Chapter 5: Inversion for Applied Geophysics: A Tutorial
Throughout this book there are numerous cases where geophysics has been used to help solve practical environmental, geotechnical, and exploration problems. The typical scenario is first to identify the physical property that is diagnostic of the sought geologic structure or buried object, for example, density, seismic velocity, electrical conductivity, or magnetic susceptibility. The appropriate geophysical survey is then designed and field data are acquired and plotted. In some cases the information needed to solve the problem may be obtained directly from these plots, but in most cases more information about the subsurface is required. As an example, consider the magnetic field anomaly map presented in Figure 2. The existence of a buried object, and also approximate horizontal locations, can be inferred directly from that image. The map, however, presents no information about the depth of the object or details regarding its shape. To obtain that information the data need to be inverted to generate a 3D subsurface distribution of the magnetic material.
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).