Chapter 30: “Poor Man’s 3D”—A Simple Approach to 3D Seismic Surveying: A Case History
Seismic surveys of near-surface structures are mostly restricted to 2D seismic sections. But the structures in this depth range (> 500 m) are often three dimensional, like in hydrocarbon exploration geophysics, where 3D seismic surveys are the norm today. If a three-dimensional structure is investigated with only a 2D section, misinterpretations may occur (e.g., resulting from laterally reflected waves or an unstable 2D migration) if the seismic line is not perpendicular to the geological strike direction. The general 3D seismic method is well developed today, but the costly field surveys and the costly data processing are the reasons that 3D seismic surveying is seldom used for nonexploration applications, e.g., for engineering and environmental or hydrogeologic questions. In this chapter, I want to recall a method earlier called “poor man’s 3D,” which may be a practicable alternative for near-surface geophysics that yields simple solutions for determining dip and strike of plane reflections in good data.
Figures & Tables
Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. Man interacts with this part of the earth’s crust: he walks on it; he drills and excavates into it; he constructs structures on and in it; he utilizes its water and mineral resources; and his wastes are stored on and in it and seep into it. 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 (see Chapter 2).