Faghih, Zahra , Jegen, Marion , Haroon, Amir , Berndt, Christian , Gehrman, R., Micallef, Aaron and Schwalenberg, K. (2022) Geophysical and Core Data Integration to Characterise and offshore Freshened Groundwater System in the Canterbury Bight. [Talk] In: 83. EAGE Annual Conference & Exhibition Workshop Programme. , 06.-09.06.2022, Madrid, Spain . DOI 10.3997/2214-4609.202211048.

Abstract

Offshore groundwater systems have been suggested as alternative sources of potable water in islands and coastal regions. In this study, we integrate offshore controlled-source electromagnetic (CSEM) with borehole data to identify an offshore groundwater system in the Canterbury Bight, New Zealand. CSEM data were acquired with a seafloor-towed system along four profiles and 2-D inversion was carried out using MARE2DEM to derive resistivity models along each profile. Moreover, a trans-dimensional Bayesian inversion was conducted to assess the distribution of plausible resistivity-depth models. The study area was previously investigated during IODP Expedition 317 in which a pore-fluid salinity anomaly (24 psu at 40 mbsf) was recorded in borehole U1353. A comparison between the CSEM resistivity model and the resistivity-depth profile converted from pore-water salinity within the borehole shows a strong correlation between CSEM and borehole data at the closest waypoint to site U1353. We show through a Markov-Chain Monte Carlo approach that our estimates of seafloor resistivity agree with the measured borehole data. The computed resistivity distributions at the borehole provide significant evidence that the CSEM inversion models can be used to extrapolate groundwater inferences from the borehole onto a basin scale providing improved geophysical imaging capabilities for offshore freshened groundwater.

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