Super-virtual refraction interferometry: Theory


Inverting for the subsurface velocity distribution by refraction traveltime tomography is a well accepted imaging method by both the exploration and earthquake seismology communities. A significant drawback, however, is that the recorded traces become noisier with increasing offset from the source position, and so prevents accurate picking of traveltimes in far offset traces. To enhance the signal to noise ratio of the far offset traces, we present the theory of super virtual refraction interferometry where the signal to noise ratio (SNR) of far offset head wave arrivals can be theoretically increased by a factor proportional to N; here, N is the number of receiver and source positions associated with the recording and generation of the head wave arrival. There are two steps to this methodology: correlation and summation of the data to generate traces with virtual head wave arrivals, followed by the convolution of the data with the virtual traces to create traces with super virtual head wave arrivals. This method is valid for any medium that generates head wave arrivals. There are at least three significant benefits to this methodology: 1). enhanced SNR of far offset traces so the first arrival traveltimes of the noisy far offset traces can be more reliably picked to extend the useful aperture of data, 2). the SNR of head waves in a trace that arrive after the first arrival can be enhanced for accurate traveltime picking and subsequent inversion by traveltime tomography, and 3). common receiver pair gathers can be analyzed to detect the presence of diving waves in the first arrivals, which can be used to assess the nature of the refracting boundary.

SEG Technical Program Expanded Abstracts 2011