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With the rapid growth of seismic data volumes, traditional automated processing methods, which have been in use for decades, face increasing challenges in handling these data, especially in noisy environments. Deep learning (DL) methods, due to their ability to handle large datasets and perform well in complex scenarios, offer promising solutions to these challenges. When I started my Ph.D. degree, although a sizeable number of researchers were beginning to explore the application of deep learning in seismology, almost no one was involved in the development of much-needed automated data annotation tools and deep learning training platforms for this field. In other rapidly evolving fields of artificial intelligence, such automated tools and platforms are often a prerequisite and critical to advancing the development of deep learning. Motivated by this gap, my Ph.D. research focuses on creating these essential tools and conducting critical investigations in the field of earthquake detection and phase picking using DL methods. The first research chapter introduces QuakeLabeler, an open-source Python toolbox that facilitates the efficient creation and management of seismic training datasets. This tool aims to address the laborious process of producing training labels in the vast amount of seismic data available today. Building on this foundational tool, the second research chapter presents Blockly Earthquake Transformer (BET), a deep learning platform that provides an interactive dashboard for efficient customization of deep learning phase pickers. BET aims to optimize the performance of seismic event detection and phase picking by allowing easy customization of model parameters and providing extensions for transfer learning and fine-tuning. The third and final research chapter investigates the performance of DL pickers by examining the effect of training data size and deployment settings on phase picking accuracy. This investigation provides insight into the optimal size of training datasets, the suitability of DL pickers for new target regions, and the impact of various factors on training and on model performance. Through the development of these tools and investigations, this thesis contributes to the application of DL in seismology, paving the way for more efficient seismic data processing, customizable model creation, and a better understanding of DL model performance in earthquake detection and phase-picking tasks.

An approach to balance the amplitude of seismic data in the Ï -Ï domain is introduced in this study. The idea of amplitude balancing technique is based on the following observation: In the Ï -Ï domain, direct wave, ground-roll, primary reflection, multiple and refraction arrivals are located at different regions. These regions can be viewed as signal region and noise region. By increasing the amplitudes in the signal region and suppressing the amplitudes in the noise region, so called amplitude balancing in T-Ï domain, the signal-to-noise ratio of seismic data can be improved. The Ï -Ï domain amplitude balancing scheme is tested and calibrated on synthetic seismic data using AIMS®' package. The modeled data is also used to illustrate transformation (slant stacking) to and from Ï -Ï domain. The signal-to-noise ratio enhancement using amplitude balancing in Ï -Ï domain is illustrated. This general discussion also includes aliasing effect of slant stack and deconvolution in Ï -Ï domain. After the calibration with syn1hetic data, the amplitude balancing in Ï -Ï domain is applied to real seismic data recorded on the Atlantic Coastal Plain near Richmond, Virginia and Aiken, South Carolina to explore the possibilities of enhancing the quality of seismic data. Processing of synthetic and real data is carried out on VAX 11/785 and Sun Sparc 10 workstation at the Regional Geophysics Laboratory at Virginia Polytechnic Institute and State University using DISCO@2 seismic data processing package. The results suggest that Ï -Ï domain amplitude balancing can be combined into conventional seismic data processing sequence to improve the signal-to-noise ratio and thus give a better imaged seismic section. Extensive tests carried out indicate that choice of ray parameter range, the degree of amplitude change, are important aspects of the processing in Ï -Ï domain. In this study, a complete data processing was carried out to generate a stack section of NRC line 2 in Virginia while the amplitude balancing in Ï -Ï domain was incorporated into a conventional processing scheme. The Ï -Ï domain processing of NRC line 2 improved the data quality. The signal-to-noise ratio enhancement obtained by the amplitude balancing in Ï -Ï domain led to test the method to improve weak reflections from within the Dunbarton Triassic basin on SRP line 2EXP in South Carolina. After the application of amplitude balancing in Ï -Ï domain, CMP gathers showed enhanced signal-to-noise ratio, although the improvement became almost indiscernible after stack. / Master of Science

