In this research, a new measuring method to detect shear parameters in fluid mud is proposed, namely using shear waves, or S-waves opposed to the conventional pressure waves, or P-waves. Currently, detecting fluid mud is done by the use of P-waves. This paper shows that conventional P-waves velocity measurements are unsuitable for linking velocities to the yield stress, which is likely caused due to gas in the mud. Opposed to this, S-wave velocities do show an logarithmic increase, which most likely can be linked to the yield stress development of fluid mud. Both S-wave velocities and yield-point measurements show an exponential increase over time and, because of this, it could be that there is a linear relation between them. The difference why S-waves are more suitable for shear-strength measuring is due to their nature of propagation. S-waves do not propagate through gas and are therefore hardly effected by gas production, opposed to P-waves. For this research, both P-and S-wave velocities are estimated from a transmission seismic experiment. Also, a frequency analysis has been conducted showing large similarities over time and for dissimilarities between different mud samples. The yield-point measurements are derived from a rheometer with the same mud sample used for the seismic experiments. Besides a velocity analysis from the transmission measurements, also a reflection measurement has been conducted. The aim for this is to detect converted P-to S-waves and to detect the Scholte wave. Furthermore, a dispersion analysis has been conducted, which is likely important since the relative change in S-wave velocities is small and the velocities are frequency-dependent.

Considering the inherent uncertainty of structural geological models, the non-uniqueness of geophysical inverse problems, and the growing availability of data, there is a need for methods that combine different types of data and allow for updating knowledge in a consistent way. By making use of the development of efficient, gradient-based MCMC algorithms, probabilistic inversion provides a tool for this. To test to what extent we can reduce the uncertainty of an initial geological model, we integrate geological modelling into a Bayesian inverse framework. Additional information can then be included in this inverse framework through likelihood functions. The proposed methodology is tested on a geological model of the structurally complex Kevitsa deposit in Finnish Lapland. By starting with an initial interpretation-based 3D geological model, we define the uncertainties in our geological model by means of probability density functions. Magnetic data and geological interpretations of borehole data are used to define geophysical and geological likelihoods respectively. To use the magnetic data in the inference, the mathematical description of the magnetic forward calculation is implemented for a 3D voxelised space, linking the geophysical data through magnetic rock properties to the uncertain structural parameters. The result of the inverse problem is presented in the form of probability distributions and ensembles of the realised models through visual analysis. The former is a statistical consideration of the results, whereas the latter is a visual representation for direct interpretation in a geological sense. The uncertainties in these visual representations are best presented by means of information entropy, which allows for a quantitative analysis. The results show that well-defined likelihood functions can reduce uncertainties in geological models and build on the complementary strength of different types of data. Where probabilistic inversion inherently provides uncertainty analysis, finding a single representative solution is less trivial. Therefore we conclude that the strength of the used methodology mainly lies in data integration and uncertainty quantification.

The recent discovery of the Zama field in offshore Sureste Basin in the southern Gulf of Mexico has piqued interest in the Mexican petroleum industry regarding the hydrocarbon potential within the region. In this study, a deposition-only thermal model was developed in an area of interest (AOI) in this region. Using structural input obtained from seismic interpretation conducted in Petrel©, the model was constructed and simulated in PetroMod© to acquire initial estimates of the maturity of the Tithonian J100 source rock in the AOI in terms of the maturity parameters Vitrinite Reflectance (%Ro) and Transformation Ratio (TR). A one-at-a-time (OAT) sensitivity analysis approach was also undertaken to assess the impact of uncertainties in some inputs in isolation on the output maturity in order to identify key uncertain input parameters. Based on the modeling results, at the C-1 well location of interest within the AOI, the source rock was simulated to be within the wet gas generation window based on simulated %Ro values in the present, having emerged into oil window between 41 - 27 Ma (late Eocene-Oligocene) and into the wet gas window between 6 - 0.5Ma (late Miocene-Pleistocene). Across the wider AOI, present-day %Ro values indicate the predominant presence of late oil to wet gas generation windows, with most of the source rock across the AOI having emerged into the oil generation window between 23 Ma and 11.6 Ma (early to middle Miocene). The highest uncertainties in simulated %Ro values were associated with uncertainties in the Bajocian (J60) autochtonous salt sequence thickness distribution and with the maturity models used for model simulation. At the C-1 well location, TR values of 95% to near 100% in the present indicate that most of the kerogen (source rock organic matter) has already been converted into hydrocarbons, with kerogen conversion initiated between 55 - 48 Ma at the location. Across the wider AOI, average present-day TR values in the range of 81 - 97% were simulated. The highest uncertainties in simulated TR values were also associated with uncertainties in the Bajocian (J60) autochtonous salt sequence thickness distribution, and with the source rock maturation kinetics input used for model simulation. The timing of maturation of the J100 source rock at the C-1 well location - assumed to have been constrained by the OAT sensitivity analyses results for simplicity - in relation to the timing of other petroleum system elements and processes indicated by literature, suggests that hydrocarbon accumulations charged from the Tithonian source rock in the reservoir intervals in the well vicinity are possible i.e. presence of hydrocarbon accumulations cannot be ruled out based only on maturation timing considerations.

