DSpace Communidade:
https://repositorio.ufba.br/handle/ri/2616
2024-03-29T12:42:17ZO papel do oceano na modulação de eventos extremos no Sul/Sudeste do Brasil
https://repositorio.ufba.br/handle/ri/37759
Título: O papel do oceano na modulação de eventos extremos no Sul/Sudeste do Brasil
Autor(es): Oliveira, Gustavo Lauton de
Primeiro Orientador: Lentini, Carlos Alessandre Domingos
Abstract: Understanding the processes responsible for extreme events is crucial for public safety and managing coastal and offshore economic activities. The current scientific comprehension has demonstrated that ocean physics may have a great impact on these phenomena and that examining the ocean input can lead to significant insights into how extreme events evolves. With regard to extreme events in south/southeastern Brazil, there is a high frequency of extratropical cyclones and these frontal systems have been pointed out as the main driver for the development of large wave events (LWEs). Furthermore, the first-ever documented South Atlantic Hurricane (Catarina), which made landfall in southern Brazil, began as an extratropical cyclone. In this study, we apply different methods to give a diagnostic of the contribution of the ocean on both Catarina’s modulation and LWEs. The former by applying the genesis potential index (GPI) to give a quantitative diagnostic of the contribution of the environmental factors known to be linked to tropical cyclogenesis. The latter by coupling in a one-way mode the hydrodynamic model Regional Ocean Modeling System (ROMS) and the wave model Simulating WAves Nearshore (SWAN) to study the effect of currents on LWEs produced under the influence of cyclones. For the study of Hurricane Catarina, results indicate two regions of large positive GPI anomalies: where Catarina (1) developed subtropical cyclone structure and underwent tropical transition, and (2) acquired hurricane status. We also examine the ocean’s potential to sustain tropical cyclone intensification through the ocean heat content (OHC). Although some areas of positive OHC anomalies may have indicated conditions favorable to cyclogenesis, it was not sufficient to explain the main stages of Catarina’s development. On the other hand, the GPI in March 2004 was the highest among March of all years (1990–2019), suggesting that this may be a valid index for obtaining a threshold for tropical cyclogenesis in south/southeastern Brazil. Regarding the five LWEs studied, chosen due to the distinct importance that current-to-wave effects had for the period, the results indicate that the addition of currents on the wave model improved the accuracy of the peaks of significant wave height, generally increasing them (by as much as 27%). The increase in wave height occurred mainly near the shelf edge and slope, where the southwestward-flowing Brazil Current opposes the dominant direction of cyclone-generated waves (usually from S/SE to S/SW). Modulation of wave height by currents in the sub-inertial band explained up to 95% of the total variance of the difference between results with and without ocean currents, and this band was largely related to the Brazil Current. Its near-inertial counterpart explained up to 22% of the total variance and was primarily due to near-inertial currents in the region. This study provides, for the first time, conclusive evidence that wave-current interaction can impact LWEs in south/southeastern Brazil.
Editora / Evento / Instituição: Universidade Federal da Bahia
Tipo: Tese2023-05-10T00:00:00ZProcessamento de dados sísmicos terrestres 3D: novas abordagens e soluções
https://repositorio.ufba.br/handle/ri/36438
Título: Processamento de dados sísmicos terrestres 3D: novas abordagens e soluções
Autor(es): Souza, Wilker Eduardo
Primeiro Orientador: Porsani, Milton José
Abstract: The processing of 3D land seismic data is always a great challenge for the petroleum industry, which constitutes a current, relevant, and open to contributions. Among the main problems in the processing flow, we highlight the static errors, obtaining the velocity field, and attenuation of the ground roll. As a product of this thesis, we developed new methodologies and algorithms that improve the 3D ground seismic processing flowchart and, consequently, the final seismic image.
The first contribution is associated with the definition of picking the first break in 3D ground seismic data using the Dynamic Time Warping (DTW) algorithm. In this step, the DTW algorithm that uses the similarity between seismic traces, calculated from a cumulative cost matrix, identifies the first break in the seismogram based on a seed pre-defined by the analyst.
We applied the method to the Polo-Miranga seismic cube in the Recôncavo Sedimentary Basin and Blackfoot (located in Alberta, Canada). The results were satisfactory for the entire range of offsets of the seismic data. In addition, we performed the statics calculations, and the results proved consistent as they attenuated the temporal distortions present in the seismic traces caused by the topographic and thickness variation of the low-velocity zone.
The second contribution is associated with estimating seismic velocity profiles from the decomposition of slowness profiles using the Exponentially Weighted Moving Average (EWMA) and Singular Spectral Analysis (SSA). We used nine wells to densify the velocity model of the Miranga Pole seismic cube and α = 0.025 for smoothing the slowness profile from the EWMA. We decomposed the slowness curve into three components with the SSA method, using only the first. The results, illustrated in temporal slices of the seismic cube, highlighted an improved resolution of the reflectors and the appearance of new reflections previously masked by the ineffective correction of the normal moveout.