The Centroid-Moment Tensor (CMT) method allows an optimal point-source description of an earthquake to be recovered from a set of seismic observations, and, for over 30 years, has been routinely applied to determine the location and source mechanism of teleseismically recorded earthquakes. The CMT approach is, however, entirely general: any measurements of seismic displacement fields could, in theory, be used within the CMT inversion formulation, so long as the treatment of the earthquake as a point source is valid for that data. We modify the CMT algorithm to enable a variety of near-field seismic observables to be inverted for the source parameters of an earthquake. The first two data types that we implement are provided by Global Positioning System receivers operating at sampling frequencies of 1,Hz and above. When deployed in the seismic near field, these instruments may be used as long-period-strong-motion seismometers, recording displacement time series that include the static offset. We show that both the displacement waveforms, and static displacements alone, can be used to obtain CMT solutions for moderate-magnitude earthquakes, and that performing analyses using these data may be useful for earthquake early warning. We also investigate using waveform recordings - made by conventional seismometers deployed at the surface, or by geophone arrays placed in boreholes - to determine CMT solutions, and their uncertainties, for microearthquakes induced by hydraulic fracturing. A similar waveform inversion approach could be applied in many other settings where induced seismicity and microseismicity occurs.

Crosshole seismic techniques can be used to gain a large amount of information about the properties of the rock mass between two or more boreholes. The bulk of this thesis is concerned with two crosshole seismic processing techniques and their application to real data. The first part of this thesis describes the application of traveltime and amplitude tomographic processing in the monitoring of a simulated EOR project. Two physical models were made, designed to simulate 'pre-flood' and 'post-flood' stages in an EOR project. The results of the tomography work indicate that it is beneficial to perform amplitude tomographic processing of cross-well data, as a complement to traveltime inversion, because of the different response of velocity and absorption to changes in liquid/gas saturations for real reservoir rocks. The velocity tomograms image the flood zone quite accurately. Amplitude tomography shows the flood zone as an area of higher absorption but does not image its boundaries as precisely, because multi-pathing and diffraction effects are not accounted for by the ray-based techniques used. Part two is concerned with the crosshole seismic reflection technique, using data acquired from a site in northern England. The processing of these data is complex and includes deconvolution, wavefield separation and migration to a depth section. The two surveys fail to pin-point accurately the position of a large fault; the disappointing results, compared to earlier work in Yorkshire, are attributed to poorer generation of compressional body waves in harder Coal Measures strata. The final part of this thesis describes the results from a pilot seismic reflection test over the Tertiary igneous centre on the Isle of Skye, Scotland. The results indicate that the base of a large granite body consists of interlayered granites and basic rocks between 2.1 and 2.4km below mean sea level.

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Two new analysis methods for solar seismology are developed. Called the continuous orthonormalization (CON) and adjoint methods, their use enables both solar eigenfrequencies and eigenfrequency sensitivities (partial derivatives with respect to solar model parameters) to be computed more accurately and efficiently than with existing methods. The CON method integrates an eighth-order nonlinear system of ordinary differential equations (ODEs) which defines the linear adiabatic nonradial oscillation modes of the Sun. (The Cowling approximation is not used.) All normal modes of oscillation are treated identically, regardless of their type (pressure, gravity or fundamental) or their predominant location inside the Sun. The adjoint method integrates a related eighth-order linear inhomogeneous system of ODEs. From the resultant solution, an eigenfrequency's partial derivatives with respect to an extensive set of solar model parameters may be computed simultaneously. Extensive numerical tests confirm the validity of the two new methods. Eigenfrequencies obtained via the CON method have seven significant digits and match within 1% the eigenfrequencies obtained via finite difference or mesh approaches. (Exact agreement is neither expected nor attainable because differently defined solar models are analyzed. The CON method analyzes models which are functionally specified on a continuum of radial points; the other methods analyze models defined on discrete sets of radial points.) Eigenfrequency sensitivities obtained via the adjoint method match within 2% the results obtained by explicitly perturbing the solar model parameters and recomputing the eigenfrequencies. The usefulness and power of the two new methods are demonstrated by applying them to the solution of an elementary solar inversion problem. A sample solar model's f-mode frequencies (obtained via the CON method) are iteratively driven into agreement with an observed set of f-mode frequencies. Adjoint sensitivity results are used to alter solar model parameters within hundreds of radial bins. The frequency movement is large, comparable to the frequency separation between adjacent degree f-modes. Model changes are also large; the density near the base of the convection zone is roughly doubled, while slightly further out it is halved.

