a tool with which the performance of a rock mass can be monitored in a timely manner. Using the tool of passive seismic tomography, the advance rate of operation and mining designs can be updated considering the induced stress level in the abutting rock. Most of our current understanding of rock mass behavior associated with mining-induced seismicity comes from numerical modeling and a limited set of case studies. Therefore, it is critical to continuously monitor the rock mass performance under induced stress. Underground stress changes directly influence the seismic wave velocity of the rock mass, which can be measured by passive seismic tomography. The precise rock mass seismicity can be modeled based on the data recorded by seismic sensors such as geophones of an in-mine microseismic system. The seismic velocity of rock mass, which refers to the propagated P-wave velocity, varies associated with the occurrence of major seismic events (defined as having a local moment magnitude between 2 to 4). Seismic velocity changes in affected areas can be measured before and after a major seismic event in order to determine the highly stressed zones. This study evaluates the seismic velocity trends associated with five major seismic events with moment magnitude of 1.4 at a deep narrow-vein mine in order to recognize reasonable patterns correlated to induced stress redistribution. This pattern may allow recognizing areas and times which are prone to occurrence of a major seismic event and helpful in taking appropriate actions in order to mitigate the risk such as evacuation of the area in abrupt cases and changing the aggressive mine plans in gradual cases. In other words, the high stress zones can be distinguished at their early stage and correspondingly optimizing the mining practices to prevent progression of high stress zones which can be ended to a rock failure. For this purpose a block cave mine was synthetically modeled and numerically analyzed in order to evaluate the capability of the passive seismic tomography in determining the induced stress changes through seismic velocity measurement in block cave mines. Next the same method is used for a narrow vein mine as a case study to determine the velocity patterns corresponding to each major seismic event.Doctor of Philosophy
Mining activities unbalance the stress distribution underground, which is called mining induced stress. The stability of the underground mines is jeopardized due to accumulation of induced stress thus it is critical for the safety of the miners to prevent excessive induced stress accumulation. Hence it is important to continuously monitor the rock mass performance under the induced stress which can form cracks or slide along the existing discontinuities in rock mass. Cracking or sliding releases energy as the source of the seismic wave propagation in underground rocks, known as a seismic event. The velocity of seismic wave propagation can be recorded and monitored by installing seismic sensors such as geophones underground. The seismic events are similar to earthquakes but on a much smaller scale. The strength of seismic events is measured on a scale of moment magnitude. The strongest earthquakes in the world are around magnitude 9, most destructive earthquakes are magnitude 7 or higher, and earthquakes below magnitude 5 generally do not cause significant damage. The moment magnitude of mining induced seismic events is typically less than 3. In order to monitor mining induced stress variations, the propagated seismic wave velocity in rock mass is measured by a series of mathematical computations on recorded seismic waves called passive seismic tomography, which is similar to the medical CT-scan machine. Seismic wave velocity is like the velocity of the vibrating particles of rock due to the released energy from a seismic event. This study proposes to investigate trends of seismic velocity variations before and after each seismic event. The areas which are highly stressed have higher seismic velocities compared to the average seismic velocity of the entire area. Therefore, early recognition of highly stressed zones, based on the seismic velocity amount prior the occurrence of major seismic events, will be helpful to apply optimization of mining practices to prevent progression of high stress zones which can be ended to rock failures. For this purpose, time-dependent seismic velocity of a synthetic mine was compared to its stress numerically. Then, the seismic data of a narrow vein mine is evaluated to determine the seismic velocity trends prior to the occurrence of at least five major seismic events as the case study.
24
Papaleo, Elvira. "The north Anatolian fault, Turkey : insights from seismic tomography". Thesis, University of Aberdeen, 2018. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=239855.
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The North Anatolian Fault Zone (NAFZ) in Turkey is a major continental strike-slip fault, 1200 km long and with a current slip rate of 25 mm/yr. Historical records show that the NAFZ is capable of producing high-magnitude earthquakes, activating different segments of the fault in a westward progression. Currently, the NAFZ poses a major seismic hazard for the city of Istanbul, which is situated close to one of the two strands into which the fault splays in northwestern Turkey. Understanding of fault zone structure and properties at depth is essential to constrain where deformation occurs within the lithosphere and how strain localises with depth. In fact, geodynamic models explaining surface deformation require knowledge of the width and depth extent of the fault zone in both the crust and upper mantle. In this framework, this thesis aims to provide better constraints on fault zone geometry within the lithosphere. To achieve this objective P and S wave teleseismic tomography have been applied to the data recorded by a dense array of broadband seismic stations (DANA, Dense Array for Northern Anatolia); through teleseismic tomography it was possible to image the NAFZ structure in both the crust and uppermost mantle. In addition, joint inversion i of P-wave teleseismic data and local earthquake data collected using the same array provided a greatly improved resolution within the upper 20 km of the crust. Results from this work highlighted the presence of a shear zone associated to the northern branch of the NAFZ in the study area. The fault zone appears to be 15 km wide within the upper crust and narrows to < 10 km within the lower crust and to Moho depth. In the uppermost mantle its width is constrained to be 30 to 50 km.
25
Lu, Jing S. M. Massachusetts Institute of Technology. "Seismic tomography and surface deformation in Krýsuvík, SW Iceland". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/87506.
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Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 59-62).
The Krýsuvík region of southwestern Iceland is a region of high potential for geothermal energy that is currently experiencing seismic swarm activity and active surface deformation. Understanding the subsurface structure of the area is of great scientific and practical significance. Using permanent and temporary seismic stations deployed in the region, we captured an earthquake swarm from Nov. 2010 to Feb. 2011 clustered around the center of the Krýsuvík volcanic system. We studied the seismicity and Vp, Vs and Vp/Vs ratio in this region by applying double difference tomography. Our tomography result indicates a low velocity zone at a depth of about 6 kin, directly beneath the earthquake swarm. At the same time, our relocation result delineates strike-slip and dip-slip faults above and around this low velocity zone. Brittle-ductile transition is delineated based on the distribution of the earthquakes in this area. In order to understand the relation between the subsurface structure and the surface deformation, we modeled surface deformation using the input parameters constrained from our tomography results. We found that the main deformation is well captured by a pressure source yielding a volume expansion of about 30x 106 m3 at the depth of about 6 km, centered on the low velocity zone detected in tomography. And the secondary deformation could be explained by the normal and the right-lateral slip faults, whose patterns are delineated by the earthquake relocations. The combination of the local stress caused by the expanding source and regional stress that yields a combination of left-lateral shear and extension might have triggered the earthquakes. Based on the low Vp, Vs and possibly high Vp/Vs ratio at depth of ~6 km and its expanding property, the possibilities of supercritical water, H₂O-rich partial melting with magma intrusion are discussed. The results of this thesis provide new insights to understand the seismicity and surface deformation in volcanic zones as well as provided important reference in exploration of new geothermal areas.
by Jing Liu.
