Author: Andrew Frost
Frost, Andrew, 2025 Assessing a multi-method geophysical approach in the locating of unmarked graves under various seasonal conditions., Flinders University, College of Humanities, Arts and Social Sciences
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This research used known burial sites to ascertain if there is an optimal seasonal time to conduct geophysical surveys to locate unmarked graves. This is important research as this was the first known study undertaken by the person who dug the graves in one study site, the certainty that there was no other anthropogenic interference between the burials. Also using known burials, of recent age, has firmly established the effectiveness of the chosen geophysical methods. This research is important to carry out in a South Australian context, as much of the research found in the literature is focused on climates that experience significantly more rainfall than South Australia.
My original contribution to knowledge is that in the soils typical of South Australia, it is the complexity of the soils physical and chemical characteristics that governs the effectiveness of geophysical methods in detecting human burials. Further to this I state that in the soils of South Australia, the relationship between soil moisture, radar velocity and resistivity are not linear relationships. As an addition to these points, I add to current knowledge in the discipline of Archaeology, that resistivity methods are slightly more effective in detecting burials in higher conductivity soils, as well as contributing my results of pXRF and Magnetic Susceptibility to the knowledge bank.
Burials are ubiquitous in the archaeological and forensic record, and the reliable detection of graves is an important challenge facing community groups, industry and law enforcement. Community groups and cemetery authorities look for reliable and cost-effective methods to help locate older burials and find space in ever filling burial grounds. Law enforcement authorities need rapid search methods and assurance that the conditions will not degrade the results. Locating burials sites is important as human remains occupy a unique position in an archaeological context, that being both a biological and cultural entity, able to connect contemporary society to a time and place from the past. Analysis of a burial using cross-disciplinary methodologies can allow revelation of many sophisticated sociocultural aspects of the past, these aspects can include social structure, population histories, diet and health, ritualized practices, as well as migrations and cosmologies
Geophysical methods are often used to locate unmarked graves due to their non-invasive nature and rapid site coverage, however, there are many factors that can influence, positively and negatively, the gathering, processing, and interpretation of geophysical data.
By using the same equipment over the life of this research, as well as a somewhat standard data process flow, the focus will be firmly on the subsurface matrix, how the soil and seasonal subsurface moisture levels affect the ability of these two geophysical methods in the pursuit of locating unmarked graves.
The two geophysical methods discussed within this study are active methods and so generate a signal (electrical and electromagnetic) that passes through the subsurface profile. Changes in these signals are then recorded. It can be seen then that the freedom and ease of these signals to pass through the subsurface profile is of paramount importance. The archaeological remains that are the targets of geophysics are typically in the subsurface profile, and because of this, the subsurface environment has a large influence on the effectiveness of these methods, due to changes in temperature, moisture levels, and soil type, to name a few.
The study sites are chosen as they offer the optimal above ground conditions, tended lawn as a ground cover, no grave furniture to impede the geophysical methods, and known burials. The lithologies presented at these sites are varied, so do offer contrast.
The subsurface matrix is a complex environment, this inhomogeneous nature of the subsurface matrix causes soil particles to be in contact with a variety of surfaces, these can be either permanently or variably charged. This then is a real soil system and is not simply composed of mixtures of pure minerals, but of materials covered with a variety of organic and inorganic films and coatings often bonded together into aggregates by various cementing agents. Subsurface soil moisture is the focus of much discussion in the literature. This subsurface soil moisture is largely dependent on naturally occurring precipitation, and so the relationship between the geophysical method and the soil structure will be examined to determine if there is an optimal time after these precipitation events that the geophysics can be conducted.
Using known graves will give instant feedback, with the potential for all burials to be identified with both geophysical methods. The results will be presented as a percentage of burials detected, the changes in radar velocity plus the changes in resistivity are compared to the seasonal precipitation recorded in previous days.
Keywords: unmarkerd graves, Ground Penetrating Radar, Electrical Resistivity Tomography, geophysics, burials
Subject: Archaeology thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Humanities, Arts and Social Sciences
Supervisor: Prof Ian Moffat