International Geologiical Congress - Oslo 2008

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EIE-07 High-resolution geophysical imaging of geological structures and processes in environmental studies

 

Opportunities and limitation of minimal invasive and tomographic methods for near surface investigation

 

Peter Dietrich, Hemholtz Centre for Environmental Research (Germany)
 

 

Nowadays there is an increasing need to observe and investigate natural and anthropogenic-influenced systems. Challenges for monitoring- and exploration technologies in environmental research are among others the identification and parameterization of system relevant physical-chemical-biological processes as well as the interaction between different scales. These challenges require high resolution methods.
In particular, cost-effective methods of minimal destructive nature and rapid application are taken into consideration. Methods for near surface investigation are direct-push (DP) technologies, borehole based as well as tomographic methods. Classical borehole based methods as well logging and sampling can deliver a high vertical resolution. But beside their high cost related to the drilling efforts, they suffer from a lack of information in lateral direction, i.e. between the boreholes. Other borehole based method as tracer and pumping tests can give information on the space between the boreholes, but the spatial resolution is very low.
Another option to get vertical profile information with high resolution is the use of DP technologies. These technologies can be used for a cost-effective characterization of the subsurface in terms of (geological) structure, distribution of contaminants as well as for the installation of sampling and monitoring equipment. The applicability of these technologies strongly depends on the geotechnical / mechanical characteristics of the subsurface material. Also if the application of DP technology allows for the same cost the measurement of much more profiles as compared to boreholes, it still suffers from the lack of spatial coverage in lateral directions. An alternative approach to compensate the poor lateral resolution is the application of tomographic methods (i.e. p- and s-waves seismic, DC-geoelectric, radar and hydraulic) using boreholes and/or DP. They deliver spatial continuous information and have a better resolution in deeper parts of the investigated area as only surface based measurements. But it should be taken into account that the spatial and parameter resolution strongly depends on the configuration of tomographic surveys.

 

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