S.M. in Geophysics
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Hosa, Aleksandra M. "Imaging of the Hellenic subduction zone by seismic tomography". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/114344.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 24-25).
The Hellenic subduction zone is a complicated tectonic boundary, along which transitions in the nature of subducted material are believed to occur. The objective of this study was to better constrain the subsurface geometry of the Hellenic subduction zone by increasing the resolution of an existing tomographic model of the region. Increase in resolution is important for understanding the effects of inferred transitions in subducted material at depth. Nonlinear inversion of P-wave travel times was used on a global dataset expanded by temporary array data collected in southern Greece. Results show a vertically continuous slab, with a break at the depth 200-400 km detected only in the NW portion of the system. At depth above 400 kin, there is a lateral discontinuity marked by the Central Hellenic Shear Zone and Kephalonia Transform Fault, with slab more pronounced in southern part of the system. Our study supports the hypothesis of the change in subduction mode between northern and southern part of Hellenic arc in late Pliocene.
by Aleksandra M. Hosa.
S.B.
27
Mohamadian, Sarvandani Mohamadhasan. "Seismic tomography of an amagmatic ultra-slow spreading ridge". Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS467.
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Les dorsales ultra-lentes quasi-amagmatiques constituent une nouvelle catégorie de dorsales océaniques caractérisées par une accrétion crustale, exposant sur le fond marin des quantités considérables de péridotites provenant du manteau. L’étude de la contribution des processus tectoniques, magmatiques et d’autres processus impliqués est nécessaire pour obtenir un modèle conceptuel complet des dorsales océaniques à accrétion ultra-lente. L’imagerie des structures de la croûte et du manteau supérieur peut nous aider à comprendre les activités géologiques passées et actuelles sur les dorsales à accrétion océanique ultra-lente. L’objectif du projet est de comprendre la croûte océanique formée dans une dorsale à accrétion ultra-lente appelée ride sud-ouest indienne, à faible apport de magma. Notre projet de recherche est basé sur le traitement et la modélisation de données sismiques actives et passives dans la partie la plus orientale de la dorsale Sud-Ouest Indienne. L’acquisition des données géophysiques a eu lieu en 2014 lors de la campagne SISMOSMOOTH, à bord du N/O Marion-Dufresne. Nous avons analysé les enregistrements des composantes verticales de 43 sismomètres fond de mer (OBS) dans notre approche sismique passive et les composantes hydrophones de 16 sismomètres fond de mer pour l’approche sismique active. L’interférométrie de bruit ambiant et l’inversion de forme d’onde complète (FWI) des données de réfraction ont été utilisées pour imager les structures internes de la croûte et de la lithosphère. Grâce à la modélisation de l’interférométrie de bruit ambiant, on trouve une épaisseur moyenne de croûte de 7 km avec une couche peu profonde de faibles vitesses de cisaillement. De plus, nous en déduisons que les 2 km supérieurs sont très poreux et peuvent être fortement serpentinisés. La vitesse moyenne des ondes de cisaillement entre la base de la croûte et la profondeur maximale de notre modèle (15 km) est inférieure à la valeur de référence globale de 4.5 km/s et peut s’expliquer par le jeune âge des fonds marins de notre zone. Notre modèle bi-dimensionnel de vitesse des ondes P obtenu à partir de notre analyse FWI suggère des variations considérables de composition dans la partie supérieure le long du profil parallèle à l’axe. Notre étude propose un domaine de transition entre un domaine à prédominance volcanique et un non magmatique, entre ∼65 à 95 km de distance sur le profil. Des injections magmatiques dans des dikes sont proposées dans le domaine oriental non volcanique. Une augmentation vers l’ouest de l’apport de matériel magmatique est confirmée pour le mode d’accrétion océanique. Le modèle de vitesse des ondes P associé aux variations de serpentinisation suggère que le Moho est une transition graduelle d’une péridotite hydratéevers une péridotite non altéréeUltra-slow spreading ridges are a new category of spreading ridges characterized by quasi-amagmatic crustal accretion, exposing considerable amounts of mantle derived peridotites on the seafloor. Investigating the contributions of tectonic, magmatic, and other involved processes is necessary to gain a comprehensive conceptual model of ultra-slow spreading ridges. Imaging the crustal and upper mantle structures can help us to understand the past and current geological activities in the ultra-slow spreading ridges. The aim of the project is to understand the oceanic crust formed in an ultra-slow spreading ridge called the Southwest Indian Ridge with a low melt supply. Our research project is based on the processing and modeling of the active and passive seismic data in the easternmost part of Southwest Indian Ridge. The data acquisition took place in 2014 during the SISMOSMOOTH cruise. We analyzed vertical component recordings from 43 ocean-bottom seismometers in our passive seismic approach and the hydrophone components of 16 ocean-bottom seismometers in the active seismic approach. Ambient-noise interferometry and full-waveform inversion (FWI) of refraction data were used to image the internal structures of the lithosphere. In the modeling of ambient-noise interferometry, we find an average crustal thickness of 7 km with a shallow layer of low shear velocities. Moreover, we infer that the uppermost 2 km are highly porous and may be strongly serpentinized. The average shear wave velocity between the base of the crust and the maximum depth of our model (15 km) was less than the global reference value of 4.5 km/s and was explained by the younger age of the seafloor in our area. Our two-dimensional P-wave velocity model obtained from FWI suggests considerable variations in the upper lithospheric compositions along the axis-parallel profile. A transition is expected at a distance of ∼65-95 km along the profile from the predominantly volcanic domain in the western zone to variable serpentinized peridotite in the eastern zone. Dike injections are predicted in this area. A westward increase in melt supply is proposed in the seafloor accretion mode. The serpentinization and P-wave velocity model suggests that the Moho is a gradual transition from hydrated to unaltered peridotite
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Ecoublet, Philippe. "Bent-ray travel-time tomography and migration without ray tracing". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263006.
