Using supervirtual first arrivals in controlled-source hardrock seismic imaging-well worth the effort

Abstract

Varied applications of seismic interferometry have arisen in the last decade; however, the potential of the method to improve reflection seismic processing in hardrock environments has not explicitly been regarded. Therefore, in this paper we investigate the potential of retrieving the first arrivals originally hindered by high noise level in the exploitation of controlledsource data acquired over the iron-oxide apatite-rich deposit at Grängesberg (Sweden) and its mining-induced structures. The supervirtual first arrivals retrieved using interferometry methodologies allowed first breaks to be picked more extensively than in the original data. Revised static corrections significantly improved the linearity of the first arrivals and continuity of reflections in the source gathers. Especially, reflections considerably enhanced in the source gathers stacked constructively in the final section. Comparison with geological data, supported by traveltime forward modelling, indicates that these reflections represent the unmined part of the deposit. Other reflections at shallower depth are interpreted as anthropogenic faults possibly located at lithological contacts. Tomographic inversion was also run using the augmented traveltime data. The greater resolution and penetration of this new tomographic image allowed better bridging with the results of the reflection seismic section. Velocity anomalies depict the presence of mining-induced structures and a potential 'Brewery fault', which is believed to put at risks an urban area. Even though the potential of first-arrival retrieval seems to be casedependent, this study illustrates that interferometry may substantially improve the accuracy of static corrections and subsequent stack for hardrock imaging, as well as in the penetration and resolution of traveltime tomograms.