Seismic depth imaging of sea-level controlled depositional sequences at the New Jersey shelf

Abstract

This master thesis is part of a joint project carried out at TU Bergakademie Freiberg and RWTH Aachen University, aspiring to simulate numerically the fresh water emplacement and recharge system at the New Jersey shelf. Analyses of data, acquired during the most recent seismic drilling campaign IODP Leg 313 at the New Jersey shelf, revealed complex salinity variations with depth (Lo et al., 2013). Additionally, fresh water reservoirs with a salinity lower than 3 g/L have been discovered down to 400 m depth below the sea floor and up to 130 km far-off the New Jersey coast (Mountain et al., 2010; Post et al., 2013). The origin of the freshwater distribution so far-off the New Jersey coast is still unknown, leading to an ongoing debate over two conflicting hypotheses. It is the main objective of the joint research, to achieve a better understanding of these vertical salinity variations and the controlling factors of groundwater circulation at the NJ shelf. Re-processing and depth imaging of the available seismic data are necessary for deriving a reliable 3D subsurface model to be further applied for numerical flow and transport simulations. During this master thesis, the seismic profile line Oc270_029 was primarily re-processed in the time domain. Following the steps of pre-processing, a Kirchhoff pre-stack time migration approach was executed, resulting in an enhanced time-migrated image. On the base of this time-migrated section, horizon interpretation was performed to proceed with the depth imaging of the seismic data. As a first step, an interval velocity model was derived as a function of depth by standard semblance analysis of the seismic data. This velocity model was used in a Kirchhoff pre-stack depth migration, resulting in a first subsurface model. Subsequently, the velocity model was refined by horizon- and grid based tomography approaches and an updated Kirchhoff prestack depth migration result was calculated using this new velocity models. Interpretation of previously identied sequences by Miller et al. (2013a) on the depth-migrated stack of Oc270_029 is concluding this thesis.