For seismicexploration purposes, where measurements are taking place at the surface, the different arrivals of direct waves, reflected waves and refractedhead. The seismic refraction method has not been used in the mining industry as widely as other geophysical methods. In the earth, seismic waves can propagate as longitudinal p or as shear s waves. Seismic resolution is controlled by the bandwidth of the signal, which is typically f30140 hz. 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.
They follow the laws of reflection and refraction of optical waves in contact with two different media. Seismic reflection and refraction are frequently practiced methods for mapping subsurface structure in sedimentary formation in connection with coal, oil, and gas exploration. 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. Ye yincan et al, in marine geohazards in china, 2017. Reflection methods advantages disadvantages reflection seismic observations are collected at small sourcereceiver offsets. In earlier days it was used in oil exploration but with the advent of seismic survey method in reflection its importance is lost. Common areas of dense seismic reflections were found between 75m and 300m across pure shear and converted wave images.
Before discussing any more differences between the refraction method and the reflection method, we. For free space, the onedimensional wave equation is derived. Seismic refraction survey in imperial valley geovision typically uses the oyo das1 or geometrics r2460 seismograph for refraction and reflection investigations. What is the difference between seismic reflection and refraction. Seismic refraction an overview sciencedirect topics. Seismic 2d reflection processing and interpretation of. 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. Penobscot bay, is here interpreted on the basis of both refracted and reflected phases. It plays a key role in the discovery of submarine gas hydrate. 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. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time. 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 was used in seismology for determining the mohorovicic discontinuity, and to discover the nuclei of earth.
Reflection seismic methods can work no matter how the speed at which motions propagate through the earth varies with depth. Latest posts by luzy r see all difference between stomach flu and food poisoning december 19, 2009. 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. The information obtained from seismic reflection surveys can be used to define the geometry of the different. Among other things, they are used to search for oil and gas deposits. 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. Difference between cell wall and cell membrane december 19, 2009. Seismic methods can provide valuable information of the subsurface, such as the seismic velocity structure of the geology e. Seismos company founded to use seismic refraction to map salt domes, often associated with hydrocarbon traps.
Jul 11, 2014 threedimensional seismic refraction tomography. Another possibility of interpreting seismic refraction data is the refraction tomography, which is presented in chapter iv. Here we present the results of seismic refraction and reflection studies. A comparison of reflection and refraction processing and. Cost and frequency bandwidth are the principal differences between the two applications of seismic reflection. Lecture 2 seismic refraction methods seismology refraction. Masw versus refraction seismic method in terms of acquisition and processing of data and the accuracy of estimation of velocity profiles. 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. 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. Masw versus refraction seismic method in terms of acquisition. One of the most important differences between the maps in figs.
When conducting seismic surveys, acoustic energy is input to the subsurface by an energy source such as a. Consequently, we provide here only a description of the fundamental aspects of the method. The description of the geometry of refracted waves is more complex than that of reflected ones. Furthermore is shown in chapter v, how the results of these two independent methods are used to get reliable information about the investigated area. What is the difference between reflection and refraction. Knowing the difference between reflection and refraction will help you understand basic phenomenon of science. Processing was done using mainly open source software seismic unix. Well log analysis exhibited possible sand zones at about 30m, 50m, 75m, and 122m. P and swave seismic reflection and refraction measurements. In principle, seismic data acquisition requires an energy source, a receiver, and a recording system. Thats of course in the context of exploration seismics. At such an interface, the energy within an incident seismic wave is partitioned into.
Seismic refraction method the first seismic method utilized in the field of exploration. Seismic reflection methods applied to engineering, environmental. Ppt seismic refraction powerpoint presentation free to. 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. 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. 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. Seismic reflection surveys have been used successfully in petroleum and geothermal exploration projects and to investigate for shallow coal. Seismic refraction provides engineers and geologists with the most basic of geologic data via simple procedures with common equipment. Pdf reflection and refraction seismic on the great ancona landslide. Seismic reflection and refraction are frequently practiced methods for mapping subsurface. Thus, the difference between deep petroleumoriented reflection and shallow reflection work suitable for engineering and environmental applications will be stressed. One of the founders of the seismic refraction method was german scientist ludger mintrop. Sep 26, 2012 its means that seismic waves by human divide by two techniques, refraction and reflection.
A comparison between masw and reflection methods based on the results of this study is summarized in table 2. Seismic refraction surveying universiti kebangsaan malaysia. Reflection and refraction seismic methods springerlink. The wave phenomena occurring at a boundary between two layers are discussed, such as snells. Refraction and reflection seismics serve different purposes. Introduction to seismic method linkedin slideshare. Chaubey national institute of oceanography, dona paula, goa403 004.
The reader requiring greater detail is referred to the descriptions given by lankston 1990. 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. The reflection seismic method is typically used to investigate targets that are up to several kilometers deep. 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 seismic reflection method involves the analysis of reflected waves, which occur later in the seismic record. The refraction seismic method is normally used for localized nearsurface investigations site surveys. Comparing continuous profiles from masw and shearwave. 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. Seismic refraction is a geophysical principle see refraction governed by snells law. On the flip side, refraction is when light is absorbed by the medium but the direction and speed is affected. A reflection gives out a perfect or almost perfect representation of an object. Basic principles of the seismic method tu delft opencourseware. 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.
Refraction, interpretation, seismic, reciprocal method, delay time, tomography introduction seismic refraction is considered to be paramount in engineering geophysics. Typically, acoustic pulses are generated at predetermined source locations s along the length of the reflection seismic profile. 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. 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. Measurement of seismicwave travel time is one of the most common geophysical method. 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.
Basic principles of the seismic method tu delft ocw. Seismic exploration is divided into refraction and reflection surveys, depending on whether the predominant portion of the seismic waves travel is ho. Introduction to the interpretation of seismic refraction data. 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. Seismic refraction developed to locate artillery guns by measurement of recoil. If external constraints are available, the velocitystructure profile can be transformed into a geologic model. Seismic reflection refraction imaging has successfully been used in the oil industry to detect buried hydrocarbon traps for about 85 years dobrin, 1976. Seismic refraction is a useful tool for the general investigation of bedrock structure, particularly at depth. 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. These methods include seismic reflection and refraction surveys, and travel time residual and attenuation studies. A comparative analysis of various seismic refraction.
Seismic methods are the most commonly conducted geophysical surveys for engineering investigations. Seismic energy is provided by a source shot located on the surface. 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. Reflection, is when the light goes back to the previous medium, but changes direction. Difference between reflection and refraction difference. Reflection frequencies decrease with depth because of attenuation of seismic waves, and this also decreases the resolution at depth. In reflection, the light returns to the same medium while in refraction, the light travels from one medium to another medium. Seismic reflection methods environmental geophysics us epa. Reflection and refraction seismology are both ways to study the structure of the earth near the surface. Refraction and reflection seismology physics stack exchange. Reflection seismic observations can be more readily interpreted in terms of complex geology. 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.
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