John R. Jervis

Time-Lapse Geophysical Investigations over a Simulated Urban Clandestine Grave

Abstract:  A simulated clandestine shallow grave was created within a heterogeneous, made‐ground, urban environment where a clothed, plastic resin, human skeleton, animal products, and physiological saline were placed in anatomically correct positions and re‐covered to ground level. A series of repeat (time‐lapse), near‐surface geophysical surveys were undertaken: (1) prior to burial (to act as control), (2) 1 month, and (3) 3 months post‐burial. A range of different geophysical techniques was employed including: bulk ground resistivity and conductivity, fluxgate gradiometry and high‐frequency ground penetrating radar (GPR), soil magnetic susceptibility, electrical resistivity tomography (ERT), and self potential (SP). Bulk ground resistivity and SP proved optimal for initial grave location whilst ERT profiles and GPR horizontal “time‐slices” showed the best spatial resolutions. Research suggests that in complex urban made‐ground environments, initial resistivity surveys be collected before GPR and ERT follow‐up surveys are collected over the identified geophysical anomalies.

Electrical resistivity survey to search for a recent clandestine burial of a homicide victim, UK

This case report details an electrical resistivity survey to assist the search for a suspected 1-year-old clandestine burial of a murder victim in North Wales in the UK. Conventional search techniques (victim recovery dogs and probing) proved unsuccessful, and with a significant survey area and a high clay content soil precluding GPR as a geophysical search method, a resistivity survey was instead trialled. Ten resistivity grids were collected and site detrended with user-specified, contoured anomalies being generated. The resulting anomalies were compared to anomalies derived from similar-aged, simulated clandestine burial surveys. Seven anomalies with comparative sizes and amplitudes (±3Ω) of the simulated burials were identified within the search area and prioritised for further investigation. The shallowly buried victim was subsequently recovered outside the survey area.

Geophysical Monitoring of Simulated Clandestine Graves Using Electrical and Ground-Penetrating Radar Methods: 0-3 Years After Burial

Abstract:  This study provides forensic search teams with systematic geophysical monitoring data over simulated clandestine graves for comparison to active cases. Simulated “wrapped” and “naked” burials were created. Multigeophysical surveys were collected over a 3‐year monitoring period. Bulk ground resistivity, electrical resistivity imaging, multifrequency ground‐penetrating radar (GPR), and grave and background “soil‐water” conductivity data were collected. Resistivity surveys revealed the naked burial had consistently low‐resistivity anomalies, whereas the wrapped burial had small, varying high‐resistivity anomalies. GPR 110‐ to 900‐MHz frequency surveys showed the wrapped burial could be detected throughout, with the “naked” burial mostly resolved. Two hundred and twenty‐five megahertz frequency GPR data were optimal. “Soil‐water” analyses showed rapidly increasing (year 1), slowly increasing (year 2), and decreasing (year 3) conductivity values. Results suggest resistivity and GPR surveys should be collected if target “wrapping” is unknown, with winter to spring surveys optimal. Resistivity surveys should be collected in clay‐rich soils.

Time-lapse resistivity surveys over simulated clandestine graves

The aim of this study was to develop a better understanding of how electrical resistivity surveys can be used to locate clandestine graves. Resistivity surveys were conducted regularly over three simulated clandestine graves containing a pig cadaver, no cadaver and a pig cadaver wrapped in tarpaulin, respectively. Additionally, soil and groundwater samples were collected from two more simulated graves outside the survey area. The grave containing a pig cadaver was detectable from a low resistivity anomaly in the survey data. Groundwater data suggest that the resistivity anomaly associated with the surveyed pig grave was caused by a localised increase in groundwater conductivity. Wrapping a cadaver was found to initially change the resistivity response of a grave to a high resistivity anomaly. Resistivity surveys did not detect the disturbed soil in the grave that did not contain a cadaver. Although soil samples showed grave soil to be more porous than undisturbed soil, the lack of response from the grave that did not contain a cadaver suggests that disturbed soil was not responsible for the resistivity anomalies observed in this study. Resistivity surveys successfully detected all graves containing cadavers throughout the study, whilst also showing the potential to eliminate the need for mass excavation in a genuine search.