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Furniss, Matthew David. "Quantitative Comparison of Seismic Velocity Tomography With Seismic Activity Around a Deep Coal Longwall Panel". Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/32659.
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Mining induced seismicity can lead to bumps which cause problems at many mines within the United States and around the world. This seismicity, often referred to as bumps or bursts, can result in injuries, fatalities, and expensive capital damage and production interruptions. There are many factors that contribute to mining induced seismicity but there is still no concrete method to forecast future seismic activity around a mine.
One of the main precursors to large seismic events is an increase in situ stress. One way to find areas within geological strata that are highly stressed is to measure p-wave propagation velocities. High p-wave propagation velocities are associated with high in-situ stress levels. By using tomography programs a three-dimensional velocity model can be constructed. When seismic activity is present the event arrival times at each geophone, the locations of each geophone, and the three dimensional velocity model are used in conjunction with one another to locate the seismic events.
This research compares the locations of seismic events from a deep coal mine longwall panel in the western United States with the associated p-wave propagation velocities from the previous 24 hours. The aim of this comparison is to provide a link between high velocities and seismic activity that could potentially be used to forecast future seismic activity. The comparison is completed both qualitatively through the use of a visual analysis, and quantitatively using various numerical and correlation comparisons on the seismic and velocity data. The qualitative comparison is completed using the event locations from the tomography program SIMULPS. The quantitative comparison is completed twice using two different tomography programs, SIMULPS and TomoDD, which use different methods for locating the seismic events.
Before these comparisons were completed the stresses around the longwall panel were first modeled using the boundary element modeling program LAMODEL to study the effects of three backfilled cross panel entries which were located ahead of the mining face. The modeling showed similar vertical stress distributions as a panel without cross panel entries but higher stress magnitudes.
The qualitative analysis involved comparing tomograms created with SIMULPS with seismicity plots from the following day. One noticeable feature of these tomograms is the presence of a stressed area directly ahead of the face. This stressed area represents the forward abutment. The results of this qualitative analysis illustrate a correlation between high p-wave velocities and seismic activity 24 hours later for several of the days studied. The other days showed little to no correlation. Additionally, not all high p-wave velocity regions resulted in seismic activity. Due to these inconsistencies visually analyzing velocity plots obtained from the program SIMULPS is not a reliable way to forecast the locations of seismic activity 24 hours later.
The result of the quantitative comparisons completed with the programs SIMULPS and TomoDD further highlighted inconsistencies in the correlation between high p-wave velocities and associated seismic activity 24 hours later. TomoDD provided better correlation values than SIMULPS and generally showed that as the level of seismicity increased the p-wave propagation velocities 24 hours prior also increased. Although TomoDD provided good correlations for some of the data pairs studied, the overall inconsistencies prompt the need for further study in this area using TomoDD to find the optimal forecasting time period.Master of Science
30
Muchaidze, Iana. "Imaging in karst terrain using electrical resistivity tomography". Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Muchaidze_09007dcc80534d1b.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 26, 2008) Includes bibliographical references (p. 66-67).
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Whiting, Peter Mark. "Reflection traveltime tomography and the maximum entropy principle". Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26623.
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Conventional reflection tomography creates an estimate of subsurface seismic velocity structure by inverting a set of seismic traveltime data. This is achieved by solving a least-squares optimisation problem that finds the velocity and depth model that minimises the difference between raytraced and measured traveltimes. Obtaining the traveltime data can be difficult as manual picking of reflection times is required and all picked reflection events must be associated with the reflector depths defined in the model. Even with good traveltime data the optimisation problem is very non-linear and the surface restriction of the sources and receivers makes the problem generally underdetermined. These issues result in severe ambiguity and local minima problems.
This thesis shows that modifications to the conventional reflection tomography algorithm can make it a more practical and reliable procedure that is less likely to be trapped by local minima. The ray tracing procedure is changed so that reflector depths are not necessary and automatic traveltime interpretation can be successful. Entropy constraints are introduced (after being justified) which prevent unwarranted velocity structure from appearing. This feature adds significant stability and reduces the ambiguity problems. Staged smoothing of the optimisation function helps avoid local minima.
Synthetic data examples show that the algorithm can be very effective on noise free data. Adding noise to synthetic data reduces the algorithms effectiveness, but inversions of real data sets produces updated velocity fields that result in superior pre-stack depth migrations.
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Symons, Neill. "Seismic velocity structure of the Puget Sound Region from 3-D non-linear tomography /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6813.
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Herwanger, Jorg. "Seismic and electric crosshole tomography for fracture detection and characterization". Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367577.
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Valentine, Andrew P. "Imaging the Earth : Methods and algorithms for global seismic tomography". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533890.
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Robertson, Graham Scott. "Shear wave heterogeneity in the lower mantle from seismic tomography". Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:99ea6162-a1d5-4544-8f52-8deed81d065f.
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To date, most shear velocity heterogeneity models in the lower mantle have been derived using long period data. Comparatively little use has been made of the vast ISC database of shear wave arrival times, which covers the years 1964 to 1991. The aim of this study is to use this database to construct global models of shear wave heterogeneity in the lower mantle and compare it with existing P models using similar period data in order to evaluate the hypothesis that P and S heterogeneity are proportional. In order to reproduce the resolution operator inherent in these existing models, the same parameterization has been employed; lateral dependence is in terms of spherical harmonics up to degree and order 6, and radial dependence in terms of a quartic polynomial. The inversion uses data from over 4500 events selected according to criteria which minimize the bias introduced by uneven source receiver coverage. Despite having approximately one sixth of the amount of data the model correlates well with a P wave model computed using data from the same events, and this in turn is almost identical to models computed by other authors using similar inversion methods. Assuming proportionality of P and S heterogeneity, a joint inversion of the P and S data has been performed. The resultant model correlates extremely well with the P model of this study, and similar variance reductions are obtained for both the P and S datasets as were found in the original inversions. Several model parameterizations have been used to try to investigate the dependence of the model expansion on the results. Consequently, taking into account results from synthetic experiments and from experiments into trade-offs with other inversion parameters, the average ratio of relative S to P heterogeneity d ln vsandfrasl;d ln vp throughout the lower mantle is constrained to be in the interval (1.8,2.1) with emphasis on higher values within these bounds. This value is in agreement with other studies using similar period data, and the upper bound is close to the optimum value of 2.27 obtained by Li et al., 1991 from normal mode data, suggesting that the ratio is at least only weakly dependent on frequency. In addition evidence is presented that the ratio is increasing with depth although attempts to extract specific gradients have failed because of the very poor distribution of S rays in the deepest mantle.