The Dutch infrastructure counts many bridges, the majority of which are built in concrete. These bridges have been designed and constructed according to safety codes. A lot of these bridges date from the previous century and have been designed conform outdated safety codes. Therefore, the main problem of these bridges is the uncertainty with regard to their structural health as well as their performance under the current loading conditions. The application of ‘smart aggregates’ could potentially solve these issues. Smart aggregates refer to a network of sensors that emit and receive wave signals inside the concrete structure. These sensor are embedded within the concrete and can be implemented in both new and existing structures. The changes in the medium with regard to the stresses are reflected by the phase changes of the wave signal measured by the smart aggregates. This information allows for the monitoring of the conditions of the bridge during its lifespan. The magnitude of the stress in certain parts of the structure could then indicate the need for maintenance at an early stage, thus preventing unnecessary maintenance while preserving the safety of the bridge. This method, however, requires a thorough understanding of the wave propagation inside a concrete medium subjected to a stress state. This thesis investigates how the relative wave-velocity change of a concrete-like medium is influenced by the stresses to which it is subjected. Throughout the report this relation is referred to as the acoustoelastic effect. The first part of the thesis is centered around the theoretical formulation of the acoustoelastic effect. During this study, the models of Murnaghan and Biot have been studied. Subsequently, their differences with respect to the fundamental assumptions have been indicated. Here, it has been found that the main difference between the two models is demonstrated by the way they regard the second-order deformation terms. Murnaghan assumed that these terms are significant and has included them in the constitutive relation. From the latter, Hughes and Kelly have derived expression for wave velocities of a stressed medium, which have been verified with experimental results. On the other hand, Biot adopted the theory of infinitesimal deformations which omits the second-order deformation terms. In addition he based his theory around the wave propagation of a bending rod and extended this model to a three-dimensional medium subjected to initial stresses. This generalisation of an approximated model has led to analytical expressions for the wave velocity of a stressed solid which are contradicted by experiments. From this comparison, it has been concluded that Murnaghan’s model results in the most accurate representation of the acoustoelastic effect. The second part of the thesis focuses on the verification of the theoretical acoustoelastic effect through experimental research. For the purpose of verifying the acoustoelastic effect as well as determining the third-order elastic coefficients of a concrete-like medium, four specimens have been tested. In order to investigate the influence of the inhomogeneity of the material on the changes in the wave velocity, two different material compositions have been investigated. The first type consists of a homogeneous cement paste, whereas the second type represents heterogeneous concrete including aggregates. During the experiment, the different waveforms have been repeatedly emitted through a specimen subjected to an uniaxial compression. The relative wave-velocity change has then been obtained by post-processing the acquired data, which has been compared with Murnaghan’s model. The conclusion of this research is that Murnaghan’s theory can be used to accurately predict the relative wave-velocity changes of the cement-paste specimens, and in particular the relative P-wave velocity changes. The results have shown that the radial recordings yield inconsistencies which can be attributed to the small dimensions of the specimens. Furthermore, the influence of the inhomogeneity of the material on the relative wave-velocity changes manifests itself through a discrepancy in the acoustoelasticity. Here, it is found that the ratio between the aggregate size, the specimen dimensions and the wavelength of the signal determines the sensitivity to the acoustoelastic effect. Therefore, before the data from the smart aggregates embedded in a real structure can be interpreted, the experiments need to be improved and expanded. It is important to investigate the acoustoelasticity of waves with non-orthogonal propagation and particle-oscillation direction, while applying various stress states to the medium. This is because the smart aggregates are arranged in a network, where the signals are emitted signals are propagating through the structure via arbitrary paths between various transducers.

We use ground and space geodetic data to study surface deformation and gravity change at Kīlauea volcano from January to September 2015. This period includes an episode of heightened activity in May 2015, which we refer to as ’the May 2015 event’. The data set consists of Global Navigation Satellite System (GNSS), tilt, visual and seismic time series along with 25 descending and 15 ascending acquisitions of the Sentinel-1a satellite in Interferometric Wide swath mode and microgravity surveys taken a few years before and just after the May 2015 event. We identify four different stages of surface deformation and volcanic activity during the May 2015 event which we attribute to the movement of magma and pressure changes in response to a magma supply and withdrawal imbalance in the shallow plumbing system. In particular, we model the deformation sources attributed to the Halema’uma’u reservoir (HMMR) and South caldera reservoir (SCR). The SCR was best described by inflation of a spheroidal at 2.8 (2.65-3.07) km depth below the Southern caldera region. The HMMR source was modelled by a point source deflation located East of the Halema’uma’u crater at 1.5 (0.95- 2.62) km depth. The surface microgravity changes which would result from changes in these reservoirs are significantly lower than the actually observed microgravity changes. We attribute this to the lack of complexity of the single point source model used. Mechanisms that add/remove mass from the subsurface without accompanying surface deformation, which are not part of the point source model, played a significant role. More frequent microgravity campaign surveys, if needed with a smaller network, are the only way to improve our understanding of these processes and help to quantify them.

