The Value of Borehole -to-surface Information in Near-surface Crosswell Seismic Tomography

Detailed information about the spatial distribution of subsurface properties is important in many fields. One method that can image the seismic velocity structure of the shallow subsurface is crosswell seismic tomography. By including rays traveling from the boreholes to the surface, the angular coverage of crosswell tomograms can be significantly improved. We investigated the effects of these borehole-to-surface rays on synthetic and field data. The tests on synthetic data showed that including borehole-tosurface information did not significantly change the tomogram’s resolution. Tomographic inversion of a field data set collected at the Boise Hydrogeophysical Research Site, however, showed that including borehole-to-surface information improves a tomogram’s ability to image layer boundaries, and improves the velocity estimates for slow layers. The tomogram generated using the crosswell and borehole-to-surface information is consistent with the previously interpreted hydrostratigraphic units at the site.