The method of refracted waves (MPE, seismic refraction, refraction shooting technique) is a seismic exploration method using elastic waves generated by the movement of the front of a sliding wave along the refracting boundary - the roof of a high-speed layer [1] . The second most important seismic survey method [2] .
Theory
A sliding wave is formed by the incidence of a seismic wave on a refracting boundary at a critical angle, which in optics is called the angle of total internal reflection . The critical angle value is calculated using Snell's law.
where i is the critical angle, V 1 is the speed of the seismic wave above the border, V 2 is the speed of the seismic wave under the border.
The hodograph of the refracted wave has the shape of a straight line, with a starting point, with coordinates:
where i is the critical angle, h 1 is the thickness of the layer above the boundary, l b is the distance (distance between the source and receiver) of the starting point, t b is the time the refracted wave entered the starting point
Usage
The method of refracted waves is used in exploration geophysics when mapping the level of groundwater , the surface of the crystalline basement of ancient platforms [4] and the Mohorovichich border (“M”) [5] , the roof of rocky soils under the thickness of dispersed ones, identifying decompression zones [6] .
Modifications
Traditionally, MPV uses refracted waves that were the first to arrive at the geophone , that is, “in the first arrivals” [7] . In the correlation method of refracted waves (CMPW) [8] , created by Gamburtsev , subsequent arrivals are also used, sections of seismograms where refracted waves are not the first to be observed.
Method History
The method was first patented by Ludger Mintrop in 1919 (German patent No. 371963, "Method for determining geological structures") [9] . In fact, the document was issued 7 years later, in 1926. For some time, the refracted waves were called "Mintropovskie" [10] . Later, in the second half of the 20th century, they began to use the term “head waves” instead of the term “Mintropovskie” [11] . However, the Ministry of Transport itself in the patent did not cite the theory of the formation of refracted waves [12] , which was done in 1926 by the Soviet geophysicist Alexander Ignatievich Zaborovsky in the article “On the theory of traveltime curves ” [13] .
Weaknesses
According to the Zöppritz equations, the amplitude of a gliding wave, whose movement according to the Huygens-Fresnel principle generates refracted waves, must be equal to zero, which makes its existence theoretically impossible.
Velocities determined from the MPV data may contain relative errors of up to 50% [14] .
Notes
- ↑ VSEGEI . www.vsegei.ru. Date of appeal April 18, 2018.
- ↑ Moscow State University named after M.V. Lomonosov. A series of biology, soil science, geology, geography . - 1956. - 448 p.
- ↑ Technical Encyclopedia . - Directmedia, 2013-03-15. - 458 p. - ISBN 9785445805656 .
- ↑ Organization and management of the oil industry . - 1969. - 1026 p.
- ↑ Roman Aizberg, Tatyana Starchik. Synrift geodynamics of the Pripyat trough . - Litres, 2017-09-05. - 150 s. - ISBN 9785457630376 .
- ↑ Selyukov E.I. Brief essays on practical microgeodynamics . - Publishing House "Peter", 2010-03-11. - 176 p. - ISBN 9785498076423 .
- ↑ Tatyana Dmitrievna Ilyina, Institute of the History of Natural Science and Technology (USSR Academy of Sciences). Formation of the Soviet school of exploratory geophysics, 1917-1941 - Science, 1983 .-- 222 p.
- ↑ A. Vartanov. Physical and technical control and monitoring during the development of the underground space of cities . - Litres, 2017-09-26. - 548 p. - ISBN 9785040816439 .
- ↑ George Elliott Sweet. The history of geophysical prospecting . - Neville Spearman, 1978.- 440 p.
- ↑ Tatyana Dmitrievna Ilyina, Institute of the History of Natural Science and Technology (USSR Academy of Sciences). Formation of the Soviet school of exploratory geophysics, 1917-1941 - Science, 1983 .-- 222 p.
- ↑ Antonina Mikhailovna Yepinatieva. The method of refracted waves . - Nedra, 1990 .-- 312 p.
- ↑ Moscow State University named after MV Lomonosov Section of the History and Methodology of Natural Science. History and methodology of natural sciences . - Publishing house of Moscow University, 1987. - 196 p.
- ↑ Moscow University Physics Bulletin: Geology . - Moscow University., 1994. - 608 p.
- ↑ A.K. Urupov. The study of speeds in seismic exploration . - Ripol Classic, 2013-02. - 225 p. - ISBN 9785458533362 .