Seismic methods

The most challenging of these applications has been the location and characterisation of anomalies in thick concrete structures using seismic methods and the detection of reinforcing steel and pre-stressing cables in congested structures using radar. 

The commercial value of a clay deposit depends on market trends, competitive materials, transportation faciflties, new machinery and processes, and labor and fuel costs. Naturally exposed outcrops, geological area and stmcture maps, aerial photographs, hand and power auger drills, core drills, earth resistivity, and shallow seismic methods are used ia exploration for clays (32). Clays are mined primarily by open-pit operation, including hydraulic extraction however, underground mining is also practiced. 

Exploration for Natural Gas and Oil by Seismic Method (Geophysical Prospecting). It is... 

Geophone. An extremely sensitive electromechanical device used as recording instrument iri seismic prospecting. See in this Vol, under "Exploration for Natural Gas and Oil by Seismic Method , p E358-L to E359-L... 

Exploration for natural gas and oil by seismic method 6 E358—E359... 

Seismic methods are often used to map depth to specific horizons such as bedrock, clay layers and water table. 

Figure 12 shows a schematic view of sound waves traveling through a two layered system of soil over bedrock. A seismic source produces sound waves which travel in all directions into the ground. The seismic method is only concerned with the wave paths shown in Figure 12. One of these waves, the direct wave, travels parallel to the ground s surface in the surface layer.

Note in conclusion that due to the high resolution of the seismic method, it is one of the leading geophysical methods, especially in oil and gas prospecting. 

Thus while the inverse operator (15.98) determines the distribution of the anomalous square slowness within the medium, formula (15.99) solves for the reflectors and the corresponding reflection coefficients. In geophysical applications, for example in seismic methods, the reflecting boundaries are the main target of exploration. That is why inversion formula (15.99) plays an important role in the interpretation of seismic data. In the next section we will show that this method can be extended to a 3-D case. This technique provides the basis for modern methods of seismic data interpretation. 

Emphasis has also been placed on the fundamental principles of surface seepage, and the interpretation of the data. It is the opinion of the authors that the overall acceptance of microseep technology in the West has been hindered not only by the emphasis and success of seismic methods but also because of the lack of a comprehensive and public surface geochemistry database. There are, by comparison, more publications on geochemical survey data and basic concepts in the Soviet and Russian literature. As a consequence, many of our discussions rely on experience gained in the private sector in the West, supplemented by literature published in the East. 

To a geologist who has not worked with seismic data, this situation is confusing. Even among seismologists, there is disagreement as to what features of the different models are genuine characteristics of the velocity structures beneath shields. For this reason, we thought it would be helpful to discuss what features can and cannot be well resolved by the various seismic methods as well as the seismic data that have been used. However, it was unexpectedly difficult in some cases to make accurate comparisons of the various models because they use different radial... 

Seismic, heat-flow and xenolith data provide constraints on different physical properties, and differences between estimates are expected. Seismic methods determine the depth to a low-velocity zone at the base of higher-velocity lithospheric lid (e.g. James Pouch 2002 Ken-... 

Of much greater importance with regard to the unravelling of trapping configurations was the development of seismic methods. The first seismic profile was actually already recorded by O. Hecker in 19(K) but it took some time to achieve practically useful results. 

The reflection seismic method, that would eventually supplant the refraction technique, was patented in 1914 by R. Fessenden in the USA. Use of this method for oil exploration was proposed by J.C. Kar-cher in 1917. In 1921 the first field tests were carried out in the USA, but it took until 1929 before the first successes were achieved (Forbes and O Beime, 1957). Soon afterwards the method was already used in several countries often together with the refraction technique. A good example of an early reflection seismogram that resulted in the discovery of a field is shown in Fig. 8. The Tucupita field in eastern Venezuela was discovered on the basis of seismic surveys carried out in the period 1939-1941 (LeRoy, 1951). 

After 1955, there was an avalanche of papers on trapping and the subject gradually reached a status that one can speak of as true quantification, with the possibility of making reliable predictions. Undoubtedly, the development of seismic methods made a very large impact in the delineation of trapping configurations. However, also outcrop observations and laboratory experiments contributed markedly to the... 

The principal observation behind the Helffrich and Wood (2001) model of the mantle is that the scattering of seismic waves in the lower mantle indicates that small heterogeneities are present, mostly about 4 km in size. As with all seismic methods the physical cause of the seismic scattering anomalies could theoretically be either thermal or compositional in origin. Helffrich and Wood (2001)... 

Soon after the geophysical prospecting, the roadway of coal seam 8 ran through the geological abnormal part determined by the three-dimensional seismic method. The roadway materials showed that the 1 geological abnormal objective is a collapse column and contains no waters, which is consistent with the explanation of prospecting outcome. 

Seismic Reflection seismic methods can be used to create images of the geologic changes and some of the above discussed anomalies. 2D and 3D seismic surveys are highly effective subsurface analytical tools for potash exploration used in the identification and estimation of the degree of salt loss, salt dissolution-induced collapse structures, and the identification of other geological elements. These seismic programs can help complete a picture of the subsurface that should enhance the ability of the exploration team to successfully select well locations. 

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