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Thompson, Delaine Rebecca. "Nonlinear waveform tomography : theory and application to crosshole seismic data". Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12666.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993.Includes bibliographical references (p. 175-183).
by Delaine Rebecca Thompson.
Ph.D.
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Kárason, Hrafnkell 1970. "Constraints on mantle convection from seismic tomography and flow modeling". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8059.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.Includes bibliographical references (p. 205-224).
In this thesis I combine high resolution seismic tomography and realistic flow modeling to constrain mantle convection. The bulk of the data used in the tomographic imaging are millions of P, pP and pwP travel time residuals, read from high frequency seismic records. The distribution of earthquakes and stations results in uneven data coverage and to improve the model I use core phases (PKP, Pdiff) for the deep mantle and surface reflected phases (PP) for the shallow mantle. Since narrow rays are not adequate for low frequency measurements, I construct broad 3-D sensitivity kernels to relate some of the added data to earth's structure. Furthermore, the parameterization of the tomographic model is adapted to data density and the model shows, among other details, the varying style of subduction in the shallow mantle and complex flow patterns around the transition zone between the upper and lower mantle. I develop a novel and efficient method of modeling buoyancy driven mantle flow in spherical geometry. Here, the linear Stokes equation is solved using a Green's function approach and 3-D surfaces, representing the boundaries of dense material, such as subducting slabs, are tracked through time.
by Hrafnkell Kárason.
(cont.) I describe the basis of the approach, represent tests, and investigate the thickening and slowing of subducting slabs for different viscosity contrasts between the upper and lower mantle. I compare seismic tomography, flow modeling and reconstructed plate motions associated with the collision of India to mainland Asia, in particular, the south and south-west motion of the Sunda block. This way I can evaluate subduction scenarios and make quantitative comparison between tomography and plate reconstructions. I conclude that a viscosity increase of -200 in the lower mantle, resulting in -10 times higher viscosity than previously estimated, best fits the observations. Juxtaposing the tomography, the flow models and inversion tests using the flow models as input, indicates that the results are robust.
Ph.D.
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Fang, Lihua. "Rayleigh wave tomography in North-China from ambient seismic noise". Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3623.
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2008/2009The theory and methodology of ambient noise tomography has been studied and applied to North-China successfully. Continuous vertical-component seismograms, spanning the period from January 1, 2007 to February 28, 2008 recorded by 190 broadband stations and 10 very broadband stations, have been used. The cross correlation technique has been applied to ambient noise data recorded by North-China Seismic Array for each station pairs of the array. Rayleigh wave group velocity dispersion curves are measured at periods between 4 s and 40 s by multiple filter technique. We obtain 5630 high quality dispersion curves. Surface wave tomography is conducted to generate group velocity maps with a grid spacing of 0.25º×0.25º. These maps display higher resolution and extend to shorter periods than previous surface wave tomography maps. Then genetic algorithm is used to invert pure path dispersion curves. The 3-D shear wave velocity structure from 0 to 50 km depth is readily constructed. To the authors' knowledge, the resolution presented here is, so far, the highest one in China mainland. The original results of this thesis are: 1, The SNR of Green Function is proportional to the square root of observation time and can be enhanced by using the symmetric component. The inhomogeneous distribution of seismic noise gives rise to the asymmetry of Green Function. Using more than one year's data, one can get more symmetric and higher SNR Green Function. 2, The characteristics of ambient seismic noise are different for different period bands. In 4-10 s, a coherent phase with large amplitude near zero lag time is observed. In 10-20 s, the sources of ambient seismic noise have a very clear seasonal variability. The azimuthal distributions of noise share a great similarity with the map of average ocean wave height map obtained by TOPEX-Poseidon. In 20-50s range, Rayleigh wave Green Functions are almost symmetrical and show less seasonal variation in both signal strength and directivity, which indicates that the distribution of noise is - ii - almost homogeneous. In 4-20s range, the amplitudes of positive and negative components of Green Functions are obviously asymmetrical, but the arrival times are almost identical, indicating that the distribution of noise has much influence on the amplitude of Green Function, but less influence on arrival time. 3, Tomographic maps at short periods reveal an evident lateral heterogeneity in the curst of North-China, quite well in agreement with known geological and tectonic features. The North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain basins show up as small low-velocity anomalies. 4, The 3-D S-wave crustal velocity model in North China shows a distinct low velocity belt with NW trend at 10 km of depth near Zhangjiakou-Bohai seismic zone. This low velocity belt and the southern margin of Yanshan high velocity anomaly draw the outline of Zhangjiakou-Bohai seismic zone and its northern border line. There is a well-defined low velocity zone in middle-to-lower crust (15-25 km) in the Beijing-Tianjin-Tangshan region, which may be caused by intrusion of hot mantle materials. 5, We analyzed the seismogenic structure near Tangshan，Luanxian and Ninghe earthquake region. We infer that these three earthquakes are mainly caused by vertical deformation of upper mantle and material exchange between crust and upper mantle. The magma intrudes the crust along faults near the boundary of crust and upper mantle, which leads to the low velocity anomaly in the uppermost mantle. The magma intrusion heats up the lower crustal material and drops its viscosity. Some minerals are dehydrated. The water moves up and is trapped in the middle crust. The existence of liquid affects the structure and composition of the fault zone, further changes the stress state, weakens the seismotectonic region and triggers the earthquakes.
XXI Ciclo
1981
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Pucciarelli, Giuseppe. "Seismic tomography of Italy (with special regard to Southern Tyrrhenian)". Doctoral thesis, Universita degli studi di Salerno, 2017. http://hdl.handle.net/10556/2569.
