Repeatability in geophysical data processing: A case study of seismic refraction tomography

摘要

This research work was carried out to determine the extent to which a geophysical data could give similar results (anomalies) when reprocessed under the same condition. Hence seismic refraction tomography processing which depends on picked arrival times was carried out to ascertain this fact. The processing flow started from importing raw seismic data, down to generation of the tomography model that represent the distribution of seismic velocities within the subsurface. Each of the two different raw seismic data collected from two profiles was reprocessed for three times, under the same condition, using the same software. The major factor that naturally varied during the data processing was the picked first arrival travel times. The results showed similar velocity distribution within the subsurface in each of the three models, that is, areas of low velocities corresponding with areas of low velocities and vies versa. The average thickness of the overburden and depth to basement appeared to be the same in all the tomographic models. However, subtle features like the subsurface geometry and basement topography did not show much similarity in appearance. It was concluded that geophysical data should be processed at least three times along with other constrain, and the extent of repeatability observed, before any meaningful interpretation can be drawn from it. This has also revealed that in the event of time laps investigation, geophysical data should be reprocessed several times to ensure that the observed changes are not due to processing artefact, rather that geological changes.