The theory of seismic interferometry predicts that the cross-correlation (and possibly summation) between seismic recordings at two separate receivers allows the retrieval of an estimate of the inter-receiver response, or Green's function, from a virtual source at one of the receiver positions. Ideally, the recordings must consist of the responses from a homogeneous distribution of seismic sources that effectively surround the receivers. This principle has successfully been exploited to retrieve from recorded passive data more easily usable and interpretable responses. In fact, the retrieval of virtual-source responses has led to a wide range of applications, including for controlled-source seismic surveys. The latter is the case for data-driven methods for redatuming reflection data to a receiver level below the source-acquisition surface, or methods to suppress surface waves in land seismic data. In this thesis, I studied the application of seismic interferometry to surface reflection data, that is, reflection data acquired with both sources and receivers at or near the earth's surface. This is a typical configuration for seismic exploration, either in land or marine surveys. The retrieval of additional virtual sources at receiver locations in that configuration would result in having effectively more shot points. Depending on whether the virtual-source responses contain relevant information, the combined source and virtual-source coverage could allow more complete illumination of the subsurface and so better imaging of its structures. This could be particularly the case for surveys with areas or directions poorly sampled by sources, including large gaps, but with receivers present. The main research questions are what are the conditions for retrieving useful virtual-source reflection responses and with what accuracy. As I first show from mathematical derivations, the retrieval of virtual-source reflection responses from the application of seismic interferometry to exploration-type reflection data does not comply with several theoretical requirements. A major requirement is that the two considered receivers would need to be enclosed by a boundary of sources. This condition is obviously not fullfilled by the single-sided illumination as in exploration surveys. Consequently, as I show using modelled reflection data, the virtual-source reflection responses are retrieved with several distortions, including the presence of undesired non-physical reflection events. Yet, in spite of the non-ideal single-sided configuration, cross-correlating the reflection records at receiver pairs and summing over source profiles allows retrieving virtual-source responses with relevant reflection signals. These virtual reflection signals are referred to as pseudo-physical reflections, as they share the same kinematics as physical reflections but contain distortions due to the {cross-correlation} process. By studying further the numerical examples, I determine the influence of several acquisition-related parameters and subsurface characteristics on the accuracy of the virtual-source reflection responses. Then, based on a theoretical approach using the convolution-type reciprocity theorems, instead of the cross-correlation type, I show how part of the distortions in the virtual-source responses retrieved by cross-correlation could be reduced by performing a multidimensional-deconvolution operation. The potential benefits of multidimensional deconvolution are verified with a numerical example, showing that the obtained virtual-source reflection responses match better the reference physical responses. In addition, I highlight the essential role of the surface-related multiples in the retrieval process of pseudo-physical reflections. In turn, the retrieved pseudo-physical reflections provide usable feedback about the surface multiples. In particular, I present a method based on the stationary-phase analysis of the retrieved pseudo-physical reflection arrivals for detecting surface-related multiple reflections in the acquired data. The results from tests on numerically modelled data show that this interferometric method allows identifying prominent surface multiples in a wide range of source-receiver offsets. Also, I determine that this correlation-based method performs still well even in the case of missing near-offset reflection data. This interesting property suggests that for robust prediction of multiples, the method could be further developed and complement convolution-based schemes which often suffer from missing near-offset data. Still, the main objective in retrieving virtual-source responses is to obtain additional desirable shot points for improving processing or imaging. In general, interpolation techniques are applied to the seismic data to compensate for the irregularities of the acquisition geometry. However, most of the direct interpolation techniques do not allow retrieval of the missing data if the gap is larger than the Nyquist criterion. I show, using numerically modelled datasets, that in these challenging cases, decisive information for imaging may be obtained from the retrieval of virtual sources as long as surface-multiple energy is present in the shot records. In particular, I show that virtual images (obtained from retrieved virtual data) can reveal initially invisible structures in the images obtained from the uncomplete reflection data. Finally, I apply seismic reflection interferometry on a 3D land seismic dataset to test further the practical feasibility of retrieving relevant virtual-source reflection responses. The survey was acquired at a mining site in a hard rock environment with recorded reflections characterized by a relatively poor signal-to-noise ratio. The first results presented in this thesis show evidences of retrieved pseudo-physical reflections. By testing different source contributions, these investigations also show that the retrieval of these desirable events may largely depend on the location and extent of the considered source patch with respect to the virtual source and receiver geometry.@en