Post-stack diffraction-type migration of the signal component of the wavefield

Abstract

SUMMARY A new noise-suppressing technique for post-stack migration of CDP data is described. The idea of the method in its simplest form is to slide, in time, a diffraction curve along a group of traces of a stacked section, and for each point in time, to check whether there is an interval along the diffraction curve within which this curve is tangent to some coherent energy. If such an interval does exist, its location is found, a penalty function having maximal values within this interval and tending to zero outside it is constructed, and the data samples along the diffraction curve are stacked with weights proportional to the values of the penalty function. The method has been tested on variable fold seismic reflection data from a short seismic line at Cajon Pass in southern California. Results show substantial improvement in the ability to image a set of reflectors in the crystalline basement. The uppermost reflectors were intersected by the Cajon Pass scientific drillhole and found to be related to fracture zones. The source of a prominent reflector at 2.5 s (about 6.2 km depth), with an apparent dip of about 20° to the north, is not known. The northward dip of basement reflectors is common in seismic sections from the Mojave block where it abuts the San Andreas fault, and is probably related to a strong component of compression across the fault.