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2015 - 2016The topic of my PhD thesis is a seismic tomography which has as object of investigation Italy, particularly Southern Italy and Southern Tyrrhenian. This tomography has been obtained by means of inversion of teleseismic data. Seismic tomography is a method of investigation which is considerably stabilized in the field of Geophysics. Its goal is the achievement of a tridimensional velocity model of a subsoil of a determined area. For reaching this aim, it is necessary to gather arrival times of seismic events registered by seismic stations that are distributed in an opportune way on the area subject to process of investigation and an one-dimensional velocity model (that is, velocity only in function of depth). Through this last one, there is the computation of theoretical travel times for each pair seismic event – seismic station. This particular phase of method is called forward problem. Then, there is the computation of the difference between observed travel times and these theoretical travel times, a difference named residual. This is the description of so-called inverse problem. The computation happens in an iterative way and it stops when the residual is minimum. Obtained tridimensional velocity model corresponds with the model where residual is minimum. The entire process of operation of a seismic tomography is completely described in first chapter of this thesis. The second chapter describes the phenomen of subduction, that is of a particular process which happens, under determined conditions, at convergent boundaries of plates. I have dedicated a chapter to this phenomen because the area subject to this research, the basin of Southern Tyrrhenian, is a result of a roll-back subducting Ionian slab. After a paragraph dedicated to a general description of tectonic plates theory, other paragraphs describe the kinematics and the dynamics of subduction processes. This seismic tomography has been obtained by inversion of teleseismic travel times. This particular kind of choice has been made because teleseismic ray travel in upper mantle at high depths, so their inversion could supply us a good resolution of an area that we want to investigate until depth of 500-600 km. The third chapter of my PhD thesis is dedicated to teleseisms. In particular, there is a description of classification of seismic events according to their epicentral distance and how we can interpretate various seismic phases on a teleseismic seismogram. A paragraph is about the nomenclature of same seismic phases deriving from the reflection and the refraction of the waves on the discontinuity surfaces present in Earth's inner. The fourth and last chapter of my PhD thesis contains the results of research and their interpretation. First paragraph is dedicated to a brief summary of geological history of Southern Tyrrhenian. Second paragraph is dedicated to a description of software used for the research, that is FMTT (Fast Marching Teleseismic Transform), created by Nick Rawlinson in 2008. Third paragraph is dedicated to description of my data. I have utilised 1929 teleseisms (only P phases) recorded in period 1990-2012 by 122 southern Italian seismic station directly connected to ISC (International Seismological Centre). I have obtained several sections at various level of depth, from 25 km to 500 km and I have obtained several profiles NS and EW at fixed values of longitude from 14° to 16° and latitude, from 37° to 40° respectively. Results, compared with previous works in that area, confirm the presence of a subducting slab in Southern Tyrrhenian. Finally, my PhD thesis is enriched by various appendixes, which describe in a particular way mathematical techniques and geophysical definitions which I have used. [edited by author]
La mia tesi di Dottorato descrive una tomografia sismica dell'Italia, e in particolare di quella meridionale e del Basso Tirreno, ottenuta mediante l'inversione di dati telesismici. La tomografia sismica è oramai un metodo di indagine notevolmente consolidato nel campo della Geofisica e consiste nel ricavare un modello di velocità tridimensionale del sottosuolo di una determinata regione. Quest'ultimo si ottiene avendo a disposizione i tempi di arrivo di eventi sismici registrati da stazioni sismiche distribuite in maniera opportuna sull'area da indagare e un modello di velocità di partenza unidimensionale. Infatti, sfruttando quest'ultimo si calcolano per gli eventi sismici considerati dei tempi di arrivo teorici (questa fase prende il nome di PROBLEMA DIRETTO). Poi si calcola la differenza tra i tempi di arrivo realmente osservati e quelli teorici, che prende il nome di residuo (questa fase prende il nome di PROBLEMA INVERSO) e si procede in maniera iterativa in maniera che il residuo sia minimo. Il modello di velocità da ottenere è quello che corrisponde al residuo minimo. Il primo capitolo della tesi descrive la trattazione matematica della tomografia sismica, dopo un paragrafo introduttivo dedicato all'uso in generale dei metodi inversi in geofisica. La tomografia sismica si dice locale se gli eventi considerati sono locali. Si dice telesismica – come quella oggetto della mia tesi – se gli eventi considerati sono, lapalissianalmente, telesismi. Il secondo capitolo parla quindi dei telesismi, della loro definizione riguardo alla classificazione degli eventi sismici in base alla distanza epicentrale e delle fasi sismiche che si possono leggere da un sismogramma di un telesisma. Questo capitolo comprende un paragrafo sulla nomenclatura delle fasi sismiche e soprattutto quelle derivanti dalla riflessione e rifrazione delle onde su tutte le superfici di discontinuità presenti all'interno della Terra. E, a tal proposito, il terzo capitolo è un'introduzione alla struttura dell'interno della Terra con attenzione particolare che viene rivolta al fenomeno della subduzione. Questo perché uno slab di subduzione è presente all'interno del Basso Tirreno, zona “protagonista” della mia indagine tomografica. Il quarto capitolo è dedicato alla storia geologica del Basso Tirreno e alle evidenze delle precedenti indagini geofisiche che hanno visto questa area sotto la lente di ingrandimento. L'ultimo capitolo riguarda i risultati della mia indagine e la loro interpretazione. Ho utilizzato i tempi di arrivo di fasi P di 1929 telesismi (selezionati in base a un intervallo di magnitudo, a un minimo di stazioni registranti e all'intervallo di residuo di stazione) registrati nel periodo 1990-2012 da 122 stazioni dell'Italia centro-meridionale collegate all'ISC (International Seismological Centre). I risultati sembrerebbero, confrontati con quelli dei lavori precedenti, confermare la presenza di uno slab di subduzione nel Basso Tirreno. [a cura dell'autore]
XV n.s. (XXIX )
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Liu, Kui. "Surface Wave Propagation and Global Crustal Tomography". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/25428.
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In this thesis, a finite-frequency theory is developed to calculate Born sensitivity kernels for Rayleigh-wave phase and amplitude measurements that are valid in regions near seismic stations. Calculations of sensitivity kernels for inter-station measurements show that exact travelling-wave representation of Green tensor is necessary when station spacing is close to or smaller than the seismic wavelength. This finite-frequency theory will allow us to take advantage of dense seismic arrays to obtain high-resolution surface-wave tomography using inter-station measurements.