Comparisons of magnetic and electrical resistivity surveys over simulated clandestine graves in contrasting burial environments

Determining the effectiveness and limitations of near-surface, non-invasive geophysical techniques is imperative when attempting to locate clandestine burials. Unlike in archaeology, there has been limited forensic research with regard to optimum methodologies, with most emphasis to date being on metal detectors and ground-penetrating radar. However, these techniques may not be suitable in certain soil types (e.g., conductive or highly magnetic) or for certain non-metallic targets. Therefore, in this study, magnetic and electrical resistivity detection techniques have been utilized over different aged (0.25–1 year) simulated clandestine burials with no buried metal, in contrasting depositional environments. These environments included semi-rural, urban, woodland and a parkland medieval grave site acting as an archaeological analogue. The magnetic surveys showed mixed success in detecting clandestine burials. Elevated magnetic gradient readings, with respect to background values, were observed over very shallow burials, whereas deeper burials displayed a reduction in gradient and/or no associated magnetic anomalies. Magnetic anomalies were observed over surface-burials and validated by simple 2D forward modelling. Magnetic anomalies were also observed in the control data set. Electrical resistivity surveys produced anomalies over all the simulated burial positions, including surface burials but did not produce anomalies at the archaeological analogue site. Laboratory analysis of fluid retrieved from simulated graves showed an overall increase in iron levels over a year post-burial, which may account for the observed magnetic anomaly variation. There was also a corresponding increase in grave ‘fluid’ conductivity, which was interpreted to be the cause of the observed low resistivity anomalies. This research suggests that, as a technique for locating clandestine burials, bulk ground resistivity is more successful than the tested magnetic methods. Moreover, magnetic techniques are more effective when used as part of a multi-technique study over rural and semi-rural sites that are relatively low in magnetic and electrical ‘noise’. These results have important implications for the use of geophysical techniques when searching for clandestine burials. We emphasize that local depositional environment, soil type, likely style of burial and search area size should all be considered when choosing forensic geophysical detection techniques. We also provide evidence to show that geophysical data can assist in locating a primary deposition site even when no physical evidence remains.

Using Soil and Groundwater Data to Understand Resistivity Surveys over a Simulated Clandestine Grave

Geophysical electrical resistivity surveys have been used in a number of attempts to locate clandestine ‘shallow’ graves, based on the valid assumption that a grave may represent a contrast in the electrical properties of the ground compared to ‘background’ values. However, the exact causes of measurable geophysical signals associated with graves are not well understood, particularly for electrical methods. In this study, soil and groundwater samples have been obtained from a simulated grave containing a domestic pig (Sus domestica) carcass, in order to better understand how the presence of a grave may influence the bulk electrical properties of the soil. This information is used to explain observations based on repeat resistivity surveys over a period of 6 months over a second simulated grave at the same site. An area of low resistivity values was observed at the grave location in the survey data obtained from 4 to 20 weeks post-burial, with the grave being difficult to identify in survey data collected outside of this interval. The low resistivity grave anomaly appeared to be caused by highly conductive fluids released by the actively decomposing carcass and this is consistent with the relatively short timescale during which the grave was detectable. It is then suggested that the most appropriate time to use resistivity surveys in the search for a grave is during the period in which the cadaver is most likely to be undergoing active decomposition. However, other authors have observed low resistivity anomalies over much older graves and it is possible that, for graves in different environments, other factors may contribute to a detectable change in the bulk electrical properties of the soil.

