ABSTRACT
Geophysics can be dened several ways. In the broadest sense, geophysics is the application of physical principles to studies of the Earth (Sheriff, 2002). This general denition of geophysics encompasses a wide range of disciplines, such as hydrology, meteorology, physical oceanography, seismology, tectonophysics, etc. Geophysics, as it is used in this book, has a much more focused denition. Specically, geophysics is the application of physical quantity measurement techniques to provide information on conditions or features beneath the Earth’s surface. With the exception of borehole geophysical methods and soil probes like a cone penetrometer, these techniques are generally noninvasive, with physical quantities determined from measurements made mostly at or near the ground surface. (Note: Some large-scale airborne surveys are carried out with geophysical measurements collected by airplanes and helicopters positioned well above the surface, but these types of surveys are not within the scope of this book.) The geophysical methods employed to obtain subsurface information from surface-based measurements include resistivity, electromagnetic induction, ground-penetrating radar, magnetometry, self-potential, seismic, gravity, radio activity, nuclear magnetic resonance, induced polarization, etc.
