Interpreting Colin Zelt's “Shootout” Seismic Refraction Data Set Using the Generalized Reciprocal Method

2012 ◽  
Author(s):  
Charles Stoyer
Keyword(s):  
Seismic Refraction ◽  
Data Set ◽  
Seismic Refraction Data ◽  
Reciprocal Method ◽  
Refraction Data

An Introduction to the generalized reciprocal method of seismic refraction interpretation

Geophysics ◽  
1981 ◽  
Vol 46 (11) ◽  
pp. 1508-1518 ◽  
Author(s):  
Derecke Palmer
Keyword(s):  
Average Velocity ◽  
Seismic Refraction ◽  
Velocity Analysis ◽  
Velocity Gradients ◽  
Variable Distance ◽  
Velocity Changes ◽  
Seismic Refraction Data ◽  
Reciprocal Method ◽  
Refraction Data ◽  
Overlying Strata

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.

scholarly journals Analisis Data Seismik Refraksi dengan Metode Generalized-Reciprocal

2012 ◽  
Vol 3 (1) ◽  
pp. 162
Author(s):  
Ashadi Salim
Keyword(s):  
Wave Velocity ◽  
Seismic Wave ◽  
Approximate Calculation ◽  
Seismic Refraction ◽  
Velocity Analysis ◽  
Seismic Wave Velocity ◽  
Seismic Refraction Data ◽  
Reciprocal Method ◽  
Refraction Data

The analysis of seismic refraction data by the generalized reciprocal method can be used for delineating undulating refractors. The forward and reverse times of arrival at different geophones with XY distance along a refraction profile, are used for calculating time depth. The seismic wave velocity in refractor may be obtained from velocity analysis function, and the depth of refractor under each geophone is obtained from time-depths function. This method has been applied at one line of seismic refraction measurement that was 440 m long with 45 geophone positions. The measurement obtained 20 m as the optimum XY-value and 2250 m/s as the velocity of seismic wave in refractor, and the undulating refractor topography with the depths varies 10.4 – 22.1 m. The optimum XY-value was obtained from approximate calculation derived from the observation, that was indicated the absent of undetected layer.

Obtaining multilayer reciprocal times through phantoming

Geophysics ◽  
1986 ◽  
Vol 51 (1) ◽  
pp. 45-49 ◽  
Author(s):  
Robert W. Lankston ◽  
Marian M. Lankston
Keyword(s):  
Critical Parameter ◽  
Seismic Refraction ◽  
Special Equipment ◽  
Seismic Line ◽  
Arrival Times ◽  
Seismic Refraction Data ◽  
Reciprocal Method ◽  
Refraction Data

A critical parameter in interpreting seismic refraction data with the generalized reciprocal method (GRM) is the reciprocal time, which must be available for each layer from which refracted rays return to the surface. The reciprocal time can be measured in the field, but this requires special equipment or procedures. Shooting to obtain the reciprocal time from each layer along a long seismic line may be operationally impractical. However, the method of phantoming arrivals overcame the problems. In phantoming, a reciprocal time is actually measured along any length of the seismic refraction line for any refractor and that value can be used as the reciprocal time in GRM processing if the first‐break arrival times are phantomed properly. Realizing that the reciprocal time may be extracted from overlapping normal forward and reverse shots and phantoming the data accordingly will save much field time and expense. An example shows the results of using a reciprocal time measured across one spread for simultaneously processing and interpreting collinear, overlapping spreads.

scholarly journals Inversion of seismic refraction data using genetic algorithms

Geophysics ◽  
1996 ◽  
Vol 61 (6) ◽  
pp. 1715-1727 ◽  
Author(s):  
Fabio Boschetti ◽  
Mike C. Dentith ◽  
Ron D. List
Keyword(s):  
Genetic Algorithm ◽  
Genetic Algorithms ◽  
Seismic Refraction ◽  
Solution Space ◽  
Optimization Methods ◽  
Data Set ◽  
Weathered Layer ◽  
Seismic Refraction Data ◽  
Refraction Data

The use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the nonlinearity inherent in such applications. However, in their application to specific problems, as with all algorithms, problems of implementation arise. After extensive numerical tests, we implemented a genetic algorithm to efficiently invert several sets of synthetic seismic refraction data. In particular, we aimed at overcoming one of the main problems in the application of genetic algorithms to geophysical problems: i.e., high dimensionality. The addition of a pseudo‐subspace method to the genetic algorithm, whereby the complexity and dimensionality of a problem is progressively increased during the inversion, improves the convergence of the process. The method allows the region of the solution space containing the global minimum to be quickly found. The use of local optimization methods at the last stage of the search further improves the quality of the inversion. The genetic algorithm has been tested on a field data set to determine the structure and base of the weathered layer (regolith) overlaying a basement of granite and greenstones in an Archaean terrain of Western Australia.

Controls of traveltime data and problems of the generalized reciprocal method

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1626-1632 ◽  
Author(s):  
Tak Ming Leung
Keyword(s):  
Seismic Refraction ◽  
Seismic Model ◽  
Inversion Process ◽  
Offset Distance ◽  
Ray Trace ◽  
Seismic Refraction Data ◽  
High Degree ◽  
Process Controls ◽  
Reciprocal Method ◽  
Refraction Data

Traveltime data required for 2D seismic refraction surveys are 2D first arrivals. To obtain a high degree of consistency between traveltime data and the seismic model, it is important to verify that traveltime data are appropriate for interpretation or an inversion process. Controls or checkpoints presented here inspect compatibility among traveltime data. Similar to the ray‐trace check on the consistency of interpretation, these controls provide an objective means of quality assessment of seismic refraction data. The theoretical aspects of the generalized reciprocal method (GRM) are studied because concerns have been raised regarding the accuracy of some interpretations using this method. The problem of the GRM is that the optimum XY value, which is the most important parameter in the method, is assumed to be twice the offset distance. Consequently, based on this unproven assumption, the efficacy of the optimum XY value is somewhat exaggerated.

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