Interpretation methods

Abstract

The idealized geological conditions and corresponding time—distance—depth relations in the examples given in Chapter 3 are seldom encountered in reality. The recorded raw travel time curves are generally distorted due to abrupt changes in topography and refractor configuration, variations in thickness and number of overburden layers and varying velocities in horizontal and vertical directions. The dry and loose near-surface layers constitute a special problem since their velocities generally are very low and, therefore, relatively small variations in thickness of the topmost layers influence the recorded arrival times to a higher degree than more prominent deep features where the velocity is higher.