A ground penetrating radar (GPR) survey at Fort VII in Kaunas, Lithuania has aided in locating a Jewish mass grave from the Holocaust. The discovery of human remains near the eastern wall of Fort VII prompted the Lithuanian government and Jewish Community to invite an international team of students, archaeologists and geophysicists to conduct GPR and electrical resistivity tomography (ERT) surveys to determine the graves definite existence and size in July of 2017. Using 225 and 500 MHz antenna with a respective step size of 0.1m and 0.02m, two grids measuring 16m × 8m and 12m × 7m with lines spaced every quarter meter were collected on the suspected location of the mass grave. GPR datasets were processed using the GFP_Edit and EKKO_Project programs. Results showed the existence of a pit shaped feature measuring 10m × 8m at a depth of 0.2m to 0.8m in both of the grids. Analogous dimensions of the feature within the two collected grids coupled with historic data surrounding the grave's location and size, preliminary GPR investigation of the site is highly encouraging in determining the grave's parameters. This data can then be used to create a perimeter around the suspected location of the mass grave to ensure the grave will not be disturbed again in the future.
Apparent electrical conductivity maps produced from frequency-domain airborne electromagnetic (AEM) surveys often show an incomplete picture of subsurface conditions and require inversion to fully understand the 3-D geometries of geological layers and potential groundwater plumes. However, even unconstrained inversions can lead to ambiguous results. A constrained inversion using borehole lithologies and ground-based geophysics data as gradient reference and parameter reference constraints provides a more refined model, enabling higher confidence in the interpretation. The purpose of this study was to test the effectiveness of a ground-based geophysics field program utilizing electrical resistivity tomography (ERT) and geophysical borehole logging to constrain a RESOLVE AEM data inversion in order to triage potential groundwater salinity plumes from electrically conductive lithologies at a potash mine, located in Saskatchewan, Canada. Note: This paper was accepted into the Technical Program but was not presented at IMAGE 2021 in Denver, Colorado.
An understanding of the characteristics of fault zones which produce infrequent large earthquakes is essential for seismic hazard and risk assessment. In an attempt to supplement palaeoseismic methods and determine the structure of active faults in the deeper subsurface, we have acquired and processed ground-penetrating radar (GPR) data (up to 20m depth) and high-resolution seismic reflection data (several hundred metres to 1km depth) across three major fault systems located on the South Island of New Zealand. The seismic and GPR data are subjected to a wide variety of processing schemes, generating clear and vivid images of all target structures. The Alpine Fault is constrained to be steeply dipping, with a ~35 m vertical offset of the late Pleistocene erosional basement surface. The Canterbury Plains data show that basement and Cretaceous-Tertiary layers have been intensely thrust faulted and folded, and in addition, display evidence of gentle folding and disruption in some of the overlying Quaternary layers. The Ostler Fault Zone data show a main fault strand dipping at ~50°, with significant off-fault subsidiary faulting and folding and strong lateral variation along strike.
Abstract. The different types of geological deposits and rock formations found in alpine watersheds play key roles in regulating the rate and timing of runoff to mountain rivers. Talus and alpine meadows are dominant features in these areas, but scant data exist for their capacity to store and transmit groundwater. To gain further understanding of these processes, we have undertaken a combined geophysical and hydrological study of a small (2100 m2) alpine meadow and surrounding talus within the Lake O'Hara watershed in the Canadian Rockies. Several intersecting ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) profiles and a seismic refraction profile were acquired to map the thickness of the talus and to image the topography of the bedrock basin that underlies the meadow. From analysis of the GPR and seismic profiles, we estimate that the talus deposits are relatively thin (<6 m). Combined interpretations from the GPR and ERT data show that the fine-grained sediment comprising the meadow basin has a total volume of ca. 3300 m3 and has a maximum thickness of ca. 4 m. Annual snow surveys and stream gauging reveal that the total input volume of snowmelt and rainfall to the meadow basin is several times larger than its groundwater storage capacity, giving rise to low total-dissolved species concentrations (14–21 mg/L) within the meadow groundwater. Observations from four piezometers established on the meadow show that the water table fluctuates rapidly in response to spring snowmelt and precipitation events but otherwise maintains a relatively stable depth of 0.3–0.4 m below the meadow surface during summer months. A slug test performed on one of the piezometers indicated that the saturated hydraulic conductivity of the shallow meadow sediments is 2.5×10−7 m/s. We suggest that a bedrock saddle imaged underneath the southern end of the meadow forms a natural constriction to subsurface flow out of the basin and helps to maintain the stable water-table depth.
In Western Canada, oil and natural gas pipeline projects are being considered that will move hydrocarbons from the Prairie Provinces and British Columbia, to the Pacific Ocean, the Atlantic, and even potentially the Arctic. Along the proposed right-of-ways, the pipeline engineers will encounter challenging and varied terrain, including discontinuous permafrost, creek and river crossings, glaciomarine clays, thick muskeg, and other subsurface conditions that require specialized engineering planning in advance of construction. Geophysical surveys, in support of geotechnical investigations, provide continuous subsurface information to help inform design challenges associated with the many terrain challenges. Some geophysical surveys to be considered include electrical resistivity tomography (ERT), induced polarization (IP), seismic refraction, seismic reflection, multi-channel analysis of surface waves (MASW), ground penetrating radar (GPR), and borehole geophysics. Typically, a combination of several geophysical surveys along with drilling information, are optimal for the cost-effective site characterization of problematic segments of proposed pipeline right-of-ways.
Archaeological site investigations in urban environments are often beset with challenges such as (1) an absence of buried artifacts due to recent disturbance from infrastructure development or (2) community concerns about potential site impacts from excavations. Noninvasive geophysical surveys that use a combination of methods can help mitigate the risks of uncertain outcomes by identifying areas where culturally significant features are more likely to be uncovered. We show how new technology and traditional geophysical survey methods were used to characterize the subsurface of the Mila 18 Memorial site in Warsaw, Poland. This site is one of the most important places of remembrance for the Holocaust and coincides with the location of an underground bunker that was used by Jewish resistance groups during the 1943 Warsaw Ghetto Uprising. In this case study, we showcase the use of drone multispectral imaging and handheld lidar scanning in conjunction with other geophysical techniques including electrical resistivity tomography, ground-penetrating radar, magnetic gradiometer, twin-probe resistance, and fixed-frequency electromagnetic surveying. The geophysical results were included in an interactive 3D site model to help identify a suitable site for excavation. To document the excavation and to validate and further interrogate the geophysical survey results, we used lidar-based photo-textured scans of the excavation that were incorporated into the 3D site model.
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