Electrical resistivity tomography of simulated graves with buried human and pig remains

Rigorous field assessment in different soil types and climates comparing simulated graves with pig remains and human remains are needed to assess the capabilities and limitations of electrical resistivity tomography (ERT) as a tool to search for unmarked graves. Our study assesses the ERT signals from graves with pig and human remains in a cold, humid continental climate with sandy soils. Two sets of three experimental graves were established: the first set consisted of two graves containing human remains and an empty grave serving as a control, while the second set consisted of two graves with pig remains and a second empty grave. ERT measurements were conducted prior to establishing the graves and were repeated 10 times over seventeen months, except for winter months when measurements were impossible. Each time we acquired eight 18 m long ERT transects using a dipole-dipole electrode array with a unit electrode spacing of 0.5 m and the transects spaced 1 m apart. The measured electrical resistivity decreased for all graves by 14-22 % for measurements conducted up to two months after burial. No further decrease was observed in the control, while resistivity in the graves with human and pig remains continued to decrease by 45-52 % up to the end of our study, seventeen months after burial. The resistivity anomaly in the pig graves shows a contrasting anomaly that is broader than that of the human remains. Our study thus validates the sensitivity of ERT to graves in cold, humid climates with sandy soil.