The non-linear dependence of surface wave phase upon large perturbations in crustal thickness as well as finite-frequency effects in global surface-wave tomography are investigated using wave propagation simulations. Calculations show that non-linearity as well as finite-frequency effects can be accounted for by using 2D phase-velocity kernels for boundary perturbations. A 3D-reference tomographic approach is developed for iterative inversions of global crustal structure where Frechet kernels are calculated in 3D reference models.
A global dataset of minor-arc and major-arc Rayleigh wave dispersion measurements at periods between 25 seconds and 100 seconds are built and global phase velocity maps based on the dataset are obtained using diffractional tomography. The phase velocity model confirms many general features associated with surface tectonics including the ocean-continent dichotomy and the signature of lithospheric cooling in oceanic plates. There are significant differences between the phase velocity model and calculations based on a current global model CRUST2.0+S20RTS in oceanic regions, Archean and Proterozoic cratons as well as orogenic belts. In addition, the high resolution phase velocity maps reveal a major change in the distribution of small scale anomalies in the Pacific at different wave periods.Ph. D.
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Adiya, Munkhsaikhan. "Seismic activity near Ulannbaatar : implication for seismic hazard assessment". Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH007/document.
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On observe depuis 2005 une sismicité intense à 10 km d'Oulan Bator ce qui a permis d'identifier une faille active, Emeelt, sur le terrain. Après le calcule d'un modèle de vitesse 3D, j'ai appliqué la tomographie double différence pour obtenir une localisation précise des séismes. Ils marquent au moins trois branches parallèles orientées N147° comme la faille vue en surface. L'activité sur la faille principale d'Emeelt (MEF) s’étend sur 15 km, les branches Ouest et Est, moins actives, sur 10 km. La profondeur de l'activité s'étend entre 4 et 15 km. L'activité sismique semble concentrée à l'intersection avec des failles Mésozoïques et les contrastes Vs/Vs suggèrent la présence de fluides. Les 10 essaims identifiés montrent une activité croissante et une migration spatiale avec le temps. Le calcul de 2 scénarios possibles, un M ~ 6.4 et un M ~ 7, indique un important impact sur la ville d'Oulan Bator, avec une intensité minimum de VIII et localement IX pour M=6.4 et X pour M=7We observe since 2005 a high seismic activity at 10 km from Ulaanbaatar that allowed us to identify a new active fault, Emeelt, in the field. After computing a 3D velocity model, I applied Double-Difference tomography to obtain a precise localization of earthquakes. They trace at least three parallel branches oriented N147° like the fault seen at surface. The seismic activity on the Main Emeelt Fault (MEF) is along at least 15 km, on the West and East branches, less active, along 10 km. The depth of the seismicity extends between 4 and 15 km. The activity seems concentrated at the intersection with Mesozoic faults and Vp/Vs contrast suggests the presence of fluids. The 10 swarms identified show an increasing activity and a spatial migration with time. The calculation of 2 possible scenarios, one M ~ 6.4 and one M ~ 7, shows an important impact on Ulaanbaatar, with a minimum intensity of VIII and IX for M=6.4 and X for M=7
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Johnson, Stuart G. "Applications of global seismic tomography and analysis of variational methods for the solution of the linearly attenuating frequency domain wave equation /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823696.
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Pyakurel, Sandeep. "3D P- and converted shear wave characteristics of the Morrow production trend in the Buffalo Valley field, Chaves-Eddy County, New Mexico". Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4256.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xi, 145 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 141-145).
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Frommel, Jamin C. "INTEGRATED GEOPHYSICAL INVESTIGATION OF KARST FEATURES – INNER BLUEGRASS REGION OF KENTUCKY". UKnowledge, 2012. http://uknowledge.uky.edu/ees_etds/5.
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High-resolution electrical-resistivity, seismic-refraction, and seismic-reflection surveys were performed at three locations in the Inner Bluegrass Region of Kentucky along coincident survey lines in order to correlate results and determine which method is most effective at locating karst features in this area. The first two survey locations at Slack’s Cave and the Kentucky Horse Park were chosen in order to investigate known karst features. High and low electrical-resistivity anomalies were correlated to air- and water-filled karst voids, respectively. Seismic velocity anomalies, including parabolic time suppressions, amplitude terminations, and surface-wave backscatters, were also observed and correlated to these karst voids. These findings were applied to a third location along Berea Road in order to investigate undiscovered karst voids. Three seismic targets were selected based on backscatter anomaly locations and were aligned in a northwest trend following the general bedrock dip, joint orientations, and suspected conduit orientation. Overall, the seismic-reflection method provided the highest resolution and least ambiguous results; however, integration of multiple methods was determined to help decrease ambiguities in interpretation created by the inherent non-uniqueness found in the results of each method.
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Baumann-Wilke, Maria. "Combining body wave tomography, surface wave inversion, seismic interferometry and laboratory measurements to characterize the black shales on Bornholm at different scales". Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2013/6900/.
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Black shales are sedimentary rocks with a high content of organic carbon, which leads to a dark grayish to black color. Due to their potential to contain oil or gas, black shales are of great interest for the support of the worldwide energy supply. An integrated seismic investigation of the Lower Palaeozoic black shales was carried out at the Danish island Bornholm to locate the shallow-lying Alum Shale layer and its surrounding formations and to characterize its potential as a source rock. Therefore, two seismic experiments at a total of three crossing profiles were carried out in October 2010 and in June 2012 in the southern part of the island. Two different active measurements were conducted with either a weight drop source or a minivibrator. Additionally, the ambient noise field was recorded at the study location over a time interval of about one day, and also a laboratory analysis of borehole samples was carried out. The seismic profiles were positioned as close as possible to two scientific boreholes which were used for comparative purposes.
The seismic field data was analyzed with traveltime tomography, surface wave inversion and seismic interferometry to obtain the P-wave and S-wave velocity models of the subsurface. The P-wave velocity models which were determined for all three profiles clearly locate the Alum Shale layer between the Komstad Limestone layer on top and the Læså Sandstone Formation at the base of the models. The black shale layer has P-wave velocities around 3 km/s which are lower compared to the adjacent formations. Due to a very good agreement of the sonic log and the vertical velocity profiles of the two seismic lines, which are directly crossing the borehole where the sonic log was conducted, the reliability of the traveltime tomography is proven. A correlation of the seismic velocities with the content of organic carbon is an important task for the characterization of the reservoir properties of a black shale formation. It is not possible without calibration but in combination with a full 2D tomographic image of
the subsurface it gives the subsurface distribution of the organic material.
