An Introduction to the generalized reciprocal method of seismic refraction interpretation

Abstract

The generalized reciprocal method (GRM) is a technique for delineating undulating refractors at any depth from in‐line seismic refraction data consisting of forward and reverse traveltimes. The traveltimes at two geophones, separated by a variable distance XY, are used in refractor velocity analysis and time‐depth calculations. At the optimum XY spacing, the upward traveling segments of the rays to each geophone emerge from near the same point on the refractor. This results in the refractor velocity analysis being the simplest and the time‐depths showing the most detail. In contrast, the conventional reciprocal method which has XY equal to zero is especially prone to produce numerous fictitious refractor velocity changes, as well as producing gross smoothing of irregular refractor topography. The depth conversion factor is relatively insensitive to dip angles up to about 20 degrees, because both forward and reverse data are used. As a result, depth calculations to an undulating refractor are particularly convenient even when the overlying strata have velocity gradients. The GRM provides a means of recognizing and accommodating undetected layers, provided an optimum XY value can be recovered from the traveltime data, the refractor velocity analysis, and/or the time‐depths. The presence of undetected layers can be inferred when the observed optimum XY value differs from the XY value calculated from the computed depth section. The undetected layers can be accommodated by using an average velocity based on the optimum XY value. This average velocity permits accurate depth calculations with commonly encountered velocity contrasts.

Statistical analysis of data processing in some seismic refraction methods: A synthetic data example

“…Since the concepts are well known, the mathematical framework of the methods are briefly illustrated and explained. The generalized reciprocal method (GRM) (Palmer, 1981) is not considered here due to query by several authors in practically estimating the so called optimum migration distance (Sjögren, 2000;Leung, 1995;Whiteley, 1990).…”

Automatic detection of ovarian cancer based on improved DWT transformation

“…Low cost, simple application and diverse interpretation methods have raised the application of this method in the study of sites and other engineered structures [7,8]. In this method, measurements are carried out by creation of seismic wave by artificial energy sources (explosion or mechanical) in one point and determination of the arrival time of direct, reflected and refracted waves to the layers interface equipped with a series of receptors located in a direct line on the land surface ( Figure 1).…”

Earthquake Mitigation in the Lisbon and Lower Tagus Valley area, Portugal

“…Palmer, 1981). Using this methodology we are able to derive an appropriate relation between seismic velocities and geological formation, lithology, age and depth of burial.…”