Time-Lapse Electrical Resistivity Tomography Imaging of Buried Human Remains in Simulated Mass and Individual Graves

Abstract

Electrical resistivity has been used as a noninvasive geophysical technique for locating clandestine graves and monitoring human decay within the subsurface. Detailed studies assessing resistivity anomalies due to soil disturbances and decay products associated with graves have relied on the use of proxies, such as pigs, with limited studies using real human cadavers and simulating a mass grave setting and none assessing the anomalies in 3D. In this study, we used time-lapse 2D and quasi-3D electrical resistivity distribution measured over an experimental mass grave and individual graves containing human cadavers to assess resistivity anomalies resulting from graves and the presence of decaying human remains in them. This study is part of a novel multidisciplinary mass grave experimental study with six graves consisting of a mass grave with six human cadavers, a controlled mass grave with none, three individual graves with one human cadaver each, and a control individual grave with none. Nine parallel resistivity transects which allow us to image these graves in their 3D context were acquired prior to excavation and 2 days, 1, 2, and 6 months after burial using a dipole–dipole electrode array, a unit electrode spacing of 0.5 m, and an interprofile spacing of 1m. The value of different electrode arrays and spacings in identifying the contrast between the graves was also assessed using forward models and field data. Soil sensors were installed at different locations in the graves to monitor soil electrical conductivity, moisture content, and temperature. The results of this study show an increase in electrical resistivity 2 days after burial in all graves with human remains and the control graves, which we attribute to increased soil aeration where disturbed pores are filled with air. The resistivity decreases thereafter in graves with human remains which we attribute to the formation of conductive leachates. This study validates the potential of electrical resistivity as a forensic search tool for locating both clandestine mass and individual graves and as a noninvasive monitoring technique to support human decomposition research.

Using geophysics to guide the selection of suitable sites for establishing sustainable earthen fishponds in the Niger-Delta region of Nigeria

“…In this study, we used one-dimensional (1D) and two-dimensional (2D) distributions of electrical resistivity and induced polarization with soil cores to estimate the stratigraphic variations at the study sites. Electrical resistivity involves the injection of electrical current (I) using a pair of source electrodes and measuring the resulting potential difference (V) using other electrode pairs, while the resistivity (ρ) is estimated using Ohm's law and accounting for the electrode arrangement [ 37 , 53 ]. Induced polarization involves measuring the reversible charges stored in a porous medium using similar electrode pairs used in electrical resistivity [ 37 ].…”

“…To minimize data error, a current injection of 1.00 mA was done with a minimum and maximum injection cycle of 3 and 6 following standards described in Ref. [ 53 ]. We used the reversed quadrupole measurement to assess the accuracy and rejected measurements with over 10% deviation.…”

Soil and groundwater contamination by crude oil spillage: A review and implications for remediation projects in Nigeria

“…Geophysical approaches have been demonstrated to be effective in contaminated site characterization and monitoring as they provide quantitative information on the contaminant flow process in both saturated and unsaturated media (Major et al, 2014). In addition, the geophysical technique is sensitive enough to detect biogeochemical changes caused by degradation and redox reactions, making it useful for environmental monitoring (Doro et al, 2022b). The use of electrical resistivity tomography to determine the spatial distribution of hydrocarbon pollution has received much attention (Mao et al, 2016).…”

Combining geophysical and geological datasets to improve a conceptual aquifer model of the Oak Openings Region in northwest Ohio, USA

“…Electrical resistivity involves injecting direct current or low-frequency alternating current into the ground using a pair of electrodes and measuring the resulting potential difference using a second pair of electrodes. The electrical resistivity is computed as a product of the measured potential difference normalized by the injected current and the electrode con guration factor, which depends on the arrangement of the current and potential electrode pairs (Binley and Slater, 2020;Doro et al, 2022). Theoretical details of the method are discussed in Binley and Slater (2020) and Everette (2013).…”

“…2B). In contrast to the 1-D ES, a dipole-dipole electrode array was chosen for the 2-D data acquisition for its good trade-off of sensitivity and the possibility of using all 8 channels simultaneously to reduce the data acquisition time (Doro et al, 2022). A 2 m unit electrode spacing gives a pro le length of 166 m for each transect, while other measurement settings are similar to that of the 1-D survey.…”