NONINTERCHANGEABILITY OF SOURCES AND RECEIVERS IN A HETEROGENEOUS MEDIUM

Abstract

The starting point in the design of source patterns, seismometer groups, and multifolding parameters is a wave test. A wave test is usually performed with the source at a fixed location and the seismometers planted along a line at increasing distances from the source. If more coverage is desired than that provided by the length of the wave‐test cable, the cable is moved further from the source and source initiation is repeated. A wave test conducted with the source at a fixed location and the receivers planted at locations covering a range of distances from the source is here designated a normal wave test. Sometimes a wave‐test spread is kept fixed and the source is moved throughout a range of distances at intervals equal to the spread length to obtain the desired coverage. This may be termed a “semitransposed” wave test. It is sometimes desirable to perform a wave test in which a single receiver is kept at a fixed location and the source points are spaced at appropriately small intervals. This type of wave test is designated as a transposed wave test in this report. Principal interfering waves frequently can be identified by the use of a transposed wave test in certain areas where normal wave‐test sections indicate a confused mixture of waves having apparent velocities both toward and away from the source point. Comparison of transposed and normal wave‐test seismograms taken in such areas shows that source‐receiver interchangeability does not hold for the heterogeneous medium.