Automatic identification of multiply diffracted waves and their ordered scattering paths

Abstract

An automated algorithm uses recordings of acoustic energy across a spatially-distributed array to derive information about multiply scattered acoustic waves in heterogeneous media. The arrival time and scattering-order of each recorded diffracted acoustic wave, and the exact sequence of diffractors encountered by that wave, are estimated without requiring an explicit model of the medium through which the wave propagated. Individual diffractors are identified on the basis of their unique single-scattering relative travel-time curves (move-outs) across the array, and secondary (twice-scattered) waves are detected using semblance analysis along temporally offset primary move-outs. This information is sufficient to estimate travel times and scattering paths of all multiply diffracted waves of any order, and for these events to be identified in recorded data. The algorithm is applied to synthetic acoustic data sets from a variety of media, including different numbers of point-diffractors and a medium with strong heterogeneity and non-hyperbolic move-outs.

Imaging vertical interfaces using acoustic time reversal

“…For these reasons we might boost the amplitudes at later times in the recorded data prior to imaging to help to increase the magnitude of the contributions from the duplex waves, noting that inevitably gaining the amplitudes at later times can introduce or increase noise in the recorded data. As an alternative, and Löer et al (2015) developed algorithms that in principle are capable of identifying specific orders of diffracted wavefields, and a related method for reflected waves was developed by da Costa Filho et al (2017). Hence, it may be possible in future to identify the multiply scattered waves that correspond to each primary in seismic data, and increase the amplitudes of these waves without boosting the surrounding noise.…”

An introduction to seismic diffraction

“…To better appreciate the implications of these systematic observations in the autocorrelation, a conceptual sketch of the considered multiple scattering process (for two and four diffractors) and its controlled-source analog is displayed in Figure 33. As was recently suggested by other authors, the fact that the moveout connected to a point diffraction is always the same can be used to systematically investigate the order in which observed scattering occurred (Dylan Mikesell et al, 2012;Meles and Curtis, 2014;Löer et al, 2015). Here, I seek to demonstrate that with the help of wavefield separation and tagging, under certain conditions, inter-scatterer traveltimes can be extracted interferometrically from the coda by means of simple auto-correlation.…”

Relating source-receiver interferometry to an inverse-scattering series to derive a new method to estimate internal multiples

“…The latter of the three methods, SRI, has been subject to increasing interest due to its close relationship to seismic imaging methods and the new perspective it provides on nonlinear imaging schemes and so-called extended images (Vasconcelos et al, 2010;Fleury and Vasconcelos, 2012;Ravasi and Curtis, 2013;Ravasi et al, 2014). Other applications of SRI include ground-roll removal in land-based exploration seismology (Duguid et al, 2011), construction of underside reflections from borehole recordings (Poliannikov, 2011), retrospectively observing seismograms from old earthquakes in seismology Entwistle et al, 2015), suppression of nonphysical reflections in standard interferometry (King and Curtis, 2012), and prediction of multiply diffracted events and identification of scattering paths Löer et al, 2015). We focus on this last application and show that by considering multiple reflected scattering paths, a new method is obtained to predict internal multiples in reflection seismic data.…”