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

Abstract

SummaryThis 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 highresistivity 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. Main Objectives:1. Systematically monitor the geophysical responses of clandestine graves over a three-year burial interval. The selected geophysical monitoring methods were electrical (both fixedoffset surveys and electrical resistivity imaging 2D profiles) and multi-frequency GPR surveys.2. To determine, of the geophysical techniques and configurations investigated, which would be optimal to detect buried human remains in the different burial styles (naked and wrapped) and if this changed over time.3. To determine which dominant frequency GPR antennae would be optimal for forensic search teams to utilize for the detection of similar clandestine burials.4. To measure changes in the conductivity of soil-water within a grave, in order to better understand the geophysical survey data collected over the graves.5. To generate and calibrate 2D resistivity models of the survey site at yearly intervals to explain the changing resistivity responses.6. Simultaneously collect appropriate site data (rainfall and temperature) to allow comparisons with other research studies and criminal search investigations. New Aspects Covered:This study is the first to simultaneously collect multi-frequency GPR, fixed off-set and 2D ERI electrical surveys, grave 'leachate' conductivity measurements and site-specific factors (local climate, moisture content, porosity) etc over a three-year monitoring period. Results show surprising variations both temporally and seasonally, with winter surveys consistently

Collaborative Geophysical Monitoring of Simulated Forensic 'Crime Scenes’ in the U.K.

“…These have been repeatedly geophysically surveyed by fixed-offset electrical and Electrical Resistivity Imaging (ERI) surveys as well as multi-frequency (110-900 MHz) GPR datasets at least quarterly, and every month in the first three years post-burial. Studies have been published on determining what causes relative resistivity anomalies [19], magnetic surveys [20], measurements of decompositional fluid conductivities over time [3] as well as the 0-3 years post-burial datasets [6]. Repeat surveys suggest winter surveys are optimal and resistivity surveys should be undertaken six months to two years post-burial for optimal success.…”

“…Geoscientific methods are being increasingly utilised by forensic search teams for the detection and location of clandestinely buried material [4][5]. In the search for clandestine graves of murder victims, burials are usually shallow (less than 3 m and typically 0.5 m below ground level or bgl [6]), but current detection rates are low and, without locating the victim's body, obtaining a successful conviction can be very difficult [1,2]. Search investigators will use a variety of proved methods, which include scenariobased, feature focused, intelligence-led and systematic Standard Operating Procedures [1,2].…”

“…Research using simulated clandestine grave burials provide critical information on optimal detection method(s), equipment configuration(s), sample point spacings, etc., especially if long-term monitoring are undertaken [6]. Adapted from [4].…”

Optimal Geophysical Techniques and Configurations for Below-Patio Forensic Targets

“…Research into better forensic techniques with GPR has been continually undertaken in recent years with the use of simulated burial and pig cadavers as these are similar in the way they decompose to humans (see, e.g. [6,8,9]). …”

“…[3][4] and for human remains (e.g. [3,[5][6][7][8][9]). [10] conducted a control study with buried weapons and found that electro-magnetic equipment could detect metallic objects buried in a grid distribution in a rural environment.…”