The S-wave model obtained with surface wave inversion of the vibroseis data of one of the profiles images the Alum Shale layer also very well with S-wave velocities around 2 km/s. Although individual 1D velocity models for each of the source positions were determined, the subsurface S-wave velocity distribution is very uniform with a good match between the single models. A really new approach described here is the application of seismic interferometry to a really small study area and a quite short time interval. Also new is the selective procedure of only using time windows with the best crosscorrelation signals to achieve the final interferograms. Due to the small scale of the interferometry even P-wave signals can be observed in the final crosscorrelations.
In the laboratory measurements the seismic body waves were recorded for different pressure and temperature stages. Therefore, samples of different depths of the Alum Shale were available from one of the scientific boreholes at the study location. The measured velocities have a high variance with changing pressure or temperature. Recordings with wave propagation both parallel and perpendicular to the bedding of the samples reveal a great amount of anisotropy for the P-wave velocity, whereas the S-wave velocity is almost independent of the wave direction. The calculated velocity ratio is also highly anisotropic with very low values for the perpendicular samples and very high values for the parallel ones. Interestingly, the laboratory velocities of the perpendicular samples are comparable to the velocities of the field experiments indicating that the field measurements are sensitive to wave propagation in vertical direction.
The velocity ratio is also calculated with the P-wave and S-wave velocity models of the field experiments. Again, the Alum Shale can be clearly separated from the adjacent formations because it shows overall very low vP/vS ratios around 1.4. The very low velocity ratio indicates the content of gas in the black shale formation. With the combination of all the different methods described here, a comprehensive interpretation of the seismic response of the black shale layer can be made and the hydrocarbon source rock potential can be estimated.Schwarzschiefer sind Sedimentgesteine, die einen hohen Gehalt an organischem Kohlenstoff aufweisen, was zu einer dunkelgrauen bis schwarzen Färbung führt. Da Schwarzschiefer das Potenzial besitzen, Öl oder Gas zu enthalten und somit zur weltweiten Energieversorgung beitragen könnten, sind sie von großem Interesse. Mit Hilfe der Kombination verschiedener seismischer Messverfahren wurden die Schwarzschiefer des Unteren Paläozoikums auf der dänischen Insel Bornholm untersucht um den oberflächennahen Alaunschiefer und dessen Umgebungsgestein dort zu lokalisieren und sein Potenzial als Muttergestein abzuschätzen. Dafür wurden im Oktober 2010 und im Juni 2012 im südlichen Teil der Insel zwei seismische Experimente auf insgesamt drei sich kreuzenden Profilen durchgeführt. Für zwei aktive seismische Messungen wurden ein Fallgewicht und ein Minivibrator als Quellen genutzt. Zusätzlich wurde im Messgebiet noch das Wellenfeld des umgebenden Rauschens über einen Zeitraum von etwa einem Tag aufgezeichnet. Außerdem wurden Labormessungen an Bohrkernen aus dem Alaunschiefer durchgeführt. Die seismischen Messprofile befanden sich so nah wie möglich an zwei wissenschaftlichen Bohrungen, die für Vergleichszwecke genutzt wurden. Um die P- und S-Wellengeschwindigkeitsmodelle des Untergrundes zu erhalten wurden die seismischen Felddaten mittels Laufzeittomographie, Oberflächenwelleninversion und seismischer Interferometrie ausgewertet. Die P-Wellenmodelle, die für alle drei seismischen Profile erstellt wurden, zeigen den Alaunschiefer zwischen dem Komstad Kalkstein, der den Alaunschiefer überdeckt, und der Læså Sandsteinformation, die die Basis der Modelle bildet. Für die Schwarzschieferschicht ergeben sich mit rund 3 km/s deutlich geringere P-Wellengeschwindigkeiten als für die umgebenden Gesteine. Zwei seismische Profile liegen direkt an einer der Bohrungen, für die verschiedene Bohrloch-Logs durchgeführt wurden. Der Vergleich des Sonic-Logs mit den vertikalen Geschwindigkeitsprofilen beider Modelle am Bohrpunkt zeigt eine sehr gute übereinstimmung aller Geschwindigkeiten. Dies ist ein Indiz für die Plausibilität der durchgeführten Laufzeittomographie. Um die Reservoireigenschaften der Schwarzschieferschicht einordnen zu können, wurde versucht, die seismischen Geschwindigkeiten mit dem Gehalt an organischem Material zu korrelieren. Ohne geeignete Kalibrierung ist diese Korrelation schwierig, kann aber mit Hilfe der Tomographieergebnisse ein zweidimensionales Abbild der Verteilung des organischen Materials im Untergrund liefern. Auch das S-Wellengeschwindigkeitsmodell, welches mit der Oberflächenwelleninversion der Vibroseisdaten erstellt wurde, bildet den Alaunschiefer gut ab. Hierbei zeigen sich S-Wellengeschwindigkeiten um 2 km/s. Obwohl jeweils nur 1D-Modelle für jede Quellposition bestimmt wurden, ergibt sich für die gesamte Untergrundstruktur des untersuchten Profils ein einheitliches Bild der Geschwindigkeiten. Einen sehr neuen Ansatz bildet die Anwendung der seismischen Interferometrie auf ein sehr kleines Untersuchungsgebiet und über einen sehr kurzen Zeitraum. Neu ist außerdem, dass für die Bestimmung der endgültigen Interferogramme nur Zeitfenster der Kreuzkorrelationen ausgewählt werden, in denen die Signalqualität hinreichend gut ist. In den berechneten Kreuzkorrelationen sind sogar P-Wellen enthalten, was auf die geringen Abstände der seismischen Rekorder zurück zu führen ist. Bei den Labormessungen wurden die Raumwellen für verschiedene Drücke und Temperaturen aufgezeichnet. Die Messungen der Geschwindigkeiten sowohl parallel als auch senkrecht zur Schichtung der Proben zeigen eine starke Anisotropie für die P-Welle. Dagegen scheint die S-Wellengeschwindigkeit fast unabhängig von der Ausbreitungsrichtung der Wellen zu sein. Auch das Verhältnis der Geschwindigkeiten weist starke Anisotropie auf. Für die Wellenausbreitung senkrecht zur Schichtung zeigen sich sehr niedrige Werte, die Werte für die Messungen parallel zur Schichtung sind dagegen deutlich erhöht. Ein interessanter Aspekt der aus den Labormessungen resultiert ist, dass die Geschwindigkeit der Messungen senkrecht zur Schichtung mit den Geschwindigkeitswerten der Feldmessungen übereinstimmen. Damit scheinen die Feldmessungen besonders die Ausbreitung der Wellen in vertikaler Richtung zu registrieren. Das Geschwindigkeitsverhältnis wurde auch mit den P- und S-Wellenmodellen der Feldexperimente berechnet. Auch hier hebt sich der Alaunschiefer mit deutlich verringerten Werten um 1.4 vom Umgebungsgestein ab. Solch geringe Werte für das Verhältnis der Geschwindigkeiten deutet auf den Gehalt von Gas im Schwarzschiefer. Mit der Kombination der verschiedenen Methoden ist es möglich, die seismische Antwort der Schwarzschieferschicht umfassend zu beschreiben und Schlussfolgerungen darüber zu ziehen, ob die hier untersuchte Schwarzschieferschicht das Potenzial hat als Kohlenwasserstofflagerstätte zu fungieren.
