Abstract

Seismic imaging of the shallow subsurface (approximately 5 m) can be very challenging when reflections are absent and the data are dominated by ground roll. I analyzed the transmission coda to produce fine-scale, interpretable vertical and horizontal component seismic velocity (VP and VSH) models using full-waveform inversion (FWI). Application of FWI is tested through imaging two buried targets. The first target is a pair of well-documented utility pipes with known diameters (0.8 m) and burial depths (approximately 1.5 m). The second target is a poorly documented former location of the pipe(s), which is now a backfilled void. Data are acquired along a 23 m 2D profile using a static array with single-component vertical and horizontal geophones. Our results indicate considerable velocity updates in the VP and VSH models across the pipes and backfill. The pipes appear as negative velocity updates in the final inverted VP and VSH models, whereas the backfilled area represents negative and positive velocity updates in the VP and VSH models, respectively. Variations of the polarities in the inverted models (VP and VSH) across the backfill can be indicative of the medium, which respond differently to the vertical and horizontal component seismic waves. The attenuation models show a general decreasing trend with increasing depth. Therefore, simultaneous applications of vertical (VP) and horizontal (VSH) component seismic velocity modeling can be an effective tool to understand the subsurface medium in near-surface characterization.

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