Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. The very outermost part of the Earth’s crust is extremely dynamic—in both technical (physical properties) and nontechnical (political, social, legal) terms—which leads to both technical and nontechnical challenges that are much different than the challenges faced by “traditional” applications of geophysics for regional geologic mapping and for oil and gas exploration.
Near-surface geophysics investigations include numerous and varied application areas and both basic and applied research in support of those applications (National Research Council, 2000). These application areas are characterized by various descriptors, e.g., engineering, geotechnical, environmental, groundwater, mining, archaeological, forensic.
Some typical examples of these application areas are:
• Engineering and geotechnical geophysics: characterization of the foundation beneath critical structures; mapping top of rock; nondestructive evaluation of engineered structures, e.g., bridges, buildings, dams, etc.; cavity and tunnel detection; geologic mapping.
• Environmental geophysics: mapping contaminant plumes in groundwater; locating buried cultural features, e.g., metal containers, unexploded ordnance (UXO), landfills, underground storage tanks; monitoring changes in the hydrogeological regime; geologic mapping.
• Groundwater geophysics: locating optimal water-well drilling sites; mapping the water table; locating fracture zones; groundwater quality assessment; defining geology (stratigraphy, structure, aquifers, and aquicludes, etc.) for input to groundwater modeling efforts.
• Mining geophysics: mapping geologic structure; locating and characterizing ore deposits; ore quantity and quality estimates.
• Archaeological geophysics: locating and assessing archaeological sites; cultural resource management; locating historic and prehistoric graves, hearths, burial pits, etc.; mapping building foundations; locating artifacts.
• Forensic geophysics: clandestine burials; crime scene investigation; drug and weapons caches; intrusion tunnels.
The near-surface geophysics application areas listed above are characterized and distinguished by
• shallow depths of investigation or interest
• requirements for high resolution, vertically and horizontally
• the possibility of near-real-time confirmation, verification, or validation of the results
• program planning, field and laboratory execution, and results interpretation and presentation that are subject to public health and safety concerns and constrained by legal and regulatory considerations