The Structural Significance of Seismic Velocity - A Progress Report
1981. "The Structural Significance of Seismic Velocity - A Progress Report", Pore Pressure: Fundamentals, General Ramifications, and Implications for Structural Geology (Revised), P. E. Gretener
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This is a further development of a paper given earlier at the SEG and AAPG meetings (Gretener,1977). Judging from the response the topic is timely and the additional treatment given here well deserved.
Geophysics is a geological tool. It is the most important tool of the modern geologist. Geophysical surveys enable us to determine the geometric distribution of certain physical properties in the subsurface. Generally this delineation conforms with the distribution of different rock types and, therefore, provides geological information. In the case of applied geophysics, directed towards the detection of hydrocarbons, groundwater, metallic ores, etc., the physical properties of the target itself or those of structures associated with it, must differ from those of the surroundings in order that detection is possible. One of the early and crucial choices in any geophysical survey is that of the nature of the physical property to be investigated. At that time it is also important to keep in mind that certain of these properties are related. As examples we may cite the frequent concurrence of low velocity and low density, or high velocity and high strength.
Amongst all the geophysical methods, seismic is the sharpest and most definitive tool when it comes to investigate the layered sequence of the sediments or that of the earth as a whole. The basic property under investigation is the change of seismic velocity from one layer to the next. It is thus possible to delineate from the surface the underground distribution of these changes. However, the