Numerical Simulation of the Time-domain Electromagnetic Field for Thaw Zone Detection

Permafrost thaw in the Arctic and Northern regions has a great impact on both northern ecosystems and human activities in the region. Therefore, efficient and noninvasive methods of thaw monitoring are of utmost importance. In this paper, we explore the applicability of the near-field electromagnetic pulsed sounding method to the problem of thaw zone detection. We consider several variants of the medium composition: a layered model with a thaw top layer; a permafrost half-space with a vertical well with and without the thaw zone along the wellbore, and examine whether the electromotive force or apparent resistivity curves yielded by the numerical simulation of the pulsed electromagnetic field indicate the effect of the thaw zones. The numerical simulations show that the pulsed electromagnetic sounding setup considered in the paper successfully identifies even relatively thin thaw upper layer, whereas a small thaw zone around the wellbore, or an open wellbore itself, are non-detectable by the surface measurements.