Seismic refraction survey in imperial valley geovision typically uses the oyo das1 or geometrics r2460 seismograph for refraction and reflection investigations. Basic principles of the seismic method tu delft ocw. Seismic methods can provide valuable information of the subsurface, such as the seismic velocity structure of the geology e. One of the founders of the seismic refraction method was german scientist ludger mintrop. Introduction to seismic method linkedin slideshare. Difference between cell wall and cell membrane december 19, 2009. Refraction and reflection seismics serve different purposes. A seismic refraction or seismic reflection line is a set of seismographs usually lined up along the earths surface to record seismic waves generated by an explosion for the purpose of recording reflections and refractions of these waves from velocity discontinuities within the earth. Although, active seismic methods have been very successfully used in exploration for oil and the theory and field procedures are well established, their use in geothermal exploration has been rather limited. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time.
In the earth, seismic waves can propagate as longitudinal p or as shear s waves. Seismic refraction is a geophysical principle see refraction governed by snells law. Well log analysis exhibited possible sand zones at about 30m, 50m, 75m, and 122m. Penobscot bay, is here interpreted on the basis of both refracted and reflected phases. The refraction seismic method is normally used for localized nearsurface investigations site surveys. Masw versus refraction seismic method in terms of acquisition and processing of data and the accuracy of estimation of velocity profiles. Knowing the difference between reflection and refraction will help you understand basic phenomenon of science. Furthermore is shown in chapter v, how the results of these two independent methods are used to get reliable information about the investigated area. Reflection and refraction seismic methods springerlink. A comparative analysis of various seismic refraction.
Use of surface reflection refraction methods to characterize the near surface, generally the upper 100 m, is a much younger application, but is still based on about two decades of. Let see from this picture, refraction method start by sources of waves, when it travels through earth, wave will refracted and follow the nearest layer from ground. Seismic resolution is controlled by the bandwidth of the signal, which is typically f30140 hz. Refraction and reflection seismology physics stack exchange. Conventional raytracing analysis of refracted and wideangle reflected phases in the refraction data constrains the velocity structure to about 14 km depth, and provides evidence for highveiocity material 6. Processing was done using mainly open source software seismic unix. According to the strengths and weaknesses comparison of the two methods we conclude that masw or reflection can be selected as a method of choice depending on the required information, either continuous v s profiles or structural images. The seismic refraction method is based on the measurement of the travel time of seismic waves refracted at the interfaces between subsurface layers of different velocity. When a seismic wave travelling through the earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. One of the most important differences between the maps in figs. Jul 19, 2017 for both marine seismic reflection and refraction methods, the primary principles are based around the notion of sending artificiallygenerated sound waves downward into the earth and recording the energy that returns to recording instruments receivers. Ppt seismic refraction powerpoint presentation free to. A comparison between masw and reflection methods based on the results of this study is summarized in table 2. Aayush kesarwani, aditi sharma, chirag jain, indian school of mines summary near surface geophysical surveys commonly involve determination of seismic velocities and hence subsoil characterization.
Seismic method including single channel seismic and multichannel seismic method is one of the most effective methods for the identification and prediction of submarine gas hydrate. Refraction, interpretation, seismic, reciprocal method, delay time, tomography introduction seismic refraction is considered to be paramount in engineering geophysics. Ye yincan et al, in marine geohazards in china, 2017. Definition of seismic reflection method in this geophysical prospecting technique, the structure of subsurface formations is mapped by making use of the times required for a seismic wave or pulse, generated in the earth by a nearsurface explosion of dynamite or by other artificial sources, to return to the surface after reflection from the.
Masw versus refraction seismic method in terms of acquisition. Seismic energy is provided by a source shot located on the surface. What is the difference between seismic reflection and refraction. Reflection seismic observations can be more readily interpreted in terms of complex geology. Within 10 years, the dominant method of hydrocarbon exploration. Seismic reflection surveys have been used successfully in petroleum and geothermal exploration projects and to investigate for shallow coal. Lecture 2 seismic refraction methods seismology refraction. Techniques used in seismic reflection processing, including normal. Common areas of dense seismic reflections were found between 75m and 300m across pure shear and converted wave images. Seismic methods are the most commonly conducted geophysical surveys for engineering investigations. These methods include seismic reflection and refraction surveys, and travel time residual and attenuation studies. On the flip side, refraction is when light is absorbed by the medium but the direction and speed is affected.
In principle, seismic data acquisition requires an energy source, a receiver, and a recording system. Measurement of seismicwave travel time is one of the most common geophysical method. Seismic reflection and refraction are frequently practiced methods for mapping subsurface structure in sedimentary formation in connection with coal, oil, and gas exploration. Seismic refraction provides engineers and geologists with the most basic of geologic data via simple procedures with common equipment.