The third contribution is associated with noise attenuation. We developed a method that applies Singular Value Decomposition (SVD) in the time and frequency domain, using multidirectional spatial correlations in cross-spreads for ground roll attenuation. We used the seismic cube Polo-Miranga, due to its orthogonal geometry. Besides attenuating the ground roll, the method preserved, highlighted, and improved the lateral continuity of the seismic reflectors, increasing the signal-to-noise ratio of the data. The results are cross-spreads, inlines, and crosslines of the seismic cube.
Editora / Evento / Instituição: Universidade Federal da Bahia
Tipo: Tese2022-11-18T00:00:00ZInterpretação gravimétrica e magnética da estrutura crustal entre a Província Borborema Meridional Oeste e o Norte do Cráton São Francisco
https://repositorio.ufba.br/handle/ri/36345
Título: Interpretação gravimétrica e magnética da estrutura crustal entre a Província Borborema Meridional Oeste e o Norte do Cráton São Francisco
Autor(es): Oliveira, Vinicius Arimateia Ribeiro
Primeiro Orientador: Dutra, Alanna Costa
Abstract: The Southern Borborema Province and the Northern São Francisco Craton experienced major
tectonic events in the Neoproterozoic Era and their tectonic history is still not completely
clarified due to insufficient geotectonic and geophysical studies. This work aims investigating
the main boundaries of the crustal blocks between the Southern Borborema Province
and the Northern São Francisco Craton for the reconstruction of the tectonic history of this
area. Gravimetric, magnetic, geoid anomaly and elevation data were used to accomplish
the objectives. The lateral extensions of the sources were determined through magnetic
field transformations and the depths were estimated by integrating geoid anomaly and topography
data as well as by An-Euler method. The obtained source depths of less than 1 km
and more than 5 km with structural index 1 to 3 are present in the São Francisco Craton
as in the Borborema cross section and west of the Sergipano belt. The obtained crustal
thickness shows a crustal thinning in the Riacho do Pontal belt with 37.25 km in relation
to the north of the São Francisco Craton, with values ranging from 41.6 km, these results
are in accordance with seismic data. These results were used as a priori information, in
the direct crustal 3D modeling to obtain the density contrast distribution in the subsurface.
The lithosphere-asthenosphere interface (LAB) results revealed culminating values in the
north of the craton reaching 216.0 km. In relation to the Pernambuco-Alagoas domains and
the Sergipe belt, LAB values reach 203.0 to 207.0 km thick. The results of the interpreted
geophysical maps reveal geological structures marked by lineaments with preferential direction
NE-SW, consistent with the features originating from the Brasiliano orogenic event, as
well as the contact boundary between the craton and the Borborema Meridional Province,
and the boundary between the Pernambuco-Alagoas domains and the belt: Sergipano and
Riacho do Pontal. The suture zone was identified from high magnetic signatures.
Editora / Evento / Instituição: Universidade Federal da Bahia
Tipo: Dissertação2022-09-01T00:00:00ZInversão da forma de onda completa com abordagem multiescala usando redes neurais recorrentes
https://repositorio.ufba.br/handle/ri/36246
Título: Inversão da forma de onda completa com abordagem multiescala usando redes neurais recorrentes
Autor(es): Santana, Jorge Luís dos Santos
Primeiro Orientador: Pestana, Reynam da Cruz
Abstract: Seen as a fundamental parameter for a reliable geological image of the subsurface, and
consequent exploratory success, seismic velocity is one of the prerequisites in the seismic
exploration chain. Such velocity relates directly to the construction quality of seismic images
through robust algorithms such as reverse time migration (RTM) or other seismic imaging
techniques. In this work, we use machine learning environments to obtain high resolution
seismic velocity through the full waveform inversion (FWI) technique.
In summary, the FWI technique aims to compare data from real observations with
calculated data obtained through seismic modeling from the solution of a specific wave
equation. The residual of this comparison is minimized and the gradient is used to update,
with an iterative optimization algorithm, the velocity model that at the end of the process
will be able to correspond to the real data. Here we will use a Recurrent Neural Network
(RNN), based on the governing physics (acoustic wave equation), to derive the real data
and the calculated data regarding the direct seismic modeling step, since we will deal with
purely synthetic data. In addition, learning environments, such as Pytorch, provide us with
tools for calculating the gradient (automatic differentiation) and the mini-batch strategy
important in terms of reduction memory and higher processing velocity.
As the FWI is based on the iterative minimization of a cost function between observed
and calculated data, in order to avoid convergence to local minima, we use the multiscale
approach of frequency. In addition, we tested the FWI response when subjected to noisy
observation data and less accurate initial models, and compared it with the inversion response
added to the multiscale approach of frequency technique, to demonstrate the performance
of this approach when it comes to mitigating these limitations.
The results obtained in three sets of data demonstrate the efficiency and applicability of
the technique used in the attempt to obtain high resolution seismic velocity fields.
Editora / Evento / Instituição: Universidade Federal da Bahia
Tipo: Dissertação2022-08-19T00:00:00Z