Feasibility of 3D Random Seismic Arrays for Subsurface Characterizations in Urban Environments

To test new and cost-effective methods for 3D subsurface characterization in urban and near-surface environments, along with mapping bedrock morphology and zones of weaknesses at a contaminated site, a seismic survey was conducted in the city of Varberg, southern Sweden. The survey consisted of 12 active-source landstreamer seismic profiles, 89 randomly distributed wireless seismic recorders along an area of 350x300 m and 46 wireless recorders deployed along the train tacks crossing the site. In this study, we analyzed the properties and potential of two datasets obtained only from the wireless recorders for seismic imaging. One dataset consists of recordings of shots done along the active-source profiles, while the other one consists of 5 days of passive seismic data recording. The first dataset was used for first-break traveltime tomography with the picked data indicating uniform source-receiver azimuth-offset distribution and minor acquisition footprints. P-wave velocity model obtained from the inversion was successful in imaging bedrock surface and indicated two preferential directions from which contaminants may migrate away from the main contaminated site. Preliminary analysis indicates that the site’s noisy nature limits 3D reflection seismic potential of the dataset with active source recordings while the passive dataset shows promising results for site characterization.