Plus minus method
The plus minus method is a geophysical principle attributed to J. G. Hagedoorn for statics solution derivation in which two emergence points on a refractor and a common midpoint (cmp) on the surface are considered. It is used to interpret seismic refraction profiles over irregular layers whose slope angles are less than 10°. Both forward and reverse shooting allow for matched time-distance graphs to be plotted.
The 'Plus' component of the method allows for the perpendicular depth to the refractor to be calculated. The 'Minus' component helps determine the seismic velocity of the refractive medium.
Examples:
t+ = tABCD + tDEFG - tABFG
t- = tABCD - tDEFG + tABFG
see the figure in the Seismic Data Processing text by Ozdogan Yilmaz on pg 227
References
Further reading
- "The Plus-Minus Method of Interpreting Seismic Refraction Sections" authored by J.G. Hagedoorn presented to the fifteenth meeting of the European Association of Exploration Geophysicists in London from 10 to 12 December 1958. Published in Geophysical Prospecting, the Plus-minus method is elaborated on pg. 67
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