Assessing changes in electrical resistivity signals in simulated mass and single graves over 18 months after burial

Abstract

Electrical resistivity tomography (ERT) has been increasingly explored as a non‐destructive technique for searching for unmarked graves. However, its effectiveness remains uncertain as measured resistivity responses are influenced by burial type, time after burial, soil properties and environmental conditions. Previous studies have reported both positive and negative resistivity anomalies associated with graves, highlighting the need for further controlled investigations. Moreover, limited experimental data exist for ERT measurements over graves containing human cadavers and for mass graves, despite their relevance to forensic and humanitarian investigations. Hence, this study assessed ERT signals associated with individual and mass graves with human cadavers over 18 months post‐burial. We established two mass graves, with one containing six commingled human cadavers and the second containing none serving as a control. Four individual graves were also established, with three containing one cadaver each and the fourth as control. We conducted ERT measurements before establishing the graves and at seven selected intervals after burial. The data were acquired across nine transects spaced every 1.0 m with 0.5 m electrode spacing and a dipole–dipole array. This produced repeated 2D ERT profiles across the graves which we combined in a 3D inversion to obtain quasi‐3D images. We assessed the effects of different electrode arrays and spacings on resolving the graves. The graves showed up to a 70% increase in resistivity ∼3 days after burial, and the resistivity decreased afterward to a minimum at ∼185 days after burial with lower resistivities in the mass grave. The dipole–dipole array and 0.5 m electrode spacing were the most efficient in resolving the graves. The 3D ERT images also captured the outline and depth of the graves. This study validates the use of ERT as a search tool for unmarked graves, particularly mass graves, which produced stronger resistivity contrasts.