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An integrated approach to assess slope instability offshore Espírito Santo, SE Brazil

Piedade, Aldina 2016. An integrated approach to assess slope instability offshore Espírito Santo, SE Brazil. PhD Thesis, Cardiff University.
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Abstract

This thesis uses a three-dimensional (3D) seismic reflection data from the continental slope of the Espírito Santo Basin (SE Brazil) to investigate, at first, the prolonged halokinesis on raft tectonics and its effect on the surrounding structures and how these can affect the post-raft overburden units. Secondly, the high-quality 3D seismic dataset was the source of information to characterise, describe and model a set of mass-transport deposits (MTDs). Their morphology and kinematic factors are described using a geomorphological approach. The main research hypothesis for this thesis are i) how the salt and raft tectonic are acting on the continental slope of Espírito Santo Basin and how is their influence in the post raft overburden? ii) which are the most common typology of MTDs in the study area and is it possible to related their morphometric and kinematic attributes with the slope geomorphology where the MTDs occurred?, and iii) is it possible applying a bivariate statistic method, already tested on onshore slope instability, to understand the natural conditions for the occurrence of MTD in the study area? The Espírito Santo Basin is characterised by halokinesis where the Aptian salt has been withdraw into salt structures through time (e.g. diapirs, rollers and pillows). This process leads to complex raft deformation, which occurs in different forms as documented in this thesis. The salt and raft tectonics triggered faults that strongly influenced the post-raft overburden units and later induced the remobilisation of sediment near the seafloor. The second analysis in this thesis is focused on the characterisation of MTDs. The 3D seismic data were the main source of information integrated into Geographic Information Systems (GIS) in order to compute a set of morphometric attributes to characterise the MTDs and the depositional surface which underlie them. At first, two different MTDs were identified and described; Confined and Unconfined. The inclusion of local topography in the studies to the occurrence of MTDs, as investigated in this part, is a new approach in submarine slope instability studies, and local topography was found to constrain the run-out distance of the MTDs. Abstract 2 Finally, the thesis aimed to understand the natural conditions favourable to the occurrence of MTDs in the study area. Seven predisposing factors were computed from the topographic layer, or depositional surface as named in this thesis. The spatial integration of the predisposing factors with the inventory was based on a statistical bivariate method (Informative Value). The results were validated and the predisposing factors were ranked according to their contribution to MTDs’ spatial distribution, allowing for the computation of a sensitivity analysis. The best Area Under the Curve (AUC) was recorded by model 3 (AUC = 0.862). The results of this thesis are important for both hydrocarbon exploration and academia. From the exploration point of view, the information given in the first data chapter contributes to the understanding of raft and salt tectonics as a trigger of reservoir compartmentalisation. The second analysis provides valuable techniques and methodologies that combine seismic datasets and GIS, used in the last section to calculate favourability scores as a further step for offshore hazard assessments. From an academic point of view, this thesis comprises a timely test of how methods and techniques applied in onshore analysis apply to offshore environments.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Date of First Compliant Deposit: 19 August 2016
Last Modified: 20 Jul 2017 04:55
URI: http://orca.cf.ac.uk/id/eprint/93847

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