INTERPRETATION OF FIRST ARRIVAL TRAVEL-TIMES IN SEISMIC-REFRACTION WORK

The necessary condition for the seismic refraction method to succeed i s that the refracted first arrivals from each layer in a multilayered earth system should be detected on a seismogram as first arrivals, and this is possible only when velocities of all underlying layers are su ccessively greater. The usual procedure to interpret the refraction tr avel times is to fit such a data set with several intersecting straigh t lines by employing a visual technique which may lead to errors of su bjective judgment, as the velocity model depends on the selection of v arious line segments through the data. To remove the visual fit we pro pose here a layer stripping method based on minimum intercept time, ap parent velocity, rms residual, and maximum data points by least-square s fitting to yield several intersecting straight lines. Once data are segmented out, the conventional equations can be used to determine the velocity structure.