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Viso, Richard F. "Sequential development of the Gassaway structure in Braxton County, West Virginia". Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=681.
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Thesis (M.S.)--West Virginia University, 1999.Title from document title page. Document formatted into pages; contains x, 106 p. : ill. (some col.), maps Includes abstract. Includes bibliographical references (p. 100-102).
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Hammond, William Charles. "Dynamics, flow and melt content of the Southern East Pacific Rise upper mantle from teleseismic tomography /". view abstract or download file of text, 2000. http://wwwlib.umi.com/cr/uoregon/fullcit?p9998033.
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Thesis (Ph. D.)--University of Oregon, 2000.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 139-151). Also available for download via the World Wide Web; free to University of Oregon users.
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Kelly, Irene G. "Modeling and migration of Hibernia seismic data". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0010/MQ34191.pdf.
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Boyce, Alistair. "The Proterozoic building of North America : insights from broadband seismic tomography". Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/62331.
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Cratons, the Archean (≥ 2.5 Ga) cores of the continents are the longest-lived features of Earth’s surface. They are underlain by cold, iron-depleted, thick (>250 km), seismically fast lithospheric mantle roots or keels that have survived thermal and chemical erosion over multiple Wilson cycles. Recently however, numerous studies have shown that cratonic mantle lithosphere can undergo modification andmay be removed entirely. I use passive-source seismology to investigate this further for the Superior Craton of North America and its abutting Proterozoic platform. Initially, I use P- and S-wave relative arrival-time tomography to investigate the regional seismic structure of southeast Canada. Here, three broad zones of decreasing seismic wavespeed span the Archean Superior, Proterozoic Grenville and Phanerozoic Appalachian provinces, respectively. A vertical boundary in wavespeed beneath the Grenville Front is interpreted as evidence for subduction-driven metasomatic enrichment of the Laurentian margin. Due to the loss of the background mean velocity structure, relative arrival-time datasets are not easily combined and are also unsuitable for estimation of the physical properties of the mantle. To address this, I develop the Absolute Arrival-time Recovery Method (AARM) to retrieve absolute arrival-times from temporary seismograph networks, whose data are often noisy. Tests indicate that AARM picks are accurate to ≤0.25 s, akin to uncertainties in ISC bulletins. As a result, small aperture, temporary deployments now represent an exploitable resource with which to fill gaps in global seismic tomographic studies. Finally, I incorporate multiple regional networks from eastern Canada into a continental P-wave absolute arrival-time tomographic inversion to produce the most up-to-date compressional wavespeed image of the North American lithosphere. These results show along-strike variability in upper lithospheric velocity structure within the Proterozoic Grenville Orogen (1.3 − 1.0 Ga). When reconciled with the geological record, these results may provide the first seismological evidence for delamination of subcontinental lithospheric mantle in a Proterozoic large, hot, orogen.
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Ma, Xu. "Passive Seismic Tomography and Seismicity Hazard Analysis in Deep Underground Mines". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51266.
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Seismic tomography is a promising tool to help understand and evaluate the stability of a rock mass in mining excavations. Lab measurements give evidence that velocities of seismic wave propagations increase in high stress areas of rock samples. It is well known that closing effects of cracks under compressive pressures tend to increase the effective elastic moduli of rocks. Tomography can map stress transfer and redistribution and further forecast rock burst potential and other seismic hazards, which are influenced by mining. Recorded by seismic networks in multiple underground mines, arrival time of seismic waves and locations of seismic events are used as sources of tomographic imaging survey. An initial velocity model is established according to properties of a rock mass, then velocity structure is reconstructed by velocity inversion to reflect the anomalies of the rock mass. Mining-induced seismicity and double-difference tomographic images of rock mass in mining areas are coupled to show how stress changes with microseismic activities. Especially, comparisons between velocity structures of different periods (before and after rock burst) are performed to analyze effects of rock burst on stress distribution. Tomographic results show that high velocity anomalies form in the vicinity of rock burst before the occurrence, and velocity subsequently experiences a significant drop after the occurrence of rock burst. In addition, regression analysis of travel time and distance indicates that the average velocity of all the monitored region appears to increase before rock burst and reduce after them. A reasonable explanation is that rock bursts tend to be triggered in highly stressed rock masses. After the energy release of rock bursts, stress relief is expected to exhibit within rock mass. Average velocity significantly decreases because of lower stresses and as a result of fractures in the rock mass that are generated by shaking-induced damage from nearby rock burst zones. Mining-induced microseismic rate is positively correlated with stress level. The fact that highly concentrated seismicity is more likely to be located in margins between high-velocity and low-velocity regions manifests that high seismic rates appear to be along with high stress in rock masses. Statistical analyses were performed on the aftershock sequence in order to generate an aftershock decay model to detect potential hazards and evaluate stability of aftershock activities.Ph. D.