Introduction

Refraction statics are often applied to data gathered in mountainous regions in order to correct the data to datum. The motivation for this is to enable standard processing techniques to be used on the data. Unfortunately, the refraction inversions often yield poor results which do not make sense geologically and which cause error in the statics corrections.

The refraction statics program considered here works by inverting the first break picks in order to obtain a model for the near surface low velocity layer. Once the near surface model is obtained, a static correction is calculated based on this model. The refraction inversion algorithm assumes that the first breaks are refracted head wave arrivals. In mountainous regions this assumption breaks down, and the presence of transmitted arrivals causes substantial error in the inversion. A ray tracing program is used to model refracted head wave and transmitted arrivals. These synthetic arrivals are input to the refraction inversion program to demonstrate that refraction statics programs fail when transmitted arrivals are present in the data. The transmitted arrivals are faster than the refracted head wave arrivals, and cause substantial error in the refraction statics inversion.