Long‐term Geophysical Monitoring of Simulated Clandestine Graves using Electrical and Ground Penetrating Radar Methods: 4–6 Years After Burial

This ongoing monitoring study provides forensic search teams with systematic geophysical data over simulated clandestine graves for comparison to active cases. Simulated “wrapped,” “naked,” and “control” burials were created. Multiple geophysical surveys were collected over 6 years, here showing data from 4 to 6 years after burial. Electrical resistivity (twin electrode and ERI), multifrequency GPR, grave and background soil water were collected. Resistivity surveys revealed that the naked burial had low‐resistivity anomalies up to year four but then difficult to image, whereas the wrapped burial had consistent large high‐resistivity anomalies. GPR 110‐ to 900‐MHz frequency surveys showed that the wrapped burial could be detected throughout, but the naked burial was either not detectable or poorly resolved. 225‐MHz frequency GPR data were optimal. Soil water analyses showed decreasing (years 4 to 5) to background (year 6) conductivity values. Results suggest both resistivity and GPR surveying if burial style unknown, with winter to spring surveys optimal and increasingly important as time increases.

Soilwater conductivity analysis to date and locate clandestine graves of homicide victims

In homicide investigations, it is critically important that postmortem interval and postburial interval (PBI) of buried victims are determined accurately. However, clandestine graves can be difficult to locate; and the detection rates for a variety of search methods (ranging from simple ground probing through to remote imaging and near‐surface geophysics) can be very low. In this study, simulated graves of homicide victims were emplaced in three sites with contrasting soil types, bedrock, and depositional environments. The long‐term monthly in situ monitoring of grave soil water revealed rapid increases in conductivity up to 2 years after burial, with the longest study evidencing declining values to background levels after 4.25 years. Results were corrected for site temperatures and rainfall to produce generic models of fluid conductivity as a function of time. The research suggests soilwater conductivity can give reliable PBI estimates for clandestine burials and therefore be used as a grave detection method.

Comparison of Time-lapse GPR and Resistivity over Simulated Clandestine Graves

Forensic geophysics should be an invaluable tool to assist search teams to detect and locate clandestine graves of buried murder victims. At present however, geophysics is under-utilised and currently used techniques may not be optimal for specific targets or sites. There is a need for geophysical datasets to be collected over known burial sites for varying time periods post-burial. A study site was created with a naked and wrapped pig cadaver. The dimensions are based on available statistics of discovered burials. Monthly surveys using resistivity, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were performed post-burial. Resistivity results show low anomalies over the naked pig and a smaller high anomaly over the wrapped pig with respect to background values. ERT time-lapse data shows optimum survey periods for the naked and wrapped pigs to be 9 and 3 months respectively. GPR 2D profiles detected both burials, with the wrapped pig exhibiting stronger reflection events. Lower frequency (110 MHz) antennae were found to be the optimal frequency to detect pig burials.

Geophysical Monitoring of Simulated Clandestine Graves Using Electrical and GPR Methods - 0-3 Years after Burial

This study provides forensic search teams with systematic geophysical monitoring data over simulated clandestine graves for comparison to active cases. Simulated ‘wrapped’ and ‘naked’ burials were created. Multi-geophysical surveys were collected over a three-year monitoring period. Bulk ground resistivity, Electrical Resistivity Imaging, multi-frequency Ground Penetrating Radar and grave ‘soil water’ conductivity data were collected. Resistivity surveys revealed the naked burial had consistently low-resistivity anomalies, whereas the wrapped burial which had small, varying high-resistivity anomalies. GPR 110-900 MHz frequency surveys showed the wrapped burial could be detected throughout, with the ‘naked’ burial difficult to resolve after 18 months. 225 MHz frequency data was optimal. ‘Soil water’ analyses showed rapidly increasing (year one), slowly increasing (year two) and decreasing (year three) conductivity values. Results suggest resistivity and GPR surveys should be collected if target ‘wrapping’ is unknown, with winter to spring surveys optimal. Resistivity surveys should be collected in clay-rich soils.