The purpose of the thesis is the determination of potentially seismic active sources and of the dynamic response evaluation of surface and subsurface structure at sites where the geometric and dynamic properties of the ground can strongly amplify seismic motions. A combination of methods involving the study of geology, geophysics and seismology disciplines permitting cross-comparison of techniques in a robust approach is applied to address these issues. The study area is focused in Kastelli-Kissamou and Paleohora half graben basins in northwestern and southwestern Crete that is located in one of the most seismically active parts of the Africa-Eurasia collision zone. Ground truthed geological field survey, 2D Electrical Resistivity Tomography (ERT), Horizontal to Vertical Spectra Ratio (HVSR) technique using microtremors and microseismicity study are conducted. Microseismicity study involves two different earthquake dataset acquired from a regional permanent network installed on Crete and local temporal network installed on Paleohora. 2D Electrical resistivity tomography (ERT) reveals seven faults in the territory of Kastelli-Kissamou and three faults large scale faults in the territory of Paleohora basin. HVSR technique using microtremors is applied only in the populated area of Kastelli and Paleohora basins and reveals five fault zones in Kastelli and four major fault zones in Paleohora crosscutting the densely populated areas. The effects of the surface and subsurface structure are well patterned in the horizontal to vertical spectra ratios. One amplified clear frequency, two high amplified clear frequencies, broad and flat or low amplitude HVSR peaks attributes the effects of surface and subsurface structure on seismic ground motion. The effects of soft rocks, stiff soils, thick and thin alluvial deposits, fault zones, lateral heterogeneities and discontinuities on seismic ground motion are determined. The higher ground amplification level is observed in Paleohora (A=5.7) compared to Kastelli (A=3.4). Three case studies of building vulnerability evaluation in Paleohora half-graben basin using HVSR technique and microtremors are presented. Temporal seismological network is installed in the territory of Paleohora to study the seismotectonic setting of southwestern Crete. Microseismicity using data from the permanent seismological regional network of Crete is used to compare the seismicity of the study areas.

In general, the depths of shallow earthquakes are poorly resolved in current catalogues. Variations in depth of ±10 km can significantly alter the tectonic interpretation of such earthquakes. If the depth of a seismic event is in error then moment tensor estimates can also be significantly altered. In the context of nuclear-test-ban monitoring, a seismic event whose depth can be confidently shown to exceed say, 10km, is unlikely to be an explosion. Surface wave excitation is sensitive to source depth, especially at intermediate and short periods, owing to the approximate exponential decay of surface wave displacements with depth. The radiation pattern and amplitude of surface waves are controlled by the depth variations in the six components of the strain tensor associated with the surface wave eigenfunctions. The potential exists, therefore, for improvements to be made to depth and moment tensor estimates by analysing surface wave amplitudes and radiation patterns. A new method is developed to better constrain seismic source parameters by analysing 100-20s period amplitude spectra of fundamental-mode surface waves. Synthetic amplitude spectra are generated for all double-couple sources over a suitable depth range and compared with data in a grid-search algorithm. Best fitting source parameters are calculated and appropriate bounds are placed on these results. This approach is tested and validated using a representative set of globally-distributed events. Source parameters are determined for 14 moderately-sized earthquakes (5.4 ≤ M_w ≤ 6.5), occurring in a variety of tectonic regimes with depths calculated between 4-39km. For very shallow earthquakes the use of surface wave recordings as short as 15s is shown to improve estimates of source parameters, especially depth. Analysis of aftershocks (4.8 ≤ M_w ≤ 6.0) of the 2004 great Sumatra earthquake is performed to study the depth distribution of seismicity in the region. Three distinct tectonic regimes are identified and depth estimates calculated between 3-61km, including the identification of one CMT depth estimate to be in error by some 27km.