The Generalized Reciprocal Method — An Integrated Approach to Shallow Refraction Seismology

Abstract

The generalized reciprocal method (GRM) and two special cases, the conventional reciprocal method (CRM) and the intercept time method (ITM), constitute an integrated approach which is powerful and convenient for the great majority of exploration refraction problems. The ITM, the CRM and the GRM form a logical sequence of increasing depth of application, increasing performance and increasing complexity. They can be used as reconnaissance methods with widely spaced detectors or for detailed definition using closely spaced detectors. These methods are well suited to good quality control practices because the data, the processed data and the final depths can be readily presented. A most important benefit of these presentations, especially for geotechnical applications, is that they help resolve whether lateral changes in the seismic velocity associated with a major change in depth to a refractor, are in fact genuine, or simply an artefact of the interpretation algorithm. Two case histories illustrate the recognition of both fictitious changes in the seismic velocity associated with changes in the depth of the refractor, as well as genuine changes in the seismic velocity associated with a known fault.