Haroon, Amir , Jegen, Marion , Schwalenberg, Katrin, Weymer, Bradley , Faghih, Zahra and Micallef, Aaron (2019) 2D Inversion of Marine Time Domain CSEM Data: Developments and Application to an Offshore Aquifer Investigation in the Canterbury Basin, New Zealand. [Talk] In: IUGG General Assembly 2019. , 08.-18.07.2019, Montreal, Canada .

Abstract

Time-Domain Controlled Source Electromagnetic (TD-CSEM) methods are commonly applied to detect and delineate sub-surface resistivity anomalies on land and in the marine environment. The most general form of the application utilizes a horizontal electric dipole (HED) current excitation with an alternating current step function ranging from periods of a couple 100 ms to several seconds. TD-CSEM measurements are typically conducted along a transect in a towed inline configuration. Accordingly, the data is mainly sensitive to resistivity variations located between the source and the receiver. Therefore, 2D inverse modelling is often considered sufficient to adequately represent the measured data in regions of simple geometry/bathymetry. Although recording of TD-CSEM data is quite sophisticated in terms of instrumentation, the interpretation in academia is still based on simplified assumptions of 1D resistivity models that may fail to represent the true resistivity distribution of the sub-surface. Here, we present a development of the freely available frequency-domain code MARE2DEM, which now allows the inversion of TD-CSEM data. The theoretical code developments are tested in terms of comparative 2D forward modelling studies and have been applied to an offshore groundwater investigation from the Canterbury Basin, New Zealand. 2D inversion models from almost 300 km of data collected are presented and compared to stitched 1D inversion models. Overall, the 2D inversion models offer a more complete picture of the subsurface resistivity distribution and allow to map the lateral extent of the aquifer across the basin.

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