Characterizing the Spatial Variability of Permafrost and Geological Formations Using a towed Transient ElectroMagnetic (tTEM) system.
Abstract
Characterizing the spatial variability of permafrost and geological characteristics is critical to understanding Arctic ecosystem functioning in the context of climate change. Recently, a new high-resolution electromagnetic survey method, the towed transient electromagnetic method (tTEM), has been developed (Auken et al., 2018). This method allows to easily map tens of km in 2D and 3D with an investigation depth of up to 100 m (for resistive environments). However, strong induced polarization (IP) effects often associated with permafrost environments and shallow bedrock complicate the interpretation of the TEM data.
In this study, we present a large-scale data set acquired around Nome, Alaska. The main objective of this study is to understand the permafrost distribution and its evolution across the Seward Peninsula, which is an area of discontinuous permafrost that is rapidly changing. Data were acquired in both winter and summer along 2D and 3D transects, covering more than 200 km. Our initial analysis shows that the data set comprises four types of decay curves (DC): fully positive, fully negative, positive-negative and positive-negative-positive data. The last three DCs are typical for an environment characterized by strong IP effects. To better understand the cause and possible subsurface layering, we employ forward modelling of the tTEM system response. This shows that the data can be explained by a conductive and chargeable overburden, overlying resistive bedrock or permafrost. Based on these results, we chose appropriate starting models to invert the data. We calibrate our results based on numerous borehole logs, ERT surveys, and ground temperature measurements that are available at the study site. Our results show that despite the challenges introduced by the strong IP effects, a tTEM tool is effective for mapping permafrost and bedrock distribution in Arctic environments. Auken, E., Foged, N., Larsen, J.J., Lassen, K.V.T., Maurya, P.K., Dath, S.M., Eiskjær, T.T., 2018. tTEM — A towed transient electromagnetic system for detailed 3D imaging of the top 70 m of the subsurface. Geophysics 84, E13-E22. https://doi.org/10.1190/geo2018-0355.1- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMNS22B0285F