Near surface S-wave velocity from upholes and surface seismic data

Saúl Ernesto Guevara, Gary F. Margrave

The near surface S-wave velocity model can be useful in overcoming the near-surface effect, an important issue in the processing of converted-wave (PS) or S-wave seismic data, ande can also contribute to other near surface problems.

An uphole survey, acquired in a location in a valley of the Colombian Andes is analysed here. An S-wave velocity model was obtained from these data, based on events that appear to be generated by the source (see the Figures below). The complex behaviour of this wavefield can give useful details about the S-wave field structure. These variations are not easily observable using conventional surface seismic data. Variations in the velocity model with depth were related to lithological characteristics. The uphole data were also compared to a 2D seismic line acquired at the same place, which gives clues about the characteristics of the horizontal component.

This is a first approach to the analysis of these data, which can provide useful clues about the near surface S-wave velocity model and the methods for its analysis.