Seismic reflection and refraction are frequently practiced methods for mapping subsurface. Seismic exploration is divided into refraction and reflection surveys, depending on whether the predominant portion of the seismic waves travel is ho. Reflection, is when the light goes back to the previous medium, but changes direction. Basic principles of the seismic method tu delft opencourseware. Reflection frequencies decrease with depth because of attenuation of seismic waves, and this also decreases the resolution at depth. Reflection and refraction seismology are both ways to study the structure of the earth near the surface. Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, seismic refraction traverses seismic lines are performed using a seismographs and or geophones, in an array and an energy source. Seismic refraction surveying universiti kebangsaan malaysia. Here we present the results of seismic refraction and reflection studies. A reflection gives out a perfect or almost perfect representation of an object. The main differences in velocitydepth data between the two methods are that the downhole data tend to expose a slightly greater number of distinct velocity layers. Basic principles of the seismic method in this chapter we introduce the basic notion of seismic waves.
The reflection seismic method is typically used to investigate targets that are up to several kilometers deep. Typically, acoustic pulses are generated at predetermined source locations s along the length of the reflection seismic profile. The information obtained from seismic reflection surveys can be used to define the geometry of the different. The seismic refraction method has not been used in the mining industry as widely as other geophysical methods. Although, active seismic methods have been very successfully used in exploration for oil and the theory and field procedures are well established, their use in. Chaubey national institute of oceanography, dona paula, goa403 004. In earlier days it was used in oil exploration but with the advent of seismic survey method in reflection its importance is lost. Seismic refraction and reflection methods geovision geophysicists conduct highresolution seismic refraction and seismic reflection surveys in support of a variety of engineering, environmental, and hydrogeologic investigations. The tx method averages out depth variations, although the plusminus method will show them from the same data it is incapable of fine detail, especially if the bedrock is irregular or lacks internal elastic contrasts. It plays a key role in the discovery of submarine gas hydrate. Sep 12, 2017 the seismic refraction method utilizes the refraction of seismic waves on geologic layers and rocksoil units in order to characterize the subsurface geologic conditions and geologic structure.
Difference between reflection and refraction compare the. Seismic refraction method the first seismic method utilized in the field of exploration. Latest posts by luzy r see all difference between stomach flu and food poisoning december 19, 2009. For free space, the onedimensional wave equation is derived. Seismic 2d reflection processing and interpretation of. The description of the geometry of refracted waves is more complex than that of reflected ones. Cost and frequency bandwidth are the principal differences between the two applications of seismic reflection. Thats of course in the context of exploration seismics. Comparing continuous profiles from masw and shearwave. P and swave seismic reflection and refraction measurements. Pdf reflection and refraction seismic on the great ancona landslide. Sep 26, 2012 its means that seismic waves by human divide by two techniques, refraction and reflection. Seismic refraction is a useful tool for the general investigation of bedrock structure, particularly at depth.
Seismic refraction measurements as described in this guide are applicable in mapping subsurface conditions for various uses including geologic, geotechnical, hydrologic, environmental, mineral exploration, petroleum exploration, and archaeological investigations. Jul 11, 2014 threedimensional seismic refraction tomography. Consequently, we provide here only a description of the fundamental aspects of the method. A comparison of reflection and refraction processing and. Seismic reflection refraction imaging has successfully been used in the oil industry to detect buried hydrocarbon traps for about 85 years dobrin, 1976. A nonmathematical discussion of seismic methods and the differences between reflection, refraction, and borehole seismology are given. Among other things, they are used to search for oil and gas deposits. Thus, the difference between deep petroleumoriented reflection and shallow reflection work suitable for engineering and environmental applications will be stressed. At such an interface, the energy within an incident seismic wave is partitioned into.
It was used in seismology for determining the mohorovicic discontinuity, and to discover the nuclei of earth. They follow the laws of reflection and refraction of optical waves in contact with two different media. Seismic reflection the return of some of the energy of seismic waves to earths surface after the waves bounce off a rock boundary seismic refraction the bending of seismic waves as they pass from one material to another. Seismic reflection methods applied to engineering, environmental. Reflection methods advantages disadvantages reflection seismic observations are collected at small sourcereceiver offsets. Another possibility of interpreting seismic refraction data is the refraction tomography, which is presented in chapter iv. The aim of this work was to use twodimensional reflection seismic processing methods to refraction seismic data collected from the onkalo area in year 2002, and to locate gently dipping reflectors from the stacked sections. Introduction to the interpretation of seismic refraction data. The wave phenomena occurring at a boundary between two layers are discussed, such as snells. Seismic refraction developed to locate artillery guns by measurement of recoil. The reader requiring greater detail is referred to the descriptions given by lankston 1990.
If external constraints are available, the velocitystructure profile can be transformed into a geologic model. For seismicexploration purposes, where measurements are taking place at the surface, the different arrivals of direct waves, reflected waves and refractedhead. Strategies for modelling seismic refraction wideangle reflection traveltimes to obtain 2d velocity and interface structure are presented along with methods for assessing the reliability of the. For both marine seismic reflection and refraction methods, the primary principles are based around the notion of sending artificiallygenerated sound waves downward into the earth and recording the energy that returns to recording instruments receivers. In reflection, the light returns to the same medium while in refraction, the light travels from one medium to another medium. Difference between reflection and refraction difference. Seismic refraction an overview sciencedirect topics. Reflection seismic methods can work no matter how the speed at which motions propagate through the earth varies with depth.
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