Summary
Spatial resolution is associated with the temporal resolution, but mat be limited due to "diffraction" aperture or inaccurate velocities. Velocity errors occur when data are processed to a datum in violation of the hyperbolic assumption. These errors may be very small and are assumed to be negligible, especially with CMP processing. Prestack migrations gather data from many CMP gathers, and any relative velocity errors degrade the spatial resolution. We demonstrate this spatial resolution loss and recovery using a real 2D data set that contains faulting events. In addition, the resolution of the faults may be further focused, depending on their angle of obliquity to the 2D line.
Introduction
High spatial resolution data for a research project was acquired in the Hussar area of Alberta Canada. The sedimentary layers in the area are relatively horizontal, with a surface elevation that had a range of 100 m. A vertical component of the data was extracted and conventionally processes with a standard prestack migration. The results were typical of the area and displayed no faulting.
The data were also processed to form common scatterpoint (CSP) gathers, prestack migration gathers that are formed without moveout correction, (Bancroft et.al. 1994 and 1998). Velocity analysis of each gather provides a unique velocity at each CMP location. Moveout correction, scaling, muting, and stacking produced a prestack migration that appeared to contain faulted structure. The 2D data was further analyzed to evaluate the obliquity of the fault planes, relative to the angle of the 2D line, by modifying the velocities. These results showed improved focusing of the fault planes, identifying the angles of obliquity. It should be noted that vertical displacement across the faults is very small, but the character of the reflection changes significantly across the fault as demonstrated in Figure 1a. Note the character change between CMP 536 at 636 at 2 sec. near the bottom of the figure. This data was processed to a maximum time of 4.0 sec. Figure 1b shows the same area, processed with a poststack finite difference migration to a maximum